1
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Cardiff RL, Faulkner I, Beall J, Carothers JM, Zalatan J. CRISPR-Cas tools for simultaneous transcription & translation control in bacteria. Nucleic Acids Res 2024; 52:5406-5419. [PMID: 38613390 PMCID: PMC11109947 DOI: 10.1093/nar/gkae275] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/22/2023] [Revised: 03/27/2024] [Accepted: 04/05/2024] [Indexed: 04/14/2024] Open
Abstract
Robust control over gene translation at arbitrary mRNA targets is an outstanding challenge in microbial synthetic biology. The development of tools that can regulate translation will greatly expand our ability to precisely control genes across the genome. In Escherichia coli, most genes are contained in multi-gene operons, which are subject to polar effects where targeting one gene for repression leads to silencing of other genes in the same operon. These effects pose a challenge for independently regulating individual genes in multi-gene operons. Here, we use CRISPR-dCas13 to address this challenge. We find dCas13-mediated repression exhibits up to 6-fold lower polar effects compared to dCas9. We then show that we can selectively activate single genes in a synthetic multi-gene operon by coupling dCas9 transcriptional activation of an operon with dCas13 translational repression of individual genes within the operon. We also show that dCas13 and dCas9 can be multiplexed for improved biosynthesis of a medically-relevant human milk oligosaccharide. Taken together, our findings suggest that combining transcriptional and translational control can access effects that are difficult to achieve with either mode independently. These combined tools for gene regulation will expand our abilities to precisely engineer bacteria for biotechnology and perform systematic genetic screens.
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Affiliation(s)
- Ryan A L Cardiff
- Molecular Engineering & Sciences Institute and Center for Synthetic Biology University of Washington Seattle, WA 98195 USA
| | - Ian D Faulkner
- Department of Chemical Engineering University of Washington Seattle, WA 98195 USA
| | - Juliana G Beall
- Department of Chemistry University of Washington Seattle, WA 98195 USA
| | - James M Carothers
- Molecular Engineering & Sciences Institute and Center for Synthetic Biology University of Washington Seattle, WA 98195 USA
- Department of Chemical Engineering University of Washington Seattle, WA 98195 USA
| | - Jesse G Zalatan
- Molecular Engineering & Sciences Institute and Center for Synthetic Biology University of Washington Seattle, WA 98195 USA
- Department of Chemical Engineering University of Washington Seattle, WA 98195 USA
- Department of Chemistry University of Washington Seattle, WA 98195 USA
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2
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Sun G, DeFelice MM, Gillies TE, Ahn-Horst TA, Andrews CJ, Krummenacker M, Karp PD, Morrison JH, Covert MW. Cross-evaluation of E. coli's operon structures via a whole-cell model suggests alternative cellular benefits for low- versus high-expressing operons. Cell Syst 2024; 15:227-245.e7. [PMID: 38417437 PMCID: PMC10957310 DOI: 10.1016/j.cels.2024.02.002] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2023] [Revised: 09/12/2023] [Accepted: 02/08/2024] [Indexed: 03/01/2024]
Abstract
Many bacteria use operons to coregulate genes, but it remains unclear how operons benefit bacteria. We integrated E. coli's 788 polycistronic operons and 1,231 transcription units into an existing whole-cell model and found inconsistencies between the proposed operon structures and the RNA-seq read counts that the model was parameterized from. We resolved these inconsistencies through iterative, model-guided corrections to both datasets, including the correction of RNA-seq counts of short genes that were misreported as zero by existing alignment algorithms. The resulting model suggested two main modes by which operons benefit bacteria. For 86% of low-expression operons, adding operons increased the co-expression probabilities of their constituent proteins, whereas for 92% of high-expression operons, adding operons resulted in more stable expression ratios between the proteins. These simulations underscored the need for further experimental work on how operons reduce noise and synchronize both the expression timing and the quantity of constituent genes. A record of this paper's transparent peer review process is included in the supplemental information.
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Affiliation(s)
- Gwanggyu Sun
- Department of Bioengineering, Stanford University, Stanford, CA 94305, USA
| | - Mialy M DeFelice
- Department of Bioengineering, Stanford University, Stanford, CA 94305, USA
| | - Taryn E Gillies
- Department of Bioengineering, Stanford University, Stanford, CA 94305, USA
| | - Travis A Ahn-Horst
- Department of Bioengineering, Stanford University, Stanford, CA 94305, USA
| | - Cecelia J Andrews
- Department of Developmental Biology, Stanford University, Stanford, CA 94305, USA
| | | | | | - Jerry H Morrison
- Department of Bioengineering, Stanford University, Stanford, CA 94305, USA
| | - Markus W Covert
- Department of Bioengineering, Stanford University, Stanford, CA 94305, USA.
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3
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Fernández MB, Latorre L, Correa-Aragunde N, Cassia R. A putative bifunctional CPD/ (6-4) photolyase from the cyanobacteria Synechococcus sp. PCC 7335 is encoded by a UV-B inducible operon: New insights into the evolution of photolyases. Front Microbiol 2022; 13:981788. [DOI: 10.3389/fmicb.2022.981788] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2022] [Accepted: 09/26/2022] [Indexed: 11/13/2022] Open
Abstract
Photosynthetic organisms are continuously exposed to solar ultraviolet radiation-B (UV-B) because of their autotrophic lifestyle. UV-B provokes DNA damage, such as cyclobutane pyrimidine dimers (CPD) or pyrimidine (6-4) pyrimidone photoproducts (6-4 PPs). The cryptochrome/photolyase family (CPF) comprises flavoproteins that can bind damaged or undamaged DNA. Photolyases (PHRs) are enzymes that repair either CPDs or 6-4 PPs. A natural bifunctional CPD/(6-4)- PHR (PhrSph98) was recently isolated from the UV-resistant bacteria Sphingomonas sp. UV9. In this work, phylogenetic studies of bifunctional CPD/(6-4)- photolyases and their evolutionary relationship with other CPF members were performed. Amino acids involved in electron transfer and binding to FAD cofactor and DNA lesions were conserved in proteins from proteobacteria, planctomycete, bacteroidete, acidobacteria and cyanobacteria clades. Genome analysis revealed that the cyanobacteria Synechococcus sp. PCC 7335 encodes a two-gene assembly operon coding for a PHR and a bifunctional CPD/(6-4) PHR- like. Operon structure was validated by RT-qPCR analysis and the polycistronic transcript accumulated after 15 min of UV-B irradiation. Conservation of structure and evolution is discussed. This study provides evidence for a UV-B inducible PHR operon that encodes a CPD/(6-4)- photolyase homolog with a putative bifunctional role in the repair of CPDs and 6-4 PPs damages in oxygenic photosynthetic organisms.
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4
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Sun M, Gao AX, Li A, Liu X, Wang R, Yang Y, Li Y, Liu C, Bai Z. Bicistronic design as recombinant expression enhancer: characteristics, applications, and structural optimization. Appl Microbiol Biotechnol 2021; 105:7709-7720. [PMID: 34596722 DOI: 10.1007/s00253-021-11611-5] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2021] [Revised: 09/16/2021] [Accepted: 09/18/2021] [Indexed: 11/30/2022]
Abstract
The bicistronic design (BCD) is characterized by a short fore-cistron sequence and a second Shine-Dalgarno (SD2) sequence upstream of the target gene. The outstanding performance of this expression cassette in promoting recombinant protein production has attracted attention. Recently, the application of the BCD has been further extended to gene expression control, protein translation monitoring, and membrane protein production. In this review, we summarize the characteristics, molecular mechanisms, applications, and structural optimization of the BCD expression cassette. We also specifically discuss the challenges that the BCD system still faces. This is the first review of the BCD expression strategy, and it is believed that an in-depth understanding of the BCD will help researchers to better utilize and develop it. KEY POINTS: • Summary of the characteristics and molecular mechanisms of the BCD system. • Review of the actual applications of the BCD expression cassette. • Summary of the structural optimization of the BCD system.
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Affiliation(s)
- Manman Sun
- National Engineering Laboratory of Cereal Fermentation Technology, Jiangnan University, Wuxi, 214112, China.,Key Laboratory of Industrial Biotechnology, Ministry of Education, School of Biotechnology, Jiangnan University, Wuxi, 214122, China.,Jiangsu Provincial Research Center for Bioactive Product Processing Technology, Jiangnan University, Wuxi, 214122, China
| | - Alex Xiong Gao
- Division of Life Science, The Hong Kong University of Science and Technology, Hong Kong, China
| | - An Li
- National Engineering Laboratory of Cereal Fermentation Technology, Jiangnan University, Wuxi, 214112, China.,Key Laboratory of Industrial Biotechnology, Ministry of Education, School of Biotechnology, Jiangnan University, Wuxi, 214122, China.,Jiangsu Provincial Research Center for Bioactive Product Processing Technology, Jiangnan University, Wuxi, 214122, China
| | - Xiuxia Liu
- National Engineering Laboratory of Cereal Fermentation Technology, Jiangnan University, Wuxi, 214112, China. .,Key Laboratory of Industrial Biotechnology, Ministry of Education, School of Biotechnology, Jiangnan University, Wuxi, 214122, China. .,Jiangsu Provincial Research Center for Bioactive Product Processing Technology, Jiangnan University, Wuxi, 214122, China.
| | - Rongbing Wang
- National Engineering Laboratory of Cereal Fermentation Technology, Jiangnan University, Wuxi, 214112, China.,Key Laboratory of Industrial Biotechnology, Ministry of Education, School of Biotechnology, Jiangnan University, Wuxi, 214122, China.,Jiangsu Provincial Research Center for Bioactive Product Processing Technology, Jiangnan University, Wuxi, 214122, China
| | - Yankun Yang
- National Engineering Laboratory of Cereal Fermentation Technology, Jiangnan University, Wuxi, 214112, China.,Key Laboratory of Industrial Biotechnology, Ministry of Education, School of Biotechnology, Jiangnan University, Wuxi, 214122, China.,Jiangsu Provincial Research Center for Bioactive Product Processing Technology, Jiangnan University, Wuxi, 214122, China
| | - Ye Li
- National Engineering Laboratory of Cereal Fermentation Technology, Jiangnan University, Wuxi, 214112, China.,Key Laboratory of Industrial Biotechnology, Ministry of Education, School of Biotechnology, Jiangnan University, Wuxi, 214122, China.,Jiangsu Provincial Research Center for Bioactive Product Processing Technology, Jiangnan University, Wuxi, 214122, China
| | - Chunli Liu
- National Engineering Laboratory of Cereal Fermentation Technology, Jiangnan University, Wuxi, 214112, China.,Key Laboratory of Industrial Biotechnology, Ministry of Education, School of Biotechnology, Jiangnan University, Wuxi, 214122, China.,Jiangsu Provincial Research Center for Bioactive Product Processing Technology, Jiangnan University, Wuxi, 214122, China
| | - Zhonghu Bai
- National Engineering Laboratory of Cereal Fermentation Technology, Jiangnan University, Wuxi, 214112, China. .,Key Laboratory of Industrial Biotechnology, Ministry of Education, School of Biotechnology, Jiangnan University, Wuxi, 214122, China. .,Jiangsu Provincial Research Center for Bioactive Product Processing Technology, Jiangnan University, Wuxi, 214122, China.
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5
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Abstract
Bacterial protein synthesis rates have evolved to maintain preferred stoichiometries at striking precision, from the components of protein complexes to constituents of entire pathways. Setting relative protein production rates to be well within a factor of two requires concerted tuning of transcription, RNA turnover, and translation, allowing many potential regulatory strategies to achieve the preferred output. The last decade has seen a greatly expanded capacity for precise interrogation of each step of the central dogma genome-wide. Here, we summarize how these technologies have shaped the current understanding of diverse bacterial regulatory architectures underpinning stoichiometric protein synthesis. We focus on the emerging expanded view of bacterial operons, which encode diverse primary and secondary mRNA structures for tuning protein stoichiometry. Emphasis is placed on how quantitative tuning is achieved. We discuss the challenges and open questions in the application of quantitative, genome-wide methodologies to the problem of precise protein production. Expected final online publication date for the Annual Review of Microbiology, Volume 75 is October 2021. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.
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Affiliation(s)
- James C Taggart
- Department of Biology, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA; ,
| | - Jean-Benoît Lalanne
- Department of Biology, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA; , .,Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.,Current affiliation: Department of Genome Sciences, University of Washington, Seattle, Washington 98195, USA;
| | - Gene-Wei Li
- Department of Biology, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA; ,
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6
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Saito K, Green R, Buskirk AR. Ribosome recycling is not critical for translational coupling in Escherichia coli. eLife 2020; 9:59974. [PMID: 32965213 PMCID: PMC7538156 DOI: 10.7554/elife.59974] [Citation(s) in RCA: 18] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2020] [Accepted: 09/22/2020] [Indexed: 12/23/2022] Open
Abstract
We used ribosome profiling to characterize the biological role of ribosome recycling factor (RRF) in Escherichia coli. As expected, RRF depletion leads to enrichment of post-termination 70S complexes in 3′-UTRs. We also observe that elongating ribosomes are unable to complete translation because they are blocked by non-recycled ribosomes at stop codons. Previous studies have suggested a role for recycling in translational coupling within operons; if a ribosome remains bound to an mRNA after termination, it may re-initiate downstream. We found, however, that RRF depletion did not significantly affect coupling efficiency in reporter assays or in ribosome density genome-wide. These findings argue that re-initiation is not a major mechanism of translational coupling in E. coli. Finally, RRF depletion has dramatic effects on the activity of ribosome rescue factors tmRNA and ArfA. Our results provide a global view of the effects of the loss of ribosome recycling on protein synthesis in E. coli.
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Affiliation(s)
- Kazuki Saito
- Department of Molecular Biology and Genetics, Baltimore, United States
| | - Rachel Green
- Department of Molecular Biology and Genetics, Baltimore, United States.,Howard Hughes Medical Institute, Johns Hopkins University School of Medicine, Baltimore, United States
| | - Allen R Buskirk
- Department of Molecular Biology and Genetics, Baltimore, United States
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7
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Liang L, Haltli B, Marchbank DH, Fischer M, Kirby CW, Correa H, Clark TN, Gray CA, Kerr RG. Discovery of an Isothiazolinone-Containing Antitubercular Natural Product Levesquamide. J Org Chem 2020; 85:6450-6462. [PMID: 32363877 DOI: 10.1021/acs.joc.0c00339] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
Antitubercular agent levesquamide is a new polyketide-nonribosomal peptide (PK-NRP) hybrid marine natural product isolated from Streptomyces sp. RKND-216. The structure contains a rare isothiazolinone moiety which has only been reported in collismycin SN. Structure elucidation by NMR spectroscopy was a significant challenge due to a deficiency of protons in this aromatic moiety. Therefore, the genome of Streptomyces sp. RKND-216 was sequenced to identify the levesquamide biosynthetic gene cluster (BGC). Analysis of the BGC provided structural insights and guided stable-isotope labeling experiments, which led to the assignment of the fused pyridine-isothiazolinone moiety. The BGC and the labeling experiments provide further insights into the biosynthetic origin of isothiazolinones. Levesquamide exhibited antimicrobial activity in the microplate alamarBlue assay (MABA) and low oxygen recovery assay (LORA) against Mycobacterium tuberculosis H37Rv with minimum inhibitory concentration (MIC) values of 9.65 and 22.28 μM, respectively. Similar activity was exhibited against rifampicin- and isoniazid-resistant M. tuberculosis strains with MIC values of 9.46 and 9.90 μM, respectively. This result suggests levesquamide has a different mode of action against M. tuberculosis compared to the two first-line antitubercular drugs rifampicin and isoniazid. Furthermore, levesquamide shows no cytotoxicity against the Vero cell line, suggesting it may have a useful therapeutic window.
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Affiliation(s)
| | - Bradley Haltli
- Nautilus Biosciences Croda, 550 University Avenue, Regis and Joan Duffy Research Centre, Charlottetown, PE C1A 4P3, Canada
| | - Douglas H Marchbank
- Nautilus Biosciences Croda, 550 University Avenue, Regis and Joan Duffy Research Centre, Charlottetown, PE C1A 4P3, Canada
| | - Maike Fischer
- Charlottetown Research & Development Centre, Agriculture and Agri-Food Canada, 440 University Avenue, Charlottetown, PE C1A 4N6, Canada
| | - Christopher W Kirby
- Charlottetown Research & Development Centre, Agriculture and Agri-Food Canada, 440 University Avenue, Charlottetown, PE C1A 4N6, Canada
| | - Hebelin Correa
- Nautilus Biosciences Croda, 550 University Avenue, Regis and Joan Duffy Research Centre, Charlottetown, PE C1A 4P3, Canada
| | - Trevor N Clark
- Department of Chemistry, University of New Brunswick, 30 Dineen Drive, Fredericton, NB E3B 5A3, Canada
| | - Christopher A Gray
- Department of Chemistry, University of New Brunswick, 30 Dineen Drive, Fredericton, NB E3B 5A3, Canada.,Department of Biological Sciences, University of New Brunswick, 100 Tucker Park Road, Saint John, NB E2L 4L5, Canada
| | - Russell G Kerr
- Nautilus Biosciences Croda, 550 University Avenue, Regis and Joan Duffy Research Centre, Charlottetown, PE C1A 4P3, Canada
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8
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Monteagudo-Cascales E, García-Mauriño SM, Santero E, Canosa I. Unraveling the role of the CbrA histidine kinase in the signal transduction of the CbrAB two-component system in Pseudomonas putida. Sci Rep 2019; 9:9110. [PMID: 31235731 PMCID: PMC6591292 DOI: 10.1038/s41598-019-45554-9] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2019] [Accepted: 06/10/2019] [Indexed: 12/24/2022] Open
Abstract
The histidine kinase CbrA of the CbrAB two-component system of Pseudomonas putida is a key element to recognise the activating signal and mediate auto- and trans-phosphorylation of the response element CbrB. CbrA is encoded by the gene cbrA which is located downstream of a putative open reading frame we have named cbrX. We describe the role of the CbrX product in the expression of CbrA and show there is translational coupling of the genes. We also explore the role of the transmembrane (TM) and PAS domains of CbrA in the signal recognition. A ΔcbrXA mutant lacking its TM domains is uncoupled in its growth in histidine and citrate as carbon sources, but its overexpression restores the ability to grow in such carbon sources. In these conditions ΔTM-CbrA is able to respond to carbon availability, thus suggesting an intracellular nature for the signal sensed.
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Affiliation(s)
- Elizabet Monteagudo-Cascales
- Universidad Pablo de Olavide, Centro Andaluz de Biología del Desarrollo/Consejo Superior de Investigaciones Científicas/Junta de Andalucía, Seville, Spain
| | - Sofía M García-Mauriño
- Universidad Pablo de Olavide, Centro Andaluz de Biología del Desarrollo/Consejo Superior de Investigaciones Científicas/Junta de Andalucía, Seville, Spain
| | - Eduardo Santero
- Universidad Pablo de Olavide, Centro Andaluz de Biología del Desarrollo/Consejo Superior de Investigaciones Científicas/Junta de Andalucía, Seville, Spain
| | - Inés Canosa
- Universidad Pablo de Olavide, Centro Andaluz de Biología del Desarrollo/Consejo Superior de Investigaciones Científicas/Junta de Andalucía, Seville, Spain.
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9
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Duarte SOD, Martins MC, Andrade SM, Prazeres DMF, Monteiro GA. Plasmid Copy Number of pTRKH3 in Lactococcus lactis is Increased by Modification of the repDE Ribosome-Binding Site. Biotechnol J 2019; 14:e1800587. [PMID: 31009171 DOI: 10.1002/biot.201800587] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2018] [Revised: 04/02/2019] [Indexed: 01/08/2023]
Abstract
Plasmids for DNA vaccination are exclusively produced in the Gram-negative Escherichia coli. One important drawback of this system is the presence of lipopolysaccharides. The generally recognized as safe Lactococcus lactis (L. lactis) would constitute a safer alternative for plasmid production. A key requirement for the establishment of a cost-effective L. lactis-based plasmid manufacturing is the availability of high-copy number plasmids. Unfortunately, the highest copy number reported in Gram-positive bacteria for the pAMβ1 replicon is around 100 copies. The purpose of this work is to engineer the repDE ribosome-binding site (RBS) of the pTRKH3 plasmid by site-directed mutagenesis in order to increase the plasmid copy number in L. lactis LMG19460 cells. The pTRKH3-b mutant is the most promising candidate, achieving 215 copies of plasmid per chromosome, a 3.5-fold increase when compared to the nonmodified pTRKH3, probably due to a stronger RBS sequence, a messenger RNA secondary structure that promotes the RepDE expression, an ideal intermediate amount of transcriptional repressors and the presence of a duplicated region that added an additional RBS sequence and one new in-frame start codon. pTRKH3-b is a promising high-copy number shuttle plasmid that will contribute to turn lactic acid bacteria into a safer and economically viable alternative as DNA vaccines producers.
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Affiliation(s)
- Sofia O D Duarte
- iBB-Institute for Bioengineering and Biosciences, Instituto Superior Técnico, Universidade de Lisboa, 1049-001, Lisboa, Portugal
| | - Maria C Martins
- iBB-Institute for Bioengineering and Biosciences, Instituto Superior Técnico, Universidade de Lisboa, 1049-001, Lisboa, Portugal
| | - Sílvia M Andrade
- iBB-Institute for Bioengineering and Biosciences, Instituto Superior Técnico, Universidade de Lisboa, 1049-001, Lisboa, Portugal
| | - Duarte M F Prazeres
- iBB-Institute for Bioengineering and Biosciences, Instituto Superior Técnico, Universidade de Lisboa, 1049-001, Lisboa, Portugal.,Department of Bioengineering, Instituto Superior Técnico, Universidade de Lisboa, 1049-001, Lisboa, Portugal
| | - Gabriel A Monteiro
- iBB-Institute for Bioengineering and Biosciences, Instituto Superior Técnico, Universidade de Lisboa, 1049-001, Lisboa, Portugal.,Department of Bioengineering, Instituto Superior Técnico, Universidade de Lisboa, 1049-001, Lisboa, Portugal
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10
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Zhang F, Zhao Q, Tian J, Chang YF, Wen X, Huang X, Wu R, Wen Y, Yan Q, Huang Y, Ma X, Han X, Miao C, Cao S. Effective Pro-Inflammatory Induced Activity of GALT, a Conserved Antigen in A. Pleuropneumoniae, Improves the Cytokines Secretion of Macrophage via p38, ERK1/2 and JNK MAPKs Signal Pathway. Front Cell Infect Microbiol 2018; 8:337. [PMID: 30319993 PMCID: PMC6167544 DOI: 10.3389/fcimb.2018.00337] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2018] [Accepted: 09/03/2018] [Indexed: 12/17/2022] Open
Abstract
GALT is a highly conserved antigen in gram-negative bacteria, and has been shown to play a crucial role in the pathogenesis of many zoonoses. Actinobacillus pleuropneumoniae (APP) is a widespread respiratory system pathogen belonging to the Pasteuriaceae family. The functional mechanisms of GALT in the process of infection remain unclear. The aim of this study is to analyze roles of GALT in the pathogenesis of APP infection. Recombinant GALT was expressed in E. coli, purified, and was used to treat a Raw 264.7 macrophage line. Stimulation of Raw 264.7 macrophages with recombinant GALT protein induced the expression of pro-inflammatory cytokines (TNF-α, IL-1β, and IL-6). Compared with negative control, GALT led to increased production of pro-inflammatory cytokines in treated cells. Furthermore, specific inhibitors of the extracellular signal-regulated P38 and JNK MAPKs pathways significantly decreased GALT-induced pro-inflammatory cytokine production, and a western blot assay showed that GALT stimulation induced the activation of the MAPKs pathway. This process included cell-signaling pathways like P38, ERK1/2 and JNK MAPKs, and NF-κB. Both TLR2 and TLR4 were receptors of GALT antigens, whereas they played negative and positive roles (respectively) in the process of induction and expression of pro-inflammatory cytokines. Taken together, our data indicate that GALT is a novel pro-inflammatory mediator and induces TLR2 and TLR4-dependent pro-inflammatory activity in Raw 264.7 macrophages through P38, ERK1/2, and JNK MAPKs pathways.
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Affiliation(s)
- Fei Zhang
- College of Veterinary Medicine, Research Center of Swine Disease, Sichuan Agricultural University, Chengdu, China.,Department of Population Medicine and Diagnostic Sciences, College of Veterinary Medicine, Cornell University, Ithaca, NY, United States
| | - Qin Zhao
- College of Veterinary Medicine, Research Center of Swine Disease, Sichuan Agricultural University, Chengdu, China.,National Teaching and Experimental Center of Animal, Sichuan Agricultural University, Chengdu, China
| | - Jin Tian
- College of Veterinary Medicine, Research Center of Swine Disease, Sichuan Agricultural University, Chengdu, China
| | - Yung-Fu Chang
- Department of Population Medicine and Diagnostic Sciences, College of Veterinary Medicine, Cornell University, Ithaca, NY, United States
| | - Xintian Wen
- College of Veterinary Medicine, Research Center of Swine Disease, Sichuan Agricultural University, Chengdu, China.,Sichuan Science-Observation Experimental Station of Veterinary Drugs and Veterinary Diagnostic Technology, Ministry of Agriculture, Chengdu, China
| | - Xiaobo Huang
- College of Veterinary Medicine, Research Center of Swine Disease, Sichuan Agricultural University, Chengdu, China.,Sichuan Science-Observation Experimental Station of Veterinary Drugs and Veterinary Diagnostic Technology, Ministry of Agriculture, Chengdu, China
| | - Rui Wu
- College of Veterinary Medicine, Research Center of Swine Disease, Sichuan Agricultural University, Chengdu, China.,Sichuan Science-Observation Experimental Station of Veterinary Drugs and Veterinary Diagnostic Technology, Ministry of Agriculture, Chengdu, China
| | - Yiping Wen
- College of Veterinary Medicine, Research Center of Swine Disease, Sichuan Agricultural University, Chengdu, China.,Sichuan Science-Observation Experimental Station of Veterinary Drugs and Veterinary Diagnostic Technology, Ministry of Agriculture, Chengdu, China
| | - Qigui Yan
- College of Veterinary Medicine, Research Center of Swine Disease, Sichuan Agricultural University, Chengdu, China.,National Teaching and Experimental Center of Animal, Sichuan Agricultural University, Chengdu, China
| | - Yong Huang
- College of Veterinary Medicine, Research Center of Swine Disease, Sichuan Agricultural University, Chengdu, China.,National Teaching and Experimental Center of Animal, Sichuan Agricultural University, Chengdu, China
| | - Xiaoping Ma
- College of Veterinary Medicine, Research Center of Swine Disease, Sichuan Agricultural University, Chengdu, China.,National Teaching and Experimental Center of Animal, Sichuan Agricultural University, Chengdu, China
| | - Xinfeng Han
- College of Veterinary Medicine, Research Center of Swine Disease, Sichuan Agricultural University, Chengdu, China.,National Teaching and Experimental Center of Animal, Sichuan Agricultural University, Chengdu, China
| | - Chang Miao
- College of Veterinary Medicine, Research Center of Swine Disease, Sichuan Agricultural University, Chengdu, China
| | - Sanjie Cao
- College of Veterinary Medicine, Research Center of Swine Disease, Sichuan Agricultural University, Chengdu, China.,National Teaching and Experimental Center of Animal, Sichuan Agricultural University, Chengdu, China.,Sichuan Science-Observation Experimental Station of Veterinary Drugs and Veterinary Diagnostic Technology, Ministry of Agriculture, Chengdu, China
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11
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Mehrer CR, Incha MR, Politz MC, Pfleger BF. Anaerobic production of medium-chain fatty alcohols via a β-reduction pathway. Metab Eng 2018; 48:63-71. [PMID: 29807110 DOI: 10.1016/j.ymben.2018.05.011] [Citation(s) in RCA: 40] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2018] [Revised: 05/11/2018] [Accepted: 05/23/2018] [Indexed: 11/17/2022]
Abstract
In this report, we identify the relevant factors to increase production of medium chain n-alcohols through an expanded view of the reverse β-oxidation pathway. We began by creating a base strain capable of producing medium chain n-alcohols from glucose using a redox-balanced and growth-coupled metabolic engineering strategy. By dividing the heterologous enzymes in the pathway into different modules, we were able to identify and evaluate homologs of each enzyme within the pathway and identify several capable of enhancing medium chain alcohol titers and/or selectivity. In general, the identity of the trans-2-enoyl-CoA reductase (TER) and the direct overexpression of the thiolase (FadA) and β-hydroxy-acyl-CoA reductase (FadB) improved alcohol titer and the identity of the FadBA complex influenced the dominant chain length. Next, we linked the anaerobically induced VHb promoter from Vitreoscilla hemoglobin to each gene to remove the need for chemical inducers and ensure robust expression. The highest performing strain with the autoinduced reverse β-oxidation pathway produced n-alcohols at titers of 1.8 g/L with an apparent molar yield of 0.2 on glucose consumed in rich medium (52% of theoretical yield).
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Affiliation(s)
- Christopher R Mehrer
- Department of Chemical and Biological Engineering, University of Wisconsin-Madison, 3629 Engineering Hall, 1415 Engineering Drive, Madison, WI 53706, United States
| | - Matthew R Incha
- Department of Chemical and Biological Engineering, University of Wisconsin-Madison, 3629 Engineering Hall, 1415 Engineering Drive, Madison, WI 53706, United States
| | - Mark C Politz
- Department of Chemical and Biological Engineering, University of Wisconsin-Madison, 3629 Engineering Hall, 1415 Engineering Drive, Madison, WI 53706, United States
| | - Brian F Pfleger
- Department of Chemical and Biological Engineering, University of Wisconsin-Madison, 3629 Engineering Hall, 1415 Engineering Drive, Madison, WI 53706, United States; Microbiology Doctoral Training Program, University of Wisconsin-Madison, Madison, WI 53706, United States.
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12
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Buddeweg A, Sharma K, Urlaub H, Schmitz RA. sRNA 41 affects ribosome binding sites within polycistronic mRNAs in Methanosarcina mazei Gö1. Mol Microbiol 2018; 107:595-609. [PMID: 29271512 DOI: 10.1111/mmi.13900] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/13/2017] [Revised: 12/15/2017] [Accepted: 12/15/2017] [Indexed: 11/26/2022]
Abstract
Several noncoding RNAs potentially involved in nitrogen (N)-regulation have been detected in Methanosarcina mazei, however, targets have been identified only for one of them. Here, we report on the function of sRNA41 , highly expressed under N-sufficiency. Comprising 120 nucleotides, sRNA41 shows high sequence and structural conservation within draft genomes of numerous Methanosarcina species. In silico target prediction revealed several potential targets, including genes of two homologous operons encoding for acetyl-CoA-decarbonylase/synthase complexes (ACDS) representing highly probable target candidates. A highly conserved single stranded region of sRNA41 was predicted to mask six independent ribosome binding sites of these two polycistronic mRNAs and was verified in vitro by microscale thermophoresis. Proteome analysis of the respective sRNA41 -deletion mutant showed increased protein expression of both ACDS complexes in the absence of sRNA41 , whereas no effect on transcript levels was detected, arguing for sRNA41 -mediated post-transcriptional fine-tuning of ACDS expression. We hypothesize that the physiological advantage of downregulating sRNA41 under N-limiting conditions is the resulting increase of ACDS protein levels. This provides sufficient amounts of amino acids for nitrogenase synthesis as well as reducing equivalents and energy for N2 -fixation, thus linking the carbon and N-metabolism.
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Affiliation(s)
- Anne Buddeweg
- Christian-Albrechts-University Kiel, Institute for General Microbiology, Kiel, Germany
| | - Kundan Sharma
- Department of Clinical Chemistry, Bioanalytics Research Group, University Medical Centre, Göttingen, Germany.,Bioanalytical Mass Spectrometry Group, Max Planck Institute for Biophysical Chemistry, Göttingen, Germany
| | - Henning Urlaub
- Department of Clinical Chemistry, Bioanalytics Research Group, University Medical Centre, Göttingen, Germany.,Bioanalytical Mass Spectrometry Group, Max Planck Institute for Biophysical Chemistry, Göttingen, Germany
| | - Ruth A Schmitz
- Christian-Albrechts-University Kiel, Institute for General Microbiology, Kiel, Germany
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13
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Abstract
A general means of viral attenuation involves the extensive recoding of synonymous codons in the viral genome. The mechanistic underpinnings of this approach remain unclear, however. Using quantitative proteomics and RNA sequencing, we explore the molecular basis of attenuation in a strain of bacteriophage T7 whose major capsid gene was engineered to carry 182 suboptimal codons. We do not detect transcriptional effects from recoding. Proteomic observations reveal that translation is halved for the recoded major capsid gene, and a more modest reduction applies to several coexpressed downstream genes. We observe no changes in protein abundances of other coexpressed genes that are encoded upstream. Viral burst size, like capsid protein abundance, is also decreased by half. Together, these observations suggest that, in this virus, reduced translation of an essential polycistronic transcript and diminished virion assembly form the molecular basis of attenuation.
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14
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Liu X, Zhao Z, Zhang W, Sun Y, Yang Y, Bai Z. Bicistronic expression strategy for high-level expression of recombinant proteins in Corynebacterium glutamicum. Eng Life Sci 2017; 17:1118-1125. [PMID: 32624739 DOI: 10.1002/elsc.201700087] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2017] [Revised: 06/23/2017] [Accepted: 07/13/2017] [Indexed: 12/22/2022] Open
Abstract
Directly using the promoter associated with 5'-untranslated region of a high-protein-abundance gene from the genome may cause low expression activity of an expression system. A bicistronic expression part containing the short 5' coding sequence of the source gene and an embedded Shine-Dalgarno sequence can cause higher expression levels of the recombinant gene in a bicistronic cassette. Here, we evaluated two methods to construct expression parts and exploited genomic sequence sources to provide specific functional sequences to complete the expression system. The architecture of the bicistronic part increased the expression levels of target genes and performed more reliably than conventional expression parts with the same promoter and 5' untranslated region. For Corynebacterium glutamicum, the strongest bicistronic part, HP-BEP4, was obtained from a heterologous sequence source, leading to a 2.24-fold increase in the expression level of fluorescent protein over constitutively expressed pXMJ19 or the production of more than 100 mg/L single-chain variable fragment (scFv). It could meet the needs of overexpressing key genes in C. glutamicum.
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Affiliation(s)
- Xiuxia Liu
- National Engineering Laboratory for Cereal Fermentation Technology Jiangnan University Wuxi P. R. China.,The Key Laboratory of Industrial Biotechnology, Ministry of Education, School of Biotechnology Jiangnan University Wuxi P. R. China.,The Key Laboratory of Carbohydrate Chemistry and Biotechnology, Ministry of Education, School of Biotechnology Jiangnan University Wuxi P. R. China
| | - Zihao Zhao
- National Engineering Laboratory for Cereal Fermentation Technology Jiangnan University Wuxi P. R. China.,The Key Laboratory of Industrial Biotechnology, Ministry of Education, School of Biotechnology Jiangnan University Wuxi P. R. China.,The Key Laboratory of Carbohydrate Chemistry and Biotechnology, Ministry of Education, School of Biotechnology Jiangnan University Wuxi P. R. China
| | - Wei Zhang
- National Engineering Laboratory for Cereal Fermentation Technology Jiangnan University Wuxi P. R. China.,The Key Laboratory of Industrial Biotechnology, Ministry of Education, School of Biotechnology Jiangnan University Wuxi P. R. China.,The Key Laboratory of Carbohydrate Chemistry and Biotechnology, Ministry of Education, School of Biotechnology Jiangnan University Wuxi P. R. China
| | - Yang Sun
- National Engineering Laboratory for Cereal Fermentation Technology Jiangnan University Wuxi P. R. China.,The Key Laboratory of Industrial Biotechnology, Ministry of Education, School of Biotechnology Jiangnan University Wuxi P. R. China.,The Key Laboratory of Carbohydrate Chemistry and Biotechnology, Ministry of Education, School of Biotechnology Jiangnan University Wuxi P. R. China
| | - Yankun Yang
- National Engineering Laboratory for Cereal Fermentation Technology Jiangnan University Wuxi P. R. China.,The Key Laboratory of Industrial Biotechnology, Ministry of Education, School of Biotechnology Jiangnan University Wuxi P. R. China.,The Key Laboratory of Carbohydrate Chemistry and Biotechnology, Ministry of Education, School of Biotechnology Jiangnan University Wuxi P. R. China
| | - Zhonghu Bai
- National Engineering Laboratory for Cereal Fermentation Technology Jiangnan University Wuxi P. R. China.,The Key Laboratory of Industrial Biotechnology, Ministry of Education, School of Biotechnology Jiangnan University Wuxi P. R. China.,The Key Laboratory of Carbohydrate Chemistry and Biotechnology, Ministry of Education, School of Biotechnology Jiangnan University Wuxi P. R. China
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15
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Osamura T, Kawakami T, Kido R, Ishii M, Arai H. Specific expression and function of the A-type cytochrome c oxidase under starvation conditions in Pseudomonas aeruginosa. PLoS One 2017; 12:e0177957. [PMID: 28542449 PMCID: PMC5436846 DOI: 10.1371/journal.pone.0177957] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2016] [Accepted: 05/05/2017] [Indexed: 11/22/2022] Open
Abstract
Pseudomonas aeruginosa has one A-type (caa3) and multiple C-type (cbb3) cytochrome c oxidases as well as two quinol oxidases for aerobic respiration. The caa3 oxidase is highly efficient in creating a proton gradient across the cell membrane, but it is not expressed under normal growth conditions and its physiological role has not been investigated. In the present study, a mutant strain deficient in the coxBA-PA0107-coxC genes encoding caa3 exhibited normal growth under any test conditions, but it had low relative fitness under carbon starvation conditions, indicating that the expression of caa3 is advantageous under starvation conditions. A mutant that lacked four terminal oxidase gene clusters except for the cox genes was unable to grow aerobically because of low expression level of caa3. However, suppressor mutants that grew aerobically using caa3 as the only terminal oxidase emerged after aerobic subculturing. Analyses of the suppressor mutants revealed that a mutation of roxS encoding a sensor kinase of a two-component regulator RoxSR was necessary for the aerobic growth in synthetic medium. Two additional mutations in the 5′-flanking region of coxB were necessary for the aerobic growth in LB medium. Although the expression level of caa3 was higher in the suppressor mutants, their growth rates were lower than when the other terminal oxidases were utilized, suggesting that caa3 was not suited for utilization as the only terminal oxidase. Overexpression of the cox genes also inhibited the aerobic growth of the wild-type strain. These results indicate that caa3 is tightly regulated to be expressed only under starvation conditions at low level and it functions in cooperation with other terminal oxidases to facilitate survival in nutrient starvation conditions.
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Affiliation(s)
- Tatsuya Osamura
- Department of Biotechnology, The University of Tokyo, Bunkyo-ku, Tokyo, Japan
| | - Takuro Kawakami
- Department of Biotechnology, The University of Tokyo, Bunkyo-ku, Tokyo, Japan
| | - Reiko Kido
- Department of Biotechnology, The University of Tokyo, Bunkyo-ku, Tokyo, Japan
| | - Masaharu Ishii
- Department of Biotechnology, The University of Tokyo, Bunkyo-ku, Tokyo, Japan
| | - Hiroyuki Arai
- Department of Biotechnology, The University of Tokyo, Bunkyo-ku, Tokyo, Japan
- * E-mail:
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16
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Baggett NE, Zhang Y, Gross CA. Global analysis of translation termination in E. coli. PLoS Genet 2017; 13:e1006676. [PMID: 28301469 PMCID: PMC5373646 DOI: 10.1371/journal.pgen.1006676] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2016] [Revised: 03/30/2017] [Accepted: 03/08/2017] [Indexed: 01/01/2023] Open
Abstract
Terminating protein translation accurately and efficiently is critical for both protein fidelity and ribosome recycling for continued translation. The three bacterial release factors (RFs) play key roles: RF1 and 2 recognize stop codons and terminate translation; and RF3 promotes disassociation of bound release factors. Probing release factors mutations with reporter constructs containing programmed frameshifting sequences or premature stop codons had revealed a propensity for readthrough or frameshifting at these specific sites, but their effects on translation genome-wide have not been examined. We performed ribosome profiling on a set of isogenic strains with well-characterized release factor mutations to determine how they alter translation globally. Consistent with their known defects, strains with increasingly severe release factor defects exhibit increasingly severe accumulation of ribosomes over stop codons, indicative of an increased duration of the termination/release phase of translation. Release factor mutant strains also exhibit increased occupancy in the region following the stop codon at a significant number of genes. Our global analysis revealed that, as expected, translation termination is generally efficient and accurate, but that at a significant number of genes (≥ 50) the ribosome signature after the stop codon is suggestive of translation past the stop codon. Even native E. coli K-12 exhibits the ribosome signature suggestive of protein extension, especially at UGA codons, which rely exclusively on the reduced function RF2 variant of the K-12 strain for termination. Deletion of RF3 increases the severity of the defect. We unambiguously demonstrate readthrough and frameshifting protein extensions and their further accumulation in mutant strains for a few select cases. In addition to enhancing recoding, ribosome accumulation over stop codons disrupts attenuation control of biosynthetic operons, and may alter expression of some overlapping genes. Together, these functional alterations may either augment the protein repertoire or produce deleterious proteins. Proteins are the cellular workhorses, performing essentially all of the functions required for cell and organismal survival. But, it takes a great deal of energy to make proteins, making it critical that proteins are made accurately and in the proper time frame. After a ribosome synthesizes a protein, release factors catalyze the accurate and timely release of the finished protein from the ribosome, a process called termination. Ribosomes are then recycled and start the next protein. We utilized ribosome profiling, a method that allows us to follow the position of every ribosome that is making a protein, to globally investigate and strengthen insights on termination fidelity for cells with and without mutant release factors. We find that as we decrease release factor function, the time to terminate/release a protein increases across the genome. We observe that the accuracy of terminating a protein at the correct place decreases on a global scale. Using this metric we identify genes with inherently low termination efficiency and confirm two novel events resulting in extended protein products. In addition we find that beyond disrupting accurate protein synthesis, release factor mutations can alter expression of genes involved in the production of key amino acids.
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Affiliation(s)
- Natalie E. Baggett
- Department of Microbiology and Immunology, University of California, San Francisco, San Francisco, California, United States of America
| | - Yan Zhang
- Department of Microbiology and Immunology, University of California, San Francisco, San Francisco, California, United States of America
| | - Carol A. Gross
- Department of Microbiology and Immunology, University of California, San Francisco, San Francisco, California, United States of America
- Department of Cell and Tissue Biology, University of California, San Francisco, San Francisco, California, United States of America
- California Institute of Quantitative Biology, University of California, San Francisco, San Francisco, California, United States of America
- * E-mail:
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17
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Burkhardt DH, Rouskin S, Zhang Y, Li GW, Weissman JS, Gross CA. Operon mRNAs are organized into ORF-centric structures that predict translation efficiency. eLife 2017; 6. [PMID: 28139975 PMCID: PMC5318159 DOI: 10.7554/elife.22037] [Citation(s) in RCA: 99] [Impact Index Per Article: 14.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2016] [Accepted: 01/27/2017] [Indexed: 02/02/2023] Open
Abstract
Bacterial mRNAs are organized into operons consisting of discrete open reading frames (ORFs) in a single polycistronic mRNA. Individual ORFs on the mRNA are differentially translated, with rates varying as much as 100-fold. The signals controlling differential translation are poorly understood. Our genome-wide mRNA secondary structure analysis indicated that operonic mRNAs are comprised of ORF-wide units of secondary structure that vary across ORF boundaries such that adjacent ORFs on the same mRNA molecule are structurally distinct. ORF translation rate is strongly correlated with its mRNA structure in vivo, and correlation persists, albeit in a reduced form, with its structure when translation is inhibited and with that of in vitro refolded mRNA. These data suggest that intrinsic ORF mRNA structure encodes a rough blueprint for translation efficiency. This structure is then amplified by translation, in a self-reinforcing loop, to provide the structure that ultimately specifies the translation of each ORF. DOI:http://dx.doi.org/10.7554/eLife.22037.001 Proteins make up much of the biological machinery inside cells and perform the essential tasks needed to keep each cell alive. Cells contain thousands of different proteins and the instructions needed to build each protein are encoded in genes. However, these instructions cannot be used directly to manufacture the proteins. Instead, a messenger molecule called mRNA is needed to carry the information stored within genes to the parts of the cell where proteins are made. In bacteria, one mRNA molecule can include information from several genes. This group of genes is called an operon and produces a set of proteins that perform a shared task. Although these proteins work together, some of them are needed in greater numbers than others. Because they are all made using information from the same mRNA, some instructions on the mRNA must be read more times than others. It is unclear how bacterial cells control how many proteins are produced from each part of one mRNA but it is thought to relate to the three-dimensional shape of the molecule itself. Burkhardt, Rouskin, Zhang et al. have now examined the production of proteins from mRNAs in the commonly studied bacterium, Escherichia coli. The results showed that each set of instructions on the mRNA formed a three-dimensional structure that corresponds to the amount of protein produced from that portion of the mRNA. When this three-dimensional structure is more stable or rigid, the corresponding instructions tended to produce fewer proteins than if the structure was relatively simple and unstable. Further investigation showed that these three-dimensional mRNA structures could form spontaneously outside of cells, suggesting that molecules other than the mRNA itself have a relatively small role in controlling the number of proteins produced. This also suggests that the entire structure of each mRNA is important and is likely to be essential for cell survival. The next step is to understand why bacteria organise their genes in this way and how the different mRNA structures control how proteins are produced. Moreover, because many bacteria are used like biological factories to produce a variety of commercially useful molecules, these new insights have the potential to enhance a number of manufacturing processes. DOI:http://dx.doi.org/10.7554/eLife.22037.002
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Affiliation(s)
- David H Burkhardt
- Graduate Group in Biophysics, University of California, San Francisco, San Francisco, United States.,Department of Microbiology and Immunology, University of California, San Francisco, San Francisco, United States.,California Institute of Quantitative Biology, University of California, San Francisco, San Francisco, United States
| | - Silvi Rouskin
- California Institute of Quantitative Biology, University of California, San Francisco, San Francisco, United States.,Department of Cellular and Molecular Pharmacology, Howard Hughes Medical Institute, University of California, San Francisco, San Francisco, United States.,Center for RNA Systems Biology, University of California, San Francisco, San Francisco, United States
| | - Yan Zhang
- Department of Microbiology and Immunology, University of California, San Francisco, San Francisco, United States.,Department of Cell and Tissue Biology, University of California, San Francisco, San Francisco, United States
| | - Gene-Wei Li
- California Institute of Quantitative Biology, University of California, San Francisco, San Francisco, United States.,Department of Cellular and Molecular Pharmacology, Howard Hughes Medical Institute, University of California, San Francisco, San Francisco, United States.,Center for RNA Systems Biology, University of California, San Francisco, San Francisco, United States
| | - Jonathan S Weissman
- California Institute of Quantitative Biology, University of California, San Francisco, San Francisco, United States.,Department of Cellular and Molecular Pharmacology, Howard Hughes Medical Institute, University of California, San Francisco, San Francisco, United States.,Center for RNA Systems Biology, University of California, San Francisco, San Francisco, United States
| | - Carol A Gross
- Department of Microbiology and Immunology, University of California, San Francisco, San Francisco, United States.,California Institute of Quantitative Biology, University of California, San Francisco, San Francisco, United States.,Department of Cell and Tissue Biology, University of California, San Francisco, San Francisco, United States
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18
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19
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Sun WSW, Chen JW, Wu YC, Tsai HY, Kuo YL, Syu WJ. Expression Regulation of Polycistronic lee3 Genes of Enterohaemorrhagic Escherichia coli. PLoS One 2016; 11:e0155578. [PMID: 27182989 PMCID: PMC4868261 DOI: 10.1371/journal.pone.0155578] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2015] [Accepted: 05/01/2016] [Indexed: 01/21/2023] Open
Abstract
Enterohaemorrhagic Escherichia coli O157:H7 (EHEC) carries a pathogenic island LEE that is consisted mainly of five polycistronic operons. In the lee3 operon, mpc is the first gene and has been reported to down regulate the type-3 secretion system of EHEC when its gene product is over-expressed. Furthermore, mpc has been suggested to have a regulation function via translation but the mechanism remains unclear. To clarify this hypothesis, we dissected the polycistron and examined the translated products. We conclude that translation of mpc detrimentally governs the translation of the second gene, escV, which in turn affects the translation of the third gene, escN. Then sequentially, escN affects the expression of the downstream genes. Furthermore, we located a critical cis element within the mpc open-reading frame that plays a negative role in the translation-dependent regulation of lee3. Using qRT-PCR, we found that the amount of mpc RNA transcript present in EHEC was relatively limited when compared to any other genes within lee3. Taken together, when the transcription of LEE is activated, expression of mpc is tightly controlled by a restriction of the RNA transcript of mpc, translation of which is then critical for the efficient production of the operon’s downstream gene products.
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Affiliation(s)
- Wei-Sheng W. Sun
- Institute of Biochemistry and Molecular Biology, National Yang-Ming University, Taipei, Taiwan, R.O.C
- Taiwan International Graduate Program in Molecular Medicine, Academia Sinica, Taipei, Taiwan, R.O.C
| | - Jenn-Wei Chen
- Department of Microbiology and Immunology, National Cheng-Kung University, Tainan, Taiwan, R.O.C
| | - Yi-Chih Wu
- Institute of Microbiology and Immunology, National Yang-Ming University, Taipei, Taiwan, R.O.C
| | - Hsing-Yuan Tsai
- Institute of Microbiology and Immunology, National Yang-Ming University, Taipei, Taiwan, R.O.C
| | - Yu-Liang Kuo
- Department of Medical Imaging and Radiological Sciences, Chung Shan Medical University, Taichung, Taiwan, R.O.C
- Department of Medical Imaging, Chung Shan Medical University Hospital, Taichung, Taiwan, R.O.C
| | - Wan-Jr Syu
- Taiwan International Graduate Program in Molecular Medicine, Academia Sinica, Taipei, Taiwan, R.O.C
- Institute of Microbiology and Immunology, National Yang-Ming University, Taipei, Taiwan, R.O.C
- * E-mail:
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20
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Tian T, Salis HM. A predictive biophysical model of translational coupling to coordinate and control protein expression in bacterial operons. Nucleic Acids Res 2015; 43:7137-51. [PMID: 26117546 PMCID: PMC4538824 DOI: 10.1093/nar/gkv635] [Citation(s) in RCA: 71] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2015] [Accepted: 06/08/2015] [Indexed: 11/15/2022] Open
Abstract
Natural and engineered genetic systems require the coordinated expression of proteins. In bacteria, translational coupling provides a genetically encoded mechanism to control expression level ratios within multi-cistronic operons. We have developed a sequence-to-function biophysical model of translational coupling to predict expression level ratios in natural operons and to design synthetic operons with desired expression level ratios. To quantitatively measure ribosome re-initiation rates, we designed and characterized 22 bi-cistronic operon variants with systematically modified intergenic distances and upstream translation rates. We then derived a thermodynamic free energy model to calculate de novo initiation rates as a result of ribosome-assisted unfolding of intergenic RNA structures. The complete biophysical model has only five free parameters, but was able to accurately predict downstream translation rates for 120 synthetic bi-cistronic and tri-cistronic operons with rationally designed intergenic regions and systematically increased upstream translation rates. The biophysical model also accurately predicted the translation rates of the nine protein atp operon, compared to ribosome profiling measurements. Altogether, the biophysical model quantitatively predicts how translational coupling controls protein expression levels in synthetic and natural bacterial operons, providing a deeper understanding of an important post-transcriptional regulatory mechanism and offering the ability to rationally engineer operons with desired behaviors.
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Affiliation(s)
- Tian Tian
- Department of Biological Engineering, Pennsylvania State University, University Park, PA 16802, USA
| | - Howard M Salis
- Department of Biological Engineering, Pennsylvania State University, University Park, PA 16802, USA Department of Chemical Engineering, Pennsylvania State University, University Park, PA 16802, USA
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21
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Two-level inhibition of galK expression by Spot 42: Degradation of mRNA mK2 and enhanced transcription termination before the galK gene. Proc Natl Acad Sci U S A 2015; 112:7581-6. [PMID: 26045496 DOI: 10.1073/pnas.1424683112] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The Escherichia coli gal operon has the structure Pgal-galE-galT-galK-galM. During early log growth, a gradient in gene expression, named type 2 polarity, is established, as follows: galE > galT > galK > galM. However, during late-log growth, type 1 polarity is established in which galK is greater than galT, as follows: galE > galK > galT > galM. We found that type 2 polarity occurs as a result of the down-regulation of galK, which is caused by two different molecular mechanisms: Spot 42-mediated degradation of the galK-specific mRNA, mK2, and Spot 42-mediated Rho-dependent transcription termination at the end of galT. Because the concentration of Spot 42 drops during the transition period of the polarity type switch, these results demonstrate that type 1 polarity is the result of alleviation of Spot 42-mediated galK down-regulation. Because the Spot 42-binding site overlaps with a putative Rho-binding site, a molecular mechanism is proposed to explain how Spot 42, possibly with Hfq, enhances Rho-mediated transcription termination at the end of galT.
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22
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Tipton KA, Coleman JP, Pesci EC. Post-transcriptional regulation of gene PA5507 controls Pseudomonas quinolone signal concentration in P. aeruginosa. Mol Microbiol 2015; 96:670-83. [PMID: 25662317 DOI: 10.1111/mmi.12963] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 02/04/2015] [Indexed: 11/29/2022]
Abstract
Pseudomonas aeruginosa can sense and respond to a myriad of environmental signals and utilizes a system of small molecules to communicate through intercellular signaling. The small molecule 2-heptyl-3-hydroxy-4-quinolone (Pseudomonas Quinolone Signal [PQS]) is one of these signals and its synthesis is important for virulence. Previously, we identified an RpiR-type transcriptional regulator, QapR, that positively affects PQS production by repressing the qapR operon. An in-frame deletion of this regulator caused P. aeruginosa to produce a greatly reduced concentration of PQS. Here, we report that QapR translation is linked to the downstream gene PA5507. We found that introduction of a premature stop codon within qapR eliminates transcriptional autorepression of the qapR operon as expected but has no effect on PQS concentration. This was investigated with a series of lacZ reporter fusions which showed that translation of QapR must terminate at, or close to, the native qapR stop codon in order for translation of PA5507 to occur. Also, it was shown that truncation of the 5' end of the qapR transcript permitted PA5507 translation without translation of QapR. Our findings led us to conclude that PA5507 transcription and translation are both tightly controlled by QapR and this control is important for PQS homeostasis.
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Affiliation(s)
- Kyle A Tipton
- Department of Microbiology and Immunology, The Brody School of Medicine at East Carolina University, 600 Moye Blvd., Greenville, North Carolina, 27834, USA
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23
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Mukherjee S, Seok SC, Vieland VJ, Das J. Cell responses only partially shape cell-to-cell variations in protein abundances in Escherichia coli chemotaxis. Proc Natl Acad Sci U S A 2013; 110:18531-6. [PMID: 24167288 PMCID: PMC3832028 DOI: 10.1073/pnas.1311069110] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
Cell-to-cell variations in protein abundance in clonal cell populations are ubiquitous in living systems. Because protein composition determines responses in individual cells, it stands to reason that the variations themselves are subject to selective pressures. However, the functional role of these cell-to-cell differences is not well understood. One way to tackle questions regarding relationships between form and function is to perturb the form (e.g., change the protein abundances) and observe the resulting changes in some function. Here, we take on the form-function relationship from the inverse perspective, asking instead what specific constraints on cell-to-cell variations in protein abundance are imposed by a given functional phenotype. We develop a maximum entropy-based approach to posing questions of this type and illustrate the method by application to the well-characterized chemotactic response in Escherichia coli. We find that full determination of observed cell-to-cell variations in protein abundances is not inherent in chemotaxis itself but, in fact, appears to be jointly imposed by the chemotaxis program in conjunction with other factors (e.g., the protein synthesis machinery and/or additional nonchemotactic cell functions, such as cell metabolism). These results illustrate the power of maximum entropy as a tool for the investigation of relationships between biological form and function.
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Affiliation(s)
- Sayak Mukherjee
- Battelle Center for Mathematical Medicine, The Research Institute at the Nationwide Children’s Hospital, and
| | - Sang-Cheol Seok
- Battelle Center for Mathematical Medicine, The Research Institute at the Nationwide Children’s Hospital, and
| | - Veronica J. Vieland
- Battelle Center for Mathematical Medicine, The Research Institute at the Nationwide Children’s Hospital, and
- Departments of Pediatrics
- Statistics, and
| | - Jayajit Das
- Battelle Center for Mathematical Medicine, The Research Institute at the Nationwide Children’s Hospital, and
- Departments of Pediatrics
- Physics
- Biophysics Graduate Program, The Ohio State University, Columbus, OH 43205
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24
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Levin-Karp A, Barenholz U, Bareia T, Dayagi M, Zelcbuch L, Antonovsky N, Noor E, Milo R. Quantifying translational coupling in E. coli synthetic operons using RBS modulation and fluorescent reporters. ACS Synth Biol 2013; 2:327-36. [PMID: 23654261 DOI: 10.1021/sb400002n] [Citation(s) in RCA: 85] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Translational coupling is the interdependence of translation efficiency of neighboring genes encoded within an operon. The degree of coupling may be quantified by measuring how the translation rate of a gene is modulated by the translation rate of its upstream gene. Translational coupling was observed in prokaryotic operons several decades ago, but the quantitative range of modulation translational coupling leads to and the factors governing this modulation were only partially characterized. In this study, we systematically quantify and characterize translational coupling in E. coli synthetic operons using a library of plasmids carrying fluorescent reporter genes that are controlled by a set of different ribosome binding site (RBS) sequences. The downstream gene expression level is found to be enhanced by the upstream gene expression via translational coupling with the enhancement level varying from almost no coupling to over 10-fold depending on the upstream gene's sequence. Additionally, we find that the level of translational coupling in our system is similar between the second and third locations in the operon. The coupling depends on the distance between the stop codon of the upstream gene and the start codon of the downstream gene. This study is the first to systematically and quantitatively characterize translational coupling in a synthetic E. coli operon. Our analysis will be useful in accurate manipulation of gene expression in synthetic biology and serves as a step toward understanding the mechanisms involved in translational expression modulation.
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Affiliation(s)
- Ayelet Levin-Karp
- Department of Plant Sciences, Weizmann Institute of Science, Rehovot 76100, Israel
| | - Uri Barenholz
- Department of Plant Sciences, Weizmann Institute of Science, Rehovot 76100, Israel
| | - Tasneem Bareia
- Department of Plant Sciences, Weizmann Institute of Science, Rehovot 76100, Israel
| | - Michal Dayagi
- Department of Plant Sciences, Weizmann Institute of Science, Rehovot 76100, Israel
| | - Lior Zelcbuch
- Department of Plant Sciences, Weizmann Institute of Science, Rehovot 76100, Israel
| | - Niv Antonovsky
- Department of Plant Sciences, Weizmann Institute of Science, Rehovot 76100, Israel
| | - Elad Noor
- Department of Plant Sciences, Weizmann Institute of Science, Rehovot 76100, Israel
| | - Ron Milo
- Department of Plant Sciences, Weizmann Institute of Science, Rehovot 76100, Israel
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Precise and reliable gene expression via standard transcription and translation initiation elements. Nat Methods 2013; 10:354-60. [DOI: 10.1038/nmeth.2404] [Citation(s) in RCA: 541] [Impact Index Per Article: 49.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2012] [Accepted: 02/14/2013] [Indexed: 01/19/2023]
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Zelcbuch L, Antonovsky N, Bar-Even A, Levin-Karp A, Barenholz U, Dayagi M, Liebermeister W, Flamholz A, Noor E, Amram S, Brandis A, Bareia T, Yofe I, Jubran H, Milo R. Spanning high-dimensional expression space using ribosome-binding site combinatorics. Nucleic Acids Res 2013; 41:e98. [PMID: 23470993 PMCID: PMC3643573 DOI: 10.1093/nar/gkt151] [Citation(s) in RCA: 132] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022] Open
Abstract
Protein levels are a dominant factor shaping natural and synthetic biological systems. Although proper functioning of metabolic pathways relies on precise control of enzyme levels, the experimental ability to balance the levels of many genes in parallel is a major outstanding challenge. Here, we introduce a rapid and modular method to span the expression space of several proteins in parallel. By combinatorially pairing genes with a compact set of ribosome-binding sites, we modulate protein abundance by several orders of magnitude. We demonstrate our strategy by using a synthetic operon containing fluorescent proteins to span a 3D color space. Using the same approach, we modulate a recombinant carotenoid biosynthesis pathway in Escherichia coli to reveal a diversity of phenotypes, each characterized by a distinct carotenoid accumulation profile. In a single combinatorial assembly, we achieve a yield of the industrially valuable compound astaxanthin 4-fold higher than previously reported. The methodology presented here provides an efficient tool for exploring a high-dimensional expression space to locate desirable phenotypes.
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Affiliation(s)
- Lior Zelcbuch
- Department of Plant Sciences, Weizmann Institute of Science, Rehovot 76100, Israel
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27
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New insights into small RNA-dependent translational regulation in prokaryotes. Trends Genet 2013; 29:92-8. [DOI: 10.1016/j.tig.2012.10.004] [Citation(s) in RCA: 83] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2012] [Revised: 09/14/2012] [Accepted: 10/04/2012] [Indexed: 12/16/2022]
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A translation-coupling DNA cassette for monitoring protein translation in Escherichia coli. Metab Eng 2012; 14:298-305. [PMID: 22575266 DOI: 10.1016/j.ymben.2012.04.005] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2012] [Revised: 04/22/2012] [Accepted: 04/24/2012] [Indexed: 11/24/2022]
Abstract
A major challenge to using heterologous expression in metabolic engineering experiments is the inability to quickly dissect experiments that have failed at the stage of translating mRNA. While many methods of detecting proteins exist, methods that detect untagged proteins at low levels are limited. Here, we describe a method to quickly determine whether Escherichia coli is capable of expressing the product of any target gene by coupling translation of a target gene to a detectable response gene. A translational coupling cassette was designed to encode a mRNA sequence that forms a secondary structure in the absence of translation and contains the translational start sequence of a detectable response gene. The translational coupling method was successfully tested with fluorescent proteins and antibiotic resistance markers. Only when the target gene was fully translated was the response observed. Further characterization demonstrated that translational coupling functions at both low and high levels of expression and that the response signal is proportional to the amount of target gene product. The translational coupling system was used to determine that a large multi-domain enzyme was not actively translated in E. coli, to isolate the translation problems to the C-terminal domains, and to optimize conditions for expressing a codon-optimized sequence variant.
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Siibak T, Peil L, Dönhöfer A, Tats A, Remm M, Wilson DN, Tenson T, Remme J. Antibiotic-induced ribosomal assembly defects result from changes in the synthesis of ribosomal proteins. Mol Microbiol 2011; 80:54-67. [PMID: 21320180 DOI: 10.1111/j.1365-2958.2011.07555.x] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
Inhibitors of protein synthesis cause defects in the assembly of ribosomal subunits. In response to treatment with the antibiotics erythromycin or chloramphenicol, precursors of both large and small ribosomal subunits accumulate. We have used a pulse-labelling approach to demonstrate that the accumulating subribosomal particles maturate into functional 70S ribosomes. The protein content of the precursor particles is heterogeneous and does not correspond with known assembly intermediates. Mass spectrometry indicates that production of ribosomal proteins in the presence of the antibiotics correlates with the amounts of the individual ribosomal proteins within the precursor particles. Thus, treatment of cells with chloramphenicol or erythromycin leads to an unbalanced synthesis of ribosomal proteins, providing the explanation for formation of assembly-defective particles. The operons for ribosomal proteins show a characteristic pattern of antibiotic inhibition where synthesis of the first proteins is inhibited weakly but gradually increases for the subsequent proteins in the operon. This phenomenon most likely reflects translational coupling and allows us to identify other putative coupled non-ribosomal operons in the Escherichia coli chromosome.
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Affiliation(s)
- Triinu Siibak
- Institutes of Molecular and Cell Biology Technology, University of Tartu, Tartu, Estonia
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Identification and characterization of a heme periplasmic-binding protein in Haemophilus ducreyi. Biometals 2011; 24:709-22. [PMID: 21347851 DOI: 10.1007/s10534-011-9427-4] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/24/2010] [Accepted: 02/03/2011] [Indexed: 10/18/2022]
Abstract
Haemophilus ducreyi, a gram-negative and heme-dependent bacterium, is the causative agent of chancroid, a genital ulcer sexually transmitted infection. Heme acquisition in H. ducreyi proceeds via a receptor mediated process in which the initial event involves binding of hemoglobin and heme to their cognate outer membrane proteins, HgbA and TdhA, respectively. Following this specific interaction, the fate of the periplasmic deposited heme is unclear. Using protein expression profiling of the H. ducreyi periplasmic proteome, a periplasmic-binding protein, termed hHbp, was identified whose expression was enhanced under heme-limited conditions. The gene encoding this protein was situated in a locus displaying genetic characteristics of an ABC transporter. The purified protein bound heme in a dose-dependent and saturable manner and this binding was specifically competitively inhibited by heme. The hhbp gene functionally complemented an Escherichia coli heme uptake mutant. Expression of the heme periplasmic-binding protein was detected in a limited survey of H. ducreyi and H. influenzae clinical strains. These results indicate that the passage of heme into the cytoplasm of H. ducreyi involves a heme dedicated ABC transporter.
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31
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Kaw MK, Blumenthal RM. Translational independence between overlapping genes for a restriction endonuclease and its transcriptional regulator. BMC Mol Biol 2010; 11:87. [PMID: 21092102 PMCID: PMC2997769 DOI: 10.1186/1471-2199-11-87] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2010] [Accepted: 11/19/2010] [Indexed: 01/09/2023] Open
Abstract
Background Most type II restriction-modification (RM) systems have two independent enzymes that act on the same DNA sequence: a modification methyltransferase that protects target sites, and a restriction endonuclease that cleaves unmethylated target sites. When RM genes enter a new cell, methylation must occur before restriction activity appears, or the host's chromosome is digested. Transcriptional mechanisms that delay endonuclease expression have been identified in some RM systems. A substantial subset of those systems is controlled by a family of small transcription activators called C proteins. In the PvuII system, C.PvuII activates transcription of its own gene, along with that of the downstream endonuclease gene. This regulation results in very low R.PvuII mRNA levels early after gene entry, followed by rapid increase due to positive feedback. However, given the lethal consequences of premature REase accumulation, transcriptional control alone might be insufficient. In C-controlled RM systems, there is a ± 20 nt overlap between the C termination codon and the R (endonuclease) initiation codon, suggesting possible translational coupling, and in many cases predicted RNA hairpins could occlude the ribosome binding site for the endonuclease gene. Results Expression levels of lacZ translational fusions to pvuIIR or pvuIIC were determined, with the native pvuII promoter having been replaced by one not controlled by C.PvuII. In-frame pvuIIC insertions did not substantially decrease either pvuIIC-lacZ or pvuIIR-lacZ expression (with or without C.PvuII provided in trans). In contrast, a frameshift mutation in pvuIIC decreased expression markedly in both fusions, but mRNA measurements indicated that this decrease could be explained by transcriptional polarity. Expression of pvuIIR-lacZ was unaffected when the pvuIIC stop codon was moved 21 nt downstream from its WT location, or 25 or 40 bp upstream of the pvuIIR initiation codon. Disrupting the putative hairpins had no significant effects. Conclusions The initiation of translation of pvuIIR appears to be independent of that for pvuIIC. Direct tests failed to detect regulatory rules for either gene overlap or the putative hairpins. Thus, at least during balanced growth, transcriptional control appears to be sufficiently robust for proper regulation of this RM system.
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Affiliation(s)
- Meenakshi K Kaw
- Department of Medical Microbiology and Immunology, University of Toledo Health Science Campus, 3100 Transverse Drive, Toledo, OH 43614-2598, USA
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Gatenby AA, Rothstein SJ, Nomura M. Translational coupling of the maize chloroplast atpB and atpE genes. Proc Natl Acad Sci U S A 2010; 86:4066-70. [PMID: 16594048 PMCID: PMC287389 DOI: 10.1073/pnas.86.11.4066] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The genes for the beta and epsilon subunits of maize chloroplast ATP synthase are encoded by the organelle genome, are cotranscribed, and have overlapping translation initiation and termination codons. To determine whether the atpB and atpE genes are translationally coupled, they were transformed into Escherichia coli on a multicopy plasmid. Synthesis of full-length beta and epsilon polypeptides demonstrated correct initiation of translation by the bacterial ribosomes. To assay for translational coupling, the promoter-distal atpE gene was fused to lacZ, resulting in the synthesis of an active hybrid beta-galactosidase. A frameshift mutation was introduced into the promoter-proximal atpB gene, and its effect on the transcription and translation of the atpE::lacZ fusion was measured. The mutation resulted in a 1000- to 2000-fold reduction in beta-galactosidase activity, but only a 2-fold decrease in LacZ mRNA synthesis rates or galactoside transacetylase levels. Similar results were obtained when the atpB/atpE::lacZ fusion and the atpB frameshift mutation were introduced into the photosynthetic cyanobacterium Synechocystis sp. PCC6803. We show that >99% of atpE translation depends on successful translation of atpB and, thus, conclude that the two genes are translationally coupled.
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Affiliation(s)
- A A Gatenby
- Institute for Enzyme Research, University of Wisconsin, Madison, WI 53706
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Løvdok L, Bentele K, Vladimirov N, Müller A, Pop FS, Lebiedz D, Kollmann M, Sourjik V. Role of translational coupling in robustness of bacterial chemotaxis pathway. PLoS Biol 2009; 7:e1000171. [PMID: 19688030 PMCID: PMC2716512 DOI: 10.1371/journal.pbio.1000171] [Citation(s) in RCA: 52] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2008] [Accepted: 07/07/2009] [Indexed: 11/30/2022] Open
Abstract
Evolutionary selection for robustness of signaling output in the face of stochastic variations in protein expression may explain the organization of bacterial chemotaxis genes. Chemotaxis allows bacteria to colonize their environment more efficiently and to find optimal growth conditions, and is consequently under strong evolutionary selection. Theoretical and experimental analyses of bacterial chemotaxis suggested that the pathway has been evolutionarily optimized to produce robust output under conditions of such physiological perturbations as stochastic intercellular variations in protein levels while at the same time minimizing complexity and cost of protein expression. Pathway topology in Escherichia coli apparently evolved to produce an invariant output under concerted variations in protein levels, consistent with experimentally observed transcriptional coupling of chemotaxis genes. Here, we show that the pathway robustness is further enhanced through the pairwise translational coupling of adjacent genes. Computer simulations predicted that the robustness of the pathway against the uncorrelated variations in protein levels can be enhanced by a selective pairwise coupling of individual chemotaxis genes on one mRNA, with the order of genes in E. coli ranking among the best in terms of noise compensation. Translational coupling between chemotaxis genes was experimentally confirmed, and coupled expression of these genes was shown to improve chemotaxis. Bioinformatics analysis further revealed that E. coli gene order corresponds to consensus in sequenced bacterial genomes, confirming evolutionary selection for noise reduction. Since polycistronic gene organization is common in bacteria, translational coupling between adjacent genes may provide a general mechanism to enhance robustness of their signaling and metabolic networks. Moreover, coupling between expression of neighboring genes is also present in eukaryotes, and similar principles of noise reduction might thus apply to all cellular networks. All cellular networks are subject to fluctuations in the levels of their components. Robustness of the network output in the face of stochastic gene expression, or gene expression noise, is therefore essential to ensure proper function. Selection for robustness might thus have shaped much of the cellular evolution. We have used Escherichia coli chemotaxis, one of the most thoroughly studied model systems for signal transduction, to analyze the role of gene organization in robustness. Our mathematical modeling predicted that coupling the expression of chemotaxis proteins with opposing functions should buffer the output of the signaling pathway against stochastic variations in protein production. Consistent with this model, protein coexpression was indeed observed to improve chemotaxis and to be under selection during chemotaxis-driven spreading of a cell population. We show that tight coexpression is ensured by both transcriptional and translational gene coupling. We conclude that evolutionary selection for pathway robustness in the presence of gene expression noise can explain, not only the polycistronic organization of chemotaxis genes, but also the gene order within chemotaxis operons. Selection on the gene order was further confirmed by the observation of a strong bias towards specific pairwise occurrences of chemotaxis genes in sequenced prokaryotic genomes.
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Affiliation(s)
- Linda Løvdok
- Zentrum für Molekulare Biologie der Universität Heidelberg, DKFZ-ZMBH Alliance, Heidelberg, Germany
| | - Kajetan Bentele
- Institut für Theoretische Biologie, Humboldt Universität, Berlin, Germany
| | - Nikita Vladimirov
- Interdisziplinäres Zentrum für Wissenschaftliches Rechnen der Universität Heidelberg, Heidelberg, Germany
| | - Anette Müller
- Zentrum für Molekulare Biologie der Universität Heidelberg, DKFZ-ZMBH Alliance, Heidelberg, Germany
| | - Ferencz S. Pop
- Zentrum für Molekulare Biologie der Universität Heidelberg, DKFZ-ZMBH Alliance, Heidelberg, Germany
| | - Dirk Lebiedz
- Zentrum für Biosystemanalyze, Universität Freiburg, Freiburg, Germany
| | - Markus Kollmann
- Institut für Theoretische Biologie, Humboldt Universität, Berlin, Germany
- * E-mail: (MK); (VS)
| | - Victor Sourjik
- Zentrum für Molekulare Biologie der Universität Heidelberg, DKFZ-ZMBH Alliance, Heidelberg, Germany
- * E-mail: (MK); (VS)
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Gulevich AY, Skorokhodova AY, Ermishev VY, Krylov AA, Minaeva NI, Polonskaya ZM, Zimenkov DV, Biryukova IV, Mashko SV. A new method for the construction of translationally coupled operons in a bacterial chromosome. Mol Biol 2009; 43:505-11. [DOI: 10.1134/s0026893309030194] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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35
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Jacquier H, Zaoui C, Sanson-le Pors MJ, Mazel D, Berçot B. Translation regulation of integrons gene cassette expression by the attC sites. Mol Microbiol 2009; 72:1475-86. [PMID: 19486293 DOI: 10.1111/j.1365-2958.2009.06736.x] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
Integron are genetic elements able to carry, capture and shuffle the genes embedded in gene cassettes. The attC recombination sites adopt a stable secondary structure when single-stranded that is necessary for their recombination. In this study, we evaluated the impact of the structure of the attC site on expression of the 3' gene in class 1 integrons. This was analysed by substituting the attC of the bla(IMP-8) gene cassette with various mutated attC sites spanning a wide range of sizes and secondary structures, and measuring the integron-dependent translation of the 3'aac(6')-Ib7 gene. In the resulting constructs, the 5'-attC site differentially affected the expression of the aac(6')-Ib7 gene. Contrary to what was expected from their proposed role as Rho-independent transcription terminators, the transcription of the aac(6')-Ib7 gene was not affected by the various attC sites. Mutations of natural sites revealed that destabilization of the potential stem-loop structure of the attC site in the transcript could enhance the expression of the 3' gene. In particular, the presence of a translated open reading frame was shown to increase translation of the 3' gene. These findings might be explained by the capacity of the stem-loop structures to impede ribosome progression.
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Affiliation(s)
- Hervé Jacquier
- Assistance Publique Hôpitaux de Paris, Hôpital Lariboisière, Service de Bactériologie-Virologie, Université Paris VII, 2 rue Ambroise Paré, 75010 Paris, France
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A novel bicistronic vector for overexpressing Mycobacterium tuberculosis proteins in Escherichia coli. Protein Expr Purif 2008; 65:230-7. [PMID: 19162193 DOI: 10.1016/j.pep.2008.12.013] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2008] [Revised: 12/19/2008] [Accepted: 12/20/2008] [Indexed: 01/24/2023]
Abstract
A putative DNA glycosylase encoded by the Rv3297 gene (MtuNei2) has been identified in Mycobacterium tuberculosis. Our efforts to express this gene in Escherichia coli either by supplementing tRNAs for rare codons or optimizing the gene with preferred codons for E. coli resulted in little or no expression. On the other hand, high-level expression was observed using a bicistronic expression vector in which the target gene was translationally coupled to an upstream leader sequence. Further comparison of the predicted mRNA secondary structures supported the hypothesis that mRNA secondary structure(s) surrounding the translation initiation region (TIR), rather than codon usage, played the dominant role in influencing translation efficiency, although manipulation of codon usage or tRNA supplementation did further enhance expression in the bicistronic vector. Addition of a cleavable N-terminal tag also facilitated gene expression in E. coli, possibly through a similar mechanism. However, since cleavage of N-terminal tags is determined by the amino acid at the P(1)' position downstream of the protease recognition sequence and results in the addition of an extra amino acid in front of the N-terminus of the protein, this strategy is not particularly amenable to Fpg/Nei family DNA glycosylases which carry the catalytic proline residue at the P(1)' position and require a free N-terminus. On the other hand, the bicistronic vector constructed here is potentially valuable particularly when expressing proteins from G/C rich organisms and when the proteins carry proline residues at the N-terminus in their native form. Thus the bicistronic expression system can be used to improve translation efficiency of mRNAs and achieve high-level expression of mycobacterial genes in E. coli.
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Lee SJ, Ko JH, Kang HY, Lee Y. Coupled expression of MhpE aldolase and MhpF dehydrogenase in Escherichia coli. Biochem Biophys Res Commun 2006; 346:1009-15. [PMID: 16782065 DOI: 10.1016/j.bbrc.2006.06.009] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/22/2006] [Accepted: 06/02/2006] [Indexed: 11/17/2022]
Abstract
MhpE (4-hydroxy-2-ketovalerate aldolase) and MhpF [acetaldehyde dehydrogenase (acylating)] are responsible for the last two reactions in the 3-(3-hydroxyphenyl)propionate (3-HPP) catabolic pathway in Escherichia coli, which is homologous to the meta-cleavage pathway in Pseudomonas species. Here, we report that the MhpE aldolase is associated with the MhpF dehydrogenase and that MhpF is indispensable for the folding of MhpE. Moreover, our results suggest that the mhpF and mhpE genes are translationally coupled through a reinitiation mechanism. This reinitiation mechanism may function in ensuring that the expression of mhpE occurs only when MhpF is available for the formation of a complex.
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Affiliation(s)
- Sang-Joon Lee
- Department of Chemistry and Center for Molecular Design and Synthesis, Korea Advanced Institute of Science and Technology, Daejeon 305-701, Republic of Korea
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Zhang Z, Dietrich FS. Identification and characterization of upstream open reading frames (uORF) in the 5' untranslated regions (UTR) of genes in Saccharomyces cerevisiae. Curr Genet 2005; 48:77-87. [PMID: 16012843 DOI: 10.1007/s00294-005-0001-x] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2005] [Revised: 05/23/2005] [Accepted: 05/30/2005] [Indexed: 01/17/2023]
Abstract
We have taken advantage of recently sequenced hemiascomycete fungal genomes to computationally identify additional genes potentially regulated by upstream open reading frames (uORFs). Our approach is based on the observation that the structure, including the uORFs, of the post-transcriptionally uORF regulated Saccharomyces cerevisiae genes GCN4 and CPA1 is conserved in related species. Thirty-eight candidate genes for which uORFs were found in multiple species were identified and tested. We determined by 5' RACE that 15 of these 38 genes are transcribed. Most of these 15 genes have only a single uORF in their 5' UTR, and the length of these uORFs range from 3 to 24 codons. We cloned seven full-length UTR sequences into a luciferase (LUC) reporter system. Luciferase activity and mRNA level were compared between the wild-type UTR construct and a construct where the uORF start codon was mutated. The translational efficiency index (TEI) of each construct was calculated to test the possible regulatory function on translational level. We hypothesize that uORFs in the UTR of RPC11, TPK1, FOL1, WSC3, and MKK1 may have translational regulatory roles while uORFs in the 5' UTR of ECM7 and IMD4 have little effect on translation under the conditions tested.
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Affiliation(s)
- Zhihong Zhang
- Department of Molecular Genetics and Microbiology, Duke University Medical Center, Durham, NC 27710, USA
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Karamyshev AL, Karamysheva ZN, Yamami T, Ito K, Nakamura Y. Transient idling of posttermination ribosomes ready to reinitiate protein synthesis. Biochimie 2005; 86:933-8. [PMID: 15667944 DOI: 10.1016/j.biochi.2004.08.006] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2004] [Accepted: 08/12/2004] [Indexed: 11/25/2022]
Abstract
The fate of ribosomes between termination and initiation during protein synthesis is very basic, yet poorly understood. Here we found that translational reinitiation of the alkaline phosphatase gene occurs in Escherichia coli from an internal methionine codon when the authentic translation is prematurely terminated at a nonsense codon that is within seven codons upstream of the reinitiation codon (which we refer to as "reinitiation window"). Changing the reading frame downstream of the stop codon did not abolish the reinitiation, while inactivating the upstream initiation codon abolished the reinitiation. Moreover, depletion of the ribosome recycling factor (RRF), which disassembles posttermination ribosomes in conjunction with elongation factor G, did not influence the observed reinitiation. These findings suggest that posttermination ribosomes can undergo a transient idling state ready to reinitiate protein synthesis even in the absence of the Shine-Dalgarno (SD) sequence within the reinitiation window by evading disengagement from the mRNA.
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Affiliation(s)
- Andrey L Karamyshev
- Department of Basic Medical Sciences, Institute of Medical Science, University of Tokyo, 4-6-1 Shirokanedai, Minato-ku, Tokyo 108-8639, Japan
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Coombs JT, Franco CMM, Loria R. Complete sequencing and analysis of pEN2701, a novel 13-kb plasmid from an endophytic Streptomyces sp. Plasmid 2003; 49:86-92. [PMID: 12584005 DOI: 10.1016/s0147-619x(02)00153-1] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
A 12,855 bp cryptic plasmid was isolated from strains of an endophytic Streptomyces sp. over a wide geographical area in South Australia. This plasmid was completely sequenced and 13 putative ORFs were identified. Two of the ORFs may be involved in the regulation of host plant genes. ORF7 exhibited homology to a plant transcriptional regulatory protein and ORF1 was a homolog of a plant protein synthesis initiation factor. The plasmid appears to use a novel transfer mechanism for a Streptomyces plasmid. Pocks were detected during conjugative transfer and kor but not tra homologs could be identified. This structure and the sequence of the putative Kor protein are similar to the pFQ series of plasmids isolated from Frankia, another endophytic actinomycete.
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Affiliation(s)
- Justin T Coombs
- Plant Pathology Department, Cornell University, Ithaca, NY 14850, USA.
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Kelsall A, Evans C, Busby S. A plasmid vector that allows fusion of theEscherichia coligalactokinase gene to the translation startpoint of other genes. FEBS Lett 2001. [DOI: 10.1016/0014-5793(85)81062-0] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
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Yu JS, Madison-Antenucci S, Steege DA. Translation at higher than an optimal level interferes with coupling at an intercistronic junction. Mol Microbiol 2001; 42:821-34. [PMID: 11722745 DOI: 10.1046/j.1365-2958.2001.02681.x] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
In pairs of adjacent genes co-transcribed on bacterial polycistronic mRNAs, translation of the first coding region frequently functions as a positive factor to couple translation to the distal coding region. Coupling efficiencies vary over a wide range, but synthesis of both gene products at similar levels is common. We report the results of characterizing an unusual gene pair, in which only about 1% of the translational activity from the upstream gene is transmitted to the distal gene. The inefficient coupling was unexpected because the upstream gene is highly translated, the distal initiation site has weak but intrinsic ability to bind ribosomes, and the AUG is only two nucleotides beyond the stop codon for the upstream gene. The genes are those in the filamentous phage IKe genome, which encode the abundant single-stranded DNA binding protein (gene V) and the minor coat protein that caps one tip of the phage (gene VII). Here, we have used chimeras between the related phage IKe and f1 sequences to localize the region responsible for inefficient coupling. It mapped upstream from the intercistronic region containing the gene V stop codon and the gene VII initiation site, indicating that low coupling efficiency is associated with gene V. The basis for inefficient coupling emerged when coupling efficiency was found to increase as gene V translation was decreased below the high wild-type level. This was achieved by lowering the rate of elongation and by decreasing the efficiency of suppression at an amber codon within the gene. Increasing the strength of the Shine-Dalgarno interaction with 16S rRNA at the gene VII start also increased coupling efficiency substantially. In this gene pair, upstream translation thus functions in an unprecedented way as a negative factor to limit downstream expression. We interpret the results as evidence that translation in excess of an optimal level in an upstream gene interferes with coupling in the intercistronic junction.
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Affiliation(s)
- J S Yu
- Department of Biochemistry, Duke University Medical Center, Durham, NC 27710, USA
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Fridjonsson O, Mattes R. Production of recombinant alpha-galactosidases in Thermus thermophilus. Appl Environ Microbiol 2001; 67:4192-8. [PMID: 11526023 PMCID: PMC93147 DOI: 10.1128/aem.67.9.4192-4198.2001] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/05/2001] [Accepted: 06/26/2001] [Indexed: 11/20/2022] Open
Abstract
A Thermus thermophilus selector strain for production of thermostable and thermoactive alpha-galactosidase was constructed. For this purpose, the native alpha-galactosidase gene (agaT) of T. thermophilus TH125 was inactivated to prevent background activity. In our first attempt, insertional mutagenesis of agaT by using a cassette carrying a kanamycin resistance gene led to bacterial inability to utilize melibiose (alpha-galactoside) and galactose as sole carbohydrate sources due to a polar effect of the insertional inactivation. A Gal(+) phenotype was assumed to be essential for growth on melibiose. In a Gal(-) background, accumulation of galactose or its metabolite derivatives produced from melibiose hydrolysis could interfere with the growth of the host strain harboring recombinant alpha-galactosidase. Moreover, the AgaT(-) strain had to be Km(s) for establishment of the plasmids containing alpha-galactosidase genes and the kanamycin resistance marker. Therefore, a suitable selector strain (AgaT(-) Gal(+) Km(s)) was generated by applying integration mutagenesis in combination with phenotypic selection. To produce heterologous alpha-galactosidase in T. thermophilus, the isogenes agaA and agaB of Bacillus stearothermophilus KVE36 were cloned into an Escherichia coli-Thermus shuttle vector. The region containing the E. coli plasmid sequence (pUC-derived vector) was deleted before transformation of T. thermophilus with the recombinant plasmids. As a result, transformation efficiency and plasmid stability were improved. However, growth on minimal agar medium containing melibiose was achieved only following random selection of the clones carrying a plasmid-based mutation that had promoted a higher copy number and greater stability of the plasmid.
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Affiliation(s)
- E Fuchs
- Institute of Molecular Genetics, University of Heidelberg, Germany
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Abstract
When the same sequence of nucleotides codes for regions of more than one functional polypeptide, this sequence contains overlapping genes. Overlap is most common in rapidly evolving genomes with high mutation rates such as viruses, bacteria, and mitochondria. Overlap is thought to be important as: (1) a means of compressing a maximum amount of information into short sequences of structural genes; and (2) as a mechanism for regulating gene expression through translational coupling of functionally related polypeptides. The stability of overlapping codes is examined in relation to the information cost of overlap and the mutation rate of the genome. The degree of overlap in a given population will tend to become monomorphic. Evolution toward partial overlap of genes is shown to depend on a convex cost function of overlap. Overlap does not evolve when expression of overlapping genes is mutually exclusive and produced by rare mutations to the wild-type genome. Assuming overlap increases coupling between functionally related genes, the conditions favoring overlap are explored in relation to the kinetics of gene activation and decay. Coupling is most effective for genes in which the gene overlapping at its 5' end (leading gene) decays rapidly, while the gene overlapping at the 3' end (induced gene) decays slowly. If gene expression can feedback on itself (autocatalysis), then high rates of activation favor overlap.
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Affiliation(s)
- D C Krakauer
- Institute for Advanced Study, Princeton, New Jersey 08540, USA.
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Fukuda Y, Washio T, Tomita M. Comparative study of overlapping genes in the genomes of Mycoplasma genitalium and Mycoplasma pneumoniae. Nucleic Acids Res 1999; 27:1847-53. [PMID: 10101192 PMCID: PMC148392 DOI: 10.1093/nar/27.8.1847] [Citation(s) in RCA: 47] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Overlapping genes are defined, in this paper, as a pair of adjacent genes whose coding regions are partly overlapping. We systematically analyzed all overlapping genes in the genomes of two closely related species: Mycoplasma genitalium and Mycoplasma pneumoniae. Careful comparisons were made for homologous genes that are overlapped in one species but not in the other. This comparative analysis allows us to propose a model of how overlapping genes emerged in the course of evolution. It was found that overlapping genes were generated primarily due to the loss of a stop codon in either gene, in many cases, the absence of which resulted in elongation of the 3' end of the gene's coding region. More specifically, the loss of the stop codon took place as a result of the following events: deletion of the stop codon (64.4%), point mutation at the stop codon (4.4%), and frame shift at the end of the coding region (6.7%). Overlapping genes, in a sense, can be thought of as the results of evolutionary pressure to minimize genome size. However, our analysis indicates that many overlapping genes, at least in the genomes of M.genitalium and M.pneumoniae, are due to incidental elongation of the coding regions.
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Affiliation(s)
- Y Fukuda
- Laboratory for Bioinformatics, Department of Environmental Information and Graduate School of Media and Governance, Keio University, 5322 Endo, Fujisawa 252, Japan
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Abstract
Studies of the budding yeast Saccharomyces cerevisiae have greatly advanced our understanding of the posttranscriptional steps of eukaryotic gene expression. Given the wide range of experimental tools applicable to S. cerevisiae and the recent determination of its complete genomic sequence, many of the key challenges of the posttranscriptional control field can be tackled particularly effectively by using this organism. This article reviews the current knowledge of the cellular components and mechanisms related to translation and mRNA decay, with the emphasis on the molecular basis for rate control and gene regulation. Recent progress in characterizing translation factors and their protein-protein and RNA-protein interactions has been rapid. Against the background of a growing body of structural information, the review discusses the thermodynamic and kinetic principles that govern the translation process. As in prokaryotic systems, translational initiation is a key point of control. Modulation of the activities of translational initiation factors imposes global regulation in the cell, while structural features of particular 5' untranslated regions, such as upstream open reading frames and effector binding sites, allow for gene-specific regulation. Recent data have revealed many new details of the molecular mechanisms involved while providing insight into the functional overlaps and molecular networking that are apparently a key feature of evolving cellular systems. An overall picture of the mechanisms governing mRNA decay has only very recently begun to develop. The latest work has revealed new information about the mRNA decay pathways, the components of the mRNA degradation machinery, and the way in which these might relate to the translation apparatus. Overall, major challenges still to be addressed include the task of relating principles of posttranscriptional control to cellular compartmentalization and polysome structure and the role of molecular channelling in these highly complex expression systems.
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Affiliation(s)
- J E McCarthy
- Posttranscriptional Control Group, Department of Biomolecular Sciences, University of Manchester Institute of Science and Technology (UMIST), Manchester M60 1QD, United Kingdom.
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Liu X, DeMoss JA. Characterization of NarJ, a system-specific chaperone required for nitrate reductase biogenesis in Escherichia coli. J Biol Chem 1997; 272:24266-71. [PMID: 9305880 DOI: 10.1074/jbc.272.39.24266] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
The narGHJI operon encodes the three subunits, alpha, beta, and gamma, of the respiratory nitrate reductase complex in Escherichia coli. A fourth open reading frame of the operon encodes a putative protein, NarJ, which is not present in purified nitrate reductase, but is required for biogenesis of the membrane-bound complex. NarJ was identified with a T7 expression system and was produced at significantly less than stoichiometric levels relative to the three enzyme subunits. A functional His-tagged NarJ fusion protein was overexpressed from a multicopy plasmid, purified by Ni2+ affinity chromatography, and characterized. Western blot analysis with antibodies raised against the fusion protein demonstrated that NarJ remained in the cytosol after assembly of the active membrane complex. The cytosolic alphabeta complex accumulated in a narJ insertion mutant was rapidly degraded after induction, but was stabilized by NarJ expressed from a multicopy plasmid. Overproduction of the His-tagged NarJ fusion protein in the same mutant led to the formation of an alphabeta.NarJ complex, which was resolved by Ni2+ affinity chromatography. The NarJ protein therefore has the properties of a system-specific (private) chaperone that reacts directly with and modifies the properties of the cytosolic alphabeta subunit complex, but remains in the cytoplasm after the assembly of the active alphabetagamma complex in the membrane.
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Affiliation(s)
- X Liu
- Department of Biochemistry and Molecular Biology, University of Texas Houston Medical School, Houston, Texas 77030, USA
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Penfold CN, Bender CL, Turner JG. Characterisation of genes involved in biosynthesis of coronafacic acid, the polyketide component of the phytotoxin coronatine. Gene X 1996; 183:167-73. [PMID: 8996103 DOI: 10.1016/s0378-1119(96)00550-1] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
Coronafacic acid (CFA) is the polyketide component of coronatine (COR), a phytotoxin produced by the plant pathogen, Pseudomonas syringae. In the present study we have determined the nucleotide sequence of a 3.92-kb DNA fragment involved in CFA biosynthesis. Analysis of the sequence revealed four complete open reading frames (ORFs) designated cfa1 to cfa4 and one incomplete ORF (cfa5), all transcribed in the same direction. The predicted translation products of cfa1, cfa2 and cfa3 showed relatedness to acyl carrier proteins, fatty acid dehydrases and beta-ketoacylsynthases, respectively, which are required for polyketide synthesis. cfa1 was subcloned, its sequence was confirmed, and it was overexpressed in E. coli to yield a peptide with an apparent molecular mass of 6 kDa.
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Affiliation(s)
- C N Penfold
- Molecular Biology Sector, School of Biological Sciences, University of East Anglia, Norwich, UK
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