1
|
T N, Govindarajan S, Munavar MH. trans-translation system is important for maintaining genome integrity during DNA damage in bacteria. Res Microbiol 2023; 174:104136. [PMID: 37690591 DOI: 10.1016/j.resmic.2023.104136] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2023] [Revised: 08/29/2023] [Accepted: 08/31/2023] [Indexed: 09/12/2023]
Abstract
DNA integrity in bacteria is regulated by various factors that act on the DNA. trans-translation has previously been shown to be important for the survival of Escherichia coli cells exposed to certain DNA-damaging agents. However, the mechanisms underlying this sensitivity are poorly understood. In this study, we explored the involvement of the trans-translation system in the maintenance of genome integrity using various DNA-damaging agents and mutant backgrounds. Relative viability assays showed that SsrA-defective cells were sensitive to DNA-damaging agents, such as nalidixic acid (NA), ultraviolet radiation (UV), and methyl methanesulfonate (MMS). The viability of SsrA-defective cells was rescued by deleting sulA, although the expression of SulA was not more pronounced in SsrA-defective cells than in wild-type cells. Live cell imaging using a Gam-GFP fluorescent reporter showed increased double-strand breaks (DSBs) in SsrA-defective cells during DNA damage. We also showed that the ribosome rescue function of SsrA was sufficient for DNA damage tolerance. DNA damage sensitivity can be alleviated by partial uncoupling of transcription and translation by using sub-lethal concentrations of ribosome inhibiting antibiotic (tetracycline) or by mutating the gene coding for RNase H (rnhA). Taken together, our results highlight the importance of trans-translation system in maintaining genome integrity and bacterial survival during DNA damage.
Collapse
Affiliation(s)
- Nagarajan T
- Department of Molecular Biology, School of Biological Sciences, Madurai Kamaraj University, Madurai, India; Department of Biological Sciences, SRM University-AP, Amaravati, India
| | | | - M Hussain Munavar
- Department of Molecular Biology, School of Biological Sciences, Madurai Kamaraj University, Madurai, India.
| |
Collapse
|
2
|
Abstract
Despite having a highly reduced genome, Chlamydia trachomatis undergoes a complex developmental cycle in which the bacteria differentiate between the following two functionally and morphologically distinct forms: the infectious, nonreplicative elementary body (EB) and the noninfectious, replicative reticulate body (RB). The transitions between EBs and RBs are not mediated by division events that redistribute intracellular proteins. Rather, both primary (EB to RB) and secondary (RB to EB) differentiation likely require bulk protein turnover. One system for targeted protein degradation is the trans-translation system for ribosomal rescue, where polypeptides stalled during translation are marked with an SsrA tag encoded by a hybrid tRNA-mRNA, tmRNA. ClpX recognizes the SsrA tag, leading to ClpXP-mediated degradation. We hypothesize that ClpX functions in chlamydial differentiation through targeted protein degradation. We found that mutation of a key residue (R230A) within the specific motif in ClpX associated with the recognition of SsrA-tagged substrates resulted in abrogated secondary differentiation while not reducing chlamydial replication or developmental cycle progression as measured by transcripts. Furthermore, inhibition of trans-translation through chemical and targeted genetic approaches also impeded chlamydial development. Knockdown of tmRNA and subsequent complementation with an allele mutated in the SsrA tag closely phenocopied the overexpression of ClpXR230A, thus suggesting that ClpX recognition of SsrA-tagged substrates plays a critical function in secondary differentiation. Taken together, these data provide mechanistic insight into the requirements for transitions between chlamydial developmental forms. IMPORTANCE Chlamydia trachomatis is the leading cause of bacterial sexually transmitted infections and preventable infectious blindness. This unique organism undergoes developmental transitions between infectious, nondividing forms and noninfectious, dividing forms. Therefore, the chlamydial developmental cycle is an attractive target for Chlamydia-specific antibiotics, which would minimize effects of broad-spectrum antibiotics on the spread of antibiotic resistance in other organisms. However, the lack of knowledge about chlamydial development on a molecular level impedes the identification of specific, druggable targets. This work describes a mechanism through which both the fundamental processes of trans-translation and proteomic turnover by ClpXP contribute to chlamydial differentiation, a critical facet of chlamydial growth and survival. Given the almost universal presence of trans-translation and ClpX in eubacteria, this mechanism may be conserved in developmental cycles of other bacterial species. Additionally, this study expands the fields of trans-translation and Clp proteases by emphasizing the functional diversity of these systems throughout bacterial evolution.
Collapse
|
3
|
Computational modeling of unphosphorylated CtrA: Cori binding in the Caulobacter cell cycle. iScience 2021; 24:103413. [PMID: 34901785 PMCID: PMC8640480 DOI: 10.1016/j.isci.2021.103413] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2021] [Revised: 09/17/2021] [Accepted: 11/05/2021] [Indexed: 02/04/2023] Open
Abstract
In the alphaproteobacterium, Caulobacter crescentus, phosphorylated CtrA (CtrA∼P), a master regulatory protein, binds directly to the chromosome origin (Cori) to inhibit DNA replication. Using a mathematical model of CtrA binding at Cori site [d], we provide computational evidence that CtrAU can displace CtrA∼P from Cori at the G1-S transition. Investigation of this interaction within a detailed model of the C. crescentus cell cycle suggests that CckA phosphatase may clear Cori of CtrA∼P by altering the [CtrAU]/[CtrA∼P] ratio rather than by completely depleting CtrA∼P. Model analysis reveals that the mechanism allows for a speedier transition into S phase, stabilizes the timing of chromosome replication under fluctuating rates of CtrA proteolysis, and may contribute to the viability of numerous mutant strains. Overall, these results suggest that CtrAU enhances the robustness of chromosome replication. More generally, our proposed regulation of CtrA:Cori dynamics may represent a novel motif for molecular signaling in cell physiology.
Collapse
|
4
|
Felletti M, Romilly C, Wagner EGH, Jonas K. A nascent polypeptide sequence modulates DnaA translation elongation in response to nutrient availability. eLife 2021; 10:71611. [PMID: 34524083 PMCID: PMC8443254 DOI: 10.7554/elife.71611] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2021] [Accepted: 08/15/2021] [Indexed: 01/01/2023] Open
Abstract
The ability to regulate DNA replication initiation in response to changing nutrient conditions is an important feature of most cell types. In bacteria, DNA replication is triggered by the initiator protein DnaA, which has long been suggested to respond to nutritional changes; nevertheless, the underlying mechanisms remain poorly understood. Here, we report a novel mechanism that adjusts DnaA synthesis in response to nutrient availability in Caulobacter crescentus. By performing a detailed biochemical and genetic analysis of the dnaA mRNA, we identified a sequence downstream of the dnaA start codon that inhibits DnaA translation elongation upon carbon exhaustion. Our data show that the corresponding peptide sequence, but not the mRNA secondary structure or the codon choice, is critical for this response, suggesting that specific amino acids in the growing DnaA nascent chain tune translational efficiency. Our study provides new insights into DnaA regulation and highlights the importance of translation elongation as a regulatory target. We propose that translation regulation by nascent chain sequences, like the one described, might constitute a general strategy for modulating the synthesis rate of specific proteins under changing conditions.
Collapse
Affiliation(s)
- Michele Felletti
- Science for Life Laboratory and Department of Molecular Biosciences, The Wenner-Gren Institute, Stockholm University, Stockholm, Sweden
| | - Cédric Romilly
- Department of Cell and Molecular Biology, Uppsala University, Uppsala, Sweden
| | - E Gerhart H Wagner
- Department of Cell and Molecular Biology, Uppsala University, Uppsala, Sweden
| | - Kristina Jonas
- Science for Life Laboratory and Department of Molecular Biosciences, The Wenner-Gren Institute, Stockholm University, Stockholm, Sweden
| |
Collapse
|
5
|
Menikpurage IP, Woo K, Mera PE. Transcriptional Activity of the Bacterial Replication Initiator DnaA. Front Microbiol 2021; 12:662317. [PMID: 34140937 PMCID: PMC8203912 DOI: 10.3389/fmicb.2021.662317] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2021] [Accepted: 04/19/2021] [Indexed: 11/13/2022] Open
Abstract
In bacteria, DnaA is the most conserved DNA replication initiator protein. DnaA is a DNA binding protein that is part of the AAA+ ATPase family. In addition to initiating chromosome replication, DnaA can also function as a transcription factor either as an activator or repressor. The first gene identified to be regulated by DnaA at the transcriptional levels was dnaA. DnaA has been shown to regulate genes involved in a variety of cellular events including those that trigger sporulation, DNA repair, and cell cycle regulation. DnaA's dual functions (replication initiator and transcription factor) is a potential mechanism for DnaA to temporally coordinate diverse cellular events with the onset of chromosome replication. This strategy of using chromosome replication initiator proteins as regulators of gene expression has also been observed in archaea and eukaryotes. In this mini review, we focus on our current understanding of DnaA's transcriptional activity in various bacterial species.
Collapse
Affiliation(s)
- Inoka P Menikpurage
- Department of Microbiology, University of Illinois at Urbana-Champaign, Urbana, IL, United States
| | - Kristin Woo
- Department of Microbiology, University of Illinois at Urbana-Champaign, Urbana, IL, United States
| | - Paola E Mera
- Department of Microbiology, University of Illinois at Urbana-Champaign, Urbana, IL, United States
| |
Collapse
|
6
|
Schroeder K, Jonas K. The Protein Quality Control Network in Caulobacter crescentus. Front Mol Biosci 2021; 8:682967. [PMID: 33996917 PMCID: PMC8119881 DOI: 10.3389/fmolb.2021.682967] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2021] [Accepted: 04/08/2021] [Indexed: 11/13/2022] Open
Abstract
The asymmetric life cycle of Caulobacter crescentus has provided a model in which to study how protein quality control (PQC) networks interface with cell cycle and developmental processes, and how the functions of these systems change during exposure to stress. As in most bacteria, the PQC network of Caulobacter contains highly conserved ATP-dependent chaperones and proteases as well as more specialized holdases. During growth in optimal conditions, these systems support a regulated circuit of protein synthesis and degradation that drives cell differentiation and cell cycle progression. When stress conditions threaten the proteome, most components of the Caulobacter proteostasis network are upregulated and switch to survival functions that prevent, revert, and remove protein damage, while simultaneously pausing the cell cycle in order to regain protein homeostasis. The specialized physiology of Caulobacter influences how it copes with proteotoxic stress, such as in the global management of damaged proteins during recovery as well as in cell type-specific stress responses. Our mini-review highlights the discoveries that have been made in how Caulobacter utilizes its PQC network for regulating its life cycle under optimal and proteotoxic stress conditions, and discusses open research questions in this model.
Collapse
Affiliation(s)
- Kristen Schroeder
- Science for Life Laboratory, Department of Molecular Biosciences, The Wenner-Gren Institute, Stockholm University, Stockholm, Sweden
| | - Kristina Jonas
- Science for Life Laboratory, Department of Molecular Biosciences, The Wenner-Gren Institute, Stockholm University, Stockholm, Sweden
| |
Collapse
|
7
|
Multilayered control of chromosome replication in Caulobacter crescentus. Biochem Soc Trans 2019; 47:187-196. [PMID: 30626709 PMCID: PMC6393856 DOI: 10.1042/bst20180460] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2018] [Revised: 12/11/2018] [Accepted: 12/12/2018] [Indexed: 12/24/2022]
Abstract
The environmental Alphaproteobacterium Caulobacter crescentus is a classical model to study the regulation of the bacterial cell cycle. It divides asymmetrically, giving a stalked cell that immediately enters S phase and a swarmer cell that stays in the G1 phase until it differentiates into a stalked cell. Its genome consists in a single circular chromosome whose replication is tightly regulated so that it happens only in stalked cells and only once per cell cycle. Imbalances in chromosomal copy numbers are the most often highly deleterious, if not lethal. This review highlights recent discoveries on pathways that control chromosome replication when Caulobacter is exposed to optimal or less optimal growth conditions. Most of these pathways target two proteins that bind directly onto the chromosomal origin: the highly conserved DnaA initiator of DNA replication and the CtrA response regulator that is found in most Alphaproteobacteria The concerted inactivation and proteolysis of CtrA during the swarmer-to-stalked cell transition license cells to enter S phase, while a replisome-associated Regulated Inactivation and proteolysis of DnaA (RIDA) process ensures that initiation starts only once per cell cycle. When Caulobacter is stressed, it turns on control systems that delay the G1-to-S phase transition or the elongation of DNA replication, most probably increasing its fitness and adaptation capacities.
Collapse
|
8
|
Beroual W, Brilli M, Biondi EG. Non-coding RNAs Potentially Controlling Cell Cycle in the Model Caulobacter crescentus: A Bioinformatic Approach. Front Genet 2018; 9:164. [PMID: 29899753 PMCID: PMC5988900 DOI: 10.3389/fgene.2018.00164] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/12/2018] [Accepted: 04/23/2018] [Indexed: 11/13/2022] Open
Abstract
Caulobacter crescentus represents a remarkable model system to investigate global regulatory programs in bacteria. In particular, several decades of intensive study have revealed that its cell cycle is controlled by a cascade of master regulators, such as DnaA, GcrA, CcrM, and CtrA, that are responsible for the activation of functions required to progress through DNA replication, cell division and morphogenesis of polar structures (flagellum and stalk). In order to accomplish this task, several post-translational (phosphorylation and proteolysis) and transcriptional mechanisms are involved. Surprisingly, the role of non-coding RNAs (ncRNAs) in regulating the cell cycle has not been investigated. Here we describe a bioinformatic analysis that revealed that ncRNAs may well play a crucial role regulating cell cycle in C. crescentus. We used available prediction tools to understand which target genes may be regulated by ncRNAs in this bacterium. Furthermore, we predicted whether ncRNAs with a cell cycle regulated expression profile may be directly regulated by DnaA, GcrA, and CtrA, at the onset, during or end of the S-phase/swarmer cell, or if any of them has CcrM methylation sites in the promoter region. Our analysis suggests the existence of a potentially very important network of ncRNAs regulated by or regulating well-known cell cycle genes in C. crescentus. Our hypothesis is that ncRNAs are intimately connected to the known regulatory network, playing a crucial modulatory role in cell cycle progression.
Collapse
Affiliation(s)
- Wanassa Beroual
- Laboratoire de Chimie Bactérienne, Centre National de la Recherche Scientifique, Aix Marseille University, Marseille, France
| | - Matteo Brilli
- Department of Biosciences, Pediatric Clinical Research Center "Romeo ed Enrica Invernizzi, " University of Milan, Milan, Italy
| | - Emanuele G Biondi
- Laboratoire de Chimie Bactérienne, Centre National de la Recherche Scientifique, Aix Marseille University, Marseille, France
| |
Collapse
|
9
|
Felletti M, Omnus DJ, Jonas K. Regulation of the replication initiator DnaA in Caulobacter crescentus. BIOCHIMICA ET BIOPHYSICA ACTA-GENE REGULATORY MECHANISMS 2018; 1862:697-705. [PMID: 29382570 DOI: 10.1016/j.bbagrm.2018.01.004] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/28/2017] [Accepted: 01/10/2018] [Indexed: 11/18/2022]
Abstract
The decision to initiate DNA replication is a critical step in the cell cycle of all organisms. In nearly all bacteria, replication initiation requires the activity of the conserved replication initiation protein DnaA. Due to its central role in cell cycle progression, DnaA activity must be precisely regulated. This review summarizes the current state of DnaA regulation in the asymmetrically dividing α-proteobacterium Caulobacter crescentus, an important model for bacterial cell cycle studies. Mechanisms will be discussed that regulate DnaA activity and abundance under optimal conditions and in coordination with the asymmetric Caulobacter cell cycle. Furthermore, we highlight recent findings of how regulated DnaA synthesis and degradation collaborate to adjust DnaA abundance under stress conditions. The mechanisms described provide important examples of how DNA replication is regulated in an α-proteobacterium and thus represent an important starting point for the study of DNA replication in many other bacteria. This article is part of a Special Issue entitled: Dynamic gene expression, edited by Prof. Patrick Viollier.
Collapse
Affiliation(s)
- Michele Felletti
- Science for Life Laboratory, Department of Molecular Biosciences, The Wenner-Gren Institute, Stockholm University, 10691 Stockholm, Sweden
| | - Deike J Omnus
- Science for Life Laboratory, Department of Molecular Biosciences, The Wenner-Gren Institute, Stockholm University, 10691 Stockholm, Sweden
| | - Kristina Jonas
- Science for Life Laboratory, Department of Molecular Biosciences, The Wenner-Gren Institute, Stockholm University, 10691 Stockholm, Sweden.
| |
Collapse
|
10
|
Leslie DJ, Heinen C, Schramm FD, Thüring M, Aakre CD, Murray SM, Laub MT, Jonas K. Nutritional Control of DNA Replication Initiation through the Proteolysis and Regulated Translation of DnaA. PLoS Genet 2015; 11:e1005342. [PMID: 26134530 PMCID: PMC4489657 DOI: 10.1371/journal.pgen.1005342] [Citation(s) in RCA: 51] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2015] [Accepted: 06/08/2015] [Indexed: 11/18/2022] Open
Abstract
Bacteria can arrest their own growth and proliferation upon nutrient depletion and under various stressful conditions to ensure their survival. However, the molecular mechanisms responsible for suppressing growth and arresting the cell cycle under such conditions remain incompletely understood. Here, we identify post-transcriptional mechanisms that help enforce a cell-cycle arrest in Caulobacter crescentus following nutrient limitation and during entry into stationary phase by limiting the accumulation of DnaA, the conserved replication initiator protein. DnaA is rapidly degraded by the Lon protease following nutrient limitation. However, the rate of DnaA degradation is not significantly altered by changes in nutrient availability. Instead, we demonstrate that decreased nutrient availability downregulates dnaA translation by a mechanism involving the 5' untranslated leader region of the dnaA transcript; Lon-dependent proteolysis of DnaA then outpaces synthesis, leading to the elimination of DnaA and the arrest of DNA replication. Our results demonstrate how regulated translation and constitutive degradation provide cells a means of precisely and rapidly modulating the concentration of key regulatory proteins in response to environmental inputs. The duplication of genetic material is a prerequisite for cellular growth and proliferation. Under optimal growth conditions, when cells strive to grow and divide, DNA replication must be initiated with high frequency. However, under nutrient limiting conditions cells stop initiating DNA replication to ensure cellular integrity. Here, we identify mechanisms responsible for blocking DNA replication initiation under nutrient limitation in Caulobacter crescentus. In this bacterium nutrient limitation results in a strong downregulation of DnaA, the conserved replication initiator protein, which is required for DNA replication in nearly all bacteria. Our data demonstrate that the downregulation of DnaA depends on a reduction in DnaA synthesis in combination with fast degradation by the protease Lon. The changes in DnaA synthesis are mediated by a post-transcriptional mechanism, which adjusts DnaA translation in response to nutrient availability. The constitutively high rate of DnaA degradation then ensures the rapid clearance of the protein following the changes in translation. Our work exemplifies how regulated protein synthesis and fast degradation of key regulatory proteins allow for the precise and dynamic control of important cellular processes in response to environmental changes.
Collapse
Affiliation(s)
- David J. Leslie
- LOEWE Center for Synthetic Microbiology, Philipps University Marburg, Marburg, Germany
- Max Planck Institute for Terrestrial Microbiology, Marburg, Germany
| | - Christian Heinen
- LOEWE Center for Synthetic Microbiology, Philipps University Marburg, Marburg, Germany
- Max Planck Institute for Terrestrial Microbiology, Marburg, Germany
| | - Frederic D. Schramm
- LOEWE Center for Synthetic Microbiology, Philipps University Marburg, Marburg, Germany
| | - Marietta Thüring
- LOEWE Center for Synthetic Microbiology, Philipps University Marburg, Marburg, Germany
| | - Christopher D. Aakre
- Department of Biology, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States of America
| | - Sean M. Murray
- LOEWE Center for Synthetic Microbiology, Philipps University Marburg, Marburg, Germany
- Max Planck Institute for Terrestrial Microbiology, Marburg, Germany
| | - Michael T. Laub
- Department of Biology, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States of America
- Howard Hughes Medical Institute, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States of America
| | - Kristina Jonas
- LOEWE Center for Synthetic Microbiology, Philipps University Marburg, Marburg, Germany
- Department of Biology, Philipps University Marburg, Marburg, Germany
- * E-mail:
| |
Collapse
|
11
|
DNA methylation in Caulobacter and other Alphaproteobacteria during cell cycle progression. Trends Microbiol 2014; 22:528-35. [DOI: 10.1016/j.tim.2014.05.003] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/12/2014] [Revised: 05/07/2014] [Accepted: 05/08/2014] [Indexed: 01/20/2023]
|
12
|
Schrader JM, Zhou B, Li GW, Lasker K, Childers WS, Williams B, Long T, Crosson S, McAdams HH, Weissman JS, Shapiro L. The coding and noncoding architecture of the Caulobacter crescentus genome. PLoS Genet 2014; 10:e1004463. [PMID: 25078267 PMCID: PMC4117421 DOI: 10.1371/journal.pgen.1004463] [Citation(s) in RCA: 101] [Impact Index Per Article: 10.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2014] [Accepted: 05/13/2014] [Indexed: 11/24/2022] Open
Abstract
Caulobacter crescentus undergoes an asymmetric cell division controlled by a genetic circuit that cycles in space and time. We provide a universal strategy for defining the coding potential of bacterial genomes by applying ribosome profiling, RNA-seq, global 5′-RACE, and liquid chromatography coupled with tandem mass spectrometry (LC-MS) data to the 4-megabase C. crescentus genome. We mapped transcript units at single base-pair resolution using RNA-seq together with global 5′-RACE. Additionally, using ribosome profiling and LC-MS, we mapped translation start sites and coding regions with near complete coverage. We found most start codons lacked corresponding Shine-Dalgarno sites although ribosomes were observed to pause at internal Shine-Dalgarno sites within the coding DNA sequence (CDS). These data suggest a more prevalent use of the Shine-Dalgarno sequence for ribosome pausing rather than translation initiation in C. crescentus. Overall 19% of the transcribed and translated genomic elements were newly identified or significantly improved by this approach, providing a valuable genomic resource to elucidate the complete C. crescentus genetic circuitry that controls asymmetric cell division. Caulobacter crescentus is a model system for studying asymmetric cell division, a fundamental process that, through differential gene expression in the two daughter cells, enables the generation of cells with different fates. To explore how the genome directs and maintains asymmetry upon cell division, we performed a coordinated analysis of multiple genomic and proteomic datasets to identify the RNA and protein coding features in the C. crescentus genome. Our integrated analysis identifies many new genetic regulatory elements, adding significant regulatory complexity to the C. crescentus genome. Surprisingly, 75.4% of protein coding genes lack a canonical translation initiation sequence motif (the Shine-Dalgarno site) which hybridizes to the 3′ end of the ribosomal RNA allowing translation initiation. We find Shine-Dalgarno sites primarily inside of genes where they cause translating ribosomes to pause, possibly allowing nascent proteins to correctly fold. With our detailed map of genomic transcription and translation elements, a systems view of the genetic network that controls asymmetric cell division is within reach.
Collapse
Affiliation(s)
- Jared M. Schrader
- Department of Developmental Biology, Stanford University, Stanford, California, United States of America
| | - Bo Zhou
- Department of Developmental Biology, Stanford University, Stanford, California, United States of America
| | - Gene-Wei Li
- Department of Cellular and Molecular Pharmacology, California Institute of Quantitative Biology, Center for RNA Systems Biology, Howard Hughes Medical Institute, University of California, San Francisco, San Francisco, California, United States of America
| | - Keren Lasker
- Department of Developmental Biology, Stanford University, Stanford, California, United States of America
| | - W. Seth Childers
- Department of Developmental Biology, Stanford University, Stanford, California, United States of America
| | - Brandon Williams
- Department of Developmental Biology, Stanford University, Stanford, California, United States of America
| | - Tao Long
- Department of Developmental Biology, Stanford University, Stanford, California, United States of America
| | - Sean Crosson
- Department of Biochemistry and Molecular Biology, University of Chicago, Chicago, Illinois, United States of America
| | - Harley H. McAdams
- Department of Developmental Biology, Stanford University, Stanford, California, United States of America
| | - Jonathan S. Weissman
- Department of Cellular and Molecular Pharmacology, California Institute of Quantitative Biology, Center for RNA Systems Biology, Howard Hughes Medical Institute, University of California, San Francisco, San Francisco, California, United States of America
| | - Lucy Shapiro
- Department of Developmental Biology, Stanford University, Stanford, California, United States of America
- * E-mail:
| |
Collapse
|
13
|
Murray SM, Panis G, Fumeaux C, Viollier PH, Howard M. Computational and genetic reduction of a cell cycle to its simplest, primordial components. PLoS Biol 2013; 11:e1001749. [PMID: 24415923 PMCID: PMC3885167 DOI: 10.1371/journal.pbio.1001749] [Citation(s) in RCA: 54] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2013] [Accepted: 11/14/2013] [Indexed: 02/02/2023] Open
Abstract
What are the minimal requirements to sustain an asymmetric cell cycle? Here we use mathematical modelling and forward genetics to reduce an asymmetric cell cycle to its simplest, primordial components. In the Alphaproteobacterium Caulobacter crescentus, cell cycle progression is believed to be controlled by a cyclical genetic circuit comprising four essential master regulators. Unexpectedly, our in silico modelling predicted that one of these regulators, GcrA, is in fact dispensable. We confirmed this experimentally, finding that ΔgcrA cells are viable, but slow-growing and elongated, with the latter mostly due to an insufficiency of a key cell division protein. Furthermore, suppressor analysis showed that another cell cycle regulator, the methyltransferase CcrM, is similarly dispensable with simultaneous gcrA/ccrM disruption ameliorating the cytokinetic and growth defect of ΔgcrA cells. Within the Alphaproteobacteria, gcrA and ccrM are consistently present or absent together, rather than either gene being present alone, suggesting that gcrA/ccrM constitutes an independent, dispensable genetic module. Together our approaches unveil the essential elements of a primordial asymmetric cell cycle that should help illuminate more complex cell cycles.
Collapse
Affiliation(s)
- Seán M. Murray
- Computational and Systems Biology, John Innes Centre, Norwich Research Park, Norwich, United Kingdom
| | - Gaël Panis
- Department of Microbiology & Molecular Medicine, Institute of Genetics & Genomics in Geneva (iGE3), Faculty of Medicine/CMU, University of Geneva, Geneva, Switzerland
| | - Coralie Fumeaux
- Department of Microbiology & Molecular Medicine, Institute of Genetics & Genomics in Geneva (iGE3), Faculty of Medicine/CMU, University of Geneva, Geneva, Switzerland
| | - Patrick H. Viollier
- Department of Microbiology & Molecular Medicine, Institute of Genetics & Genomics in Geneva (iGE3), Faculty of Medicine/CMU, University of Geneva, Geneva, Switzerland
- * E-mail: (P.H.V.); (M.H.)
| | - Martin Howard
- Computational and Systems Biology, John Innes Centre, Norwich Research Park, Norwich, United Kingdom
- * E-mail: (P.H.V.); (M.H.)
| |
Collapse
|
14
|
Wegrzyn K, Witosinska M, Schweiger P, Bury K, Jenal U, Konieczny I. RK2 plasmid dynamics in Caulobacter crescentus cells--two modes of DNA replication initiation. MICROBIOLOGY-SGM 2013; 159:1010-1022. [PMID: 23538715 DOI: 10.1099/mic.0.065490-0] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Abstract
Undisturbed plasmid dynamics is required for the stable maintenance of plasmid DNA in bacterial cells. In this work, we analysed subcellular localization, DNA synthesis and nucleoprotein complex formation of plasmid RK2 during the cell cycle of Caulobacter crescentus. Our microscopic observations showed asymmetrical distribution of plasmid RK2 foci between the two compartments of Caulobacter predivisional cells, resulting in asymmetrical allocation of plasmids to progeny cells. Moreover, using a quantitative PCR (qPCR) method, we estimated that multiple plasmid particles form a single fluorescent focus and that the number of plasmids per focus is approximately equal in both swarmer and predivisional Caulobacter cells. Analysis of the dynamics of TrfA-oriV complex formation during the Caulobacter cell cycle revealed that TrfA binds oriV primarily during the G1 phase, however, plasmid DNA synthesis occurs during the S and G2 phases of the Caulobacter cell cycle. Both in vitro and in vivo analysis of RK2 replication initiation in C. crescentus cells demonstrated that it is independent of the Caulobacter DnaA protein in the presence of the longer version of TrfA protein, TrfA-44. However, in vivo stability tests of plasmid RK2 derivatives suggested that a DnaA-dependent mode of plasmid replication initiation is also possible.
Collapse
Affiliation(s)
- Katarzyna Wegrzyn
- Department of Molecular and Cellular Biology, Intercollegiate Faculty of Biotechnology, University of Gdansk, ul. Kladki 24, 80-822 Gdansk, Poland
| | - Monika Witosinska
- Department of Molecular and Cellular Biology, Intercollegiate Faculty of Biotechnology, University of Gdansk, ul. Kladki 24, 80-822 Gdansk, Poland
| | - Pawel Schweiger
- Department of Molecular and Cellular Biology, Intercollegiate Faculty of Biotechnology, University of Gdansk, ul. Kladki 24, 80-822 Gdansk, Poland
| | - Katarzyna Bury
- Department of Molecular and Cellular Biology, Intercollegiate Faculty of Biotechnology, University of Gdansk, ul. Kladki 24, 80-822 Gdansk, Poland
| | - Urs Jenal
- Center for Molecular Life Sciences, University of Basel, Klingelbergstrasse 50/70, CH-4056 Basel, Switzerland
| | - Igor Konieczny
- Department of Molecular and Cellular Biology, Intercollegiate Faculty of Biotechnology, University of Gdansk, ul. Kladki 24, 80-822 Gdansk, Poland
| |
Collapse
|
15
|
Janssen BD, Hayes CS. The tmRNA ribosome-rescue system. ADVANCES IN PROTEIN CHEMISTRY AND STRUCTURAL BIOLOGY 2012; 86:151-91. [PMID: 22243584 DOI: 10.1016/b978-0-12-386497-0.00005-0] [Citation(s) in RCA: 97] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
The bacterial tmRNA quality control system monitors protein synthesis and recycles stalled translation complexes in a process termed "ribosome rescue." During rescue, tmRNA acts first as a transfer RNA to bind stalled ribosomes, then as a messenger RNA to add the ssrA peptide tag to the C-terminus of the nascent polypeptide chain. The ssrA peptide targets tagged peptides for proteolysis, ensuring rapid degradation of potentially deleterious truncated polypeptides. Ribosome rescue also facilitates turnover of the damaged messages responsible for translational arrest. Thus, tmRNA increases the fidelity of gene expression by promoting the synthesis of full-length proteins. In addition to serving as a global quality control system, tmRNA also plays important roles in bacterial development, pathogenesis, and environmental stress responses. This review focuses on the mechanism of tmRNA-mediated ribosome rescue and the role of tmRNA in bacterial physiology.
Collapse
Affiliation(s)
- Brian D Janssen
- Department of Molecular, Cellular and Developmental Biology, University of California, Santa Barbara, California, USA
| | | |
Collapse
|
16
|
Collier J. Regulation of chromosomal replication in Caulobacter crescentus. Plasmid 2011; 67:76-87. [PMID: 22227374 DOI: 10.1016/j.plasmid.2011.12.007] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/27/2011] [Revised: 12/19/2011] [Accepted: 12/21/2011] [Indexed: 01/12/2023]
Abstract
The alpha-proteobacterium Caulobacter crescentus is characterized by its asymmetric cell division, which gives rise to a replicating stalked cell and a non-replicating swarmer cell. Thus, the initiation of chromosomal replication is tightly regulated, temporally and spatially, to ensure that it is coordinated with cell differentiation and cell cycle progression. Waves of DnaA and CtrA activities control when and where the initiation of DNA replication will take place in C. crescentus cells. The conserved DnaA protein initiates chromosomal replication by directly binding to sites within the chromosomal origin (Cori), ensuring that DNA replication starts once and only once per cell cycle. The CtrA response regulator represses the initiation of DNA replication in swarmer cells and in the swarmer compartment of pre-divisional cells, probably by competing with DnaA for binding to Cori. CtrA and DnaA are controlled by multiple redundant regulatory pathways that include DNA methylation-dependent transcriptional regulation, temporally regulated proteolysis and the targeting of regulators to specific locations within the cell. Besides being critical regulators of chromosomal replication, CtrA and DnaA are also master transcriptional regulators that control the expression of many genes, thus connecting DNA replication with other events of the C. crescentus cell cycle.
Collapse
Affiliation(s)
- Justine Collier
- Department of Fundamental Microbiology, Faculty of Biology and Medicine, University of Lausanne, Quartier UNIL/Sorge, Lausanne, CH 1015, Switzerland.
| |
Collapse
|
17
|
Bacterial small RNA regulators: versatile roles and rapidly evolving variations. Cold Spring Harb Perspect Biol 2011; 3:cshperspect.a003798. [PMID: 20980440 DOI: 10.1101/cshperspect.a003798] [Citation(s) in RCA: 538] [Impact Index Per Article: 41.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
Small RNA regulators (sRNAs) have been identified in a wide range of bacteria and found to play critical regulatory roles in many processes. The major families of sRNAs include true antisense RNAs, synthesized from the strand complementary to the mRNA they regulate, sRNAs that also act by pairing but have limited complementarity with their targets, and sRNAs that regulate proteins by binding to and affecting protein activity. The sRNAs with limited complementarity are akin to eukaryotic microRNAs in their ability to modulate the activity and stability of multiple mRNAs. In many bacterial species, the RNA chaperone Hfq is required to promote pairing between these sRNAs and their target mRNAs. Understanding the evolution of regulatory sRNAs remains a challenge; sRNA genes show evidence of duplication and horizontal transfer but also could be evolved from tRNAs, mRNAs or random transcription.
Collapse
|
18
|
Kirkpatrick CL, Viollier PH. Decoding Caulobacter development. FEMS Microbiol Rev 2011; 36:193-205. [PMID: 22091823 DOI: 10.1111/j.1574-6976.2011.00309.x] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2011] [Revised: 09/15/2011] [Accepted: 09/15/2011] [Indexed: 11/27/2022] Open
Abstract
Caulobacter crescentus uses a multi-layered system of oscillating regulators to program different developmental fates into each daughter cell at division. This is achieved by superimposing gene expression, subcellular localization, phosphorylation, and regulated proteolysis to form a complex regulatory network that integrates chromosome replication, segregation, polar differentiation, and cytokinesis. In this review, we outline the current state of research in the field of Caulobacter development, emphasizing new findings that elaborate how the developmental program is modulated by factors such as the environment or the metabolic state of the cell.
Collapse
Affiliation(s)
- Clare L Kirkpatrick
- Department of Microbiology and Molecular Medicine, University of Geneva, Geneva, Switzerland
| | | |
Collapse
|
19
|
Fernandez-Fernandez C, Gonzalez D, Collier J. Regulation of the activity of the dual-function DnaA protein in Caulobacter crescentus. PLoS One 2011; 6:e26028. [PMID: 22022497 PMCID: PMC3193534 DOI: 10.1371/journal.pone.0026028] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2011] [Accepted: 09/15/2011] [Indexed: 12/05/2022] Open
Abstract
DnaA is a conserved essential bacterial protein that acts as the initiator of chromosomal replication as well as a master transcriptional regulator in Caulobacter crescentus. Thus, the intracellular levels of active DnaA need to be tightly regulated during the cell cycle. Our previous work suggested that DnaA may be regulated at the level of its activity by the replisome-associated protein HdaA. Here, we describe the construction of a mutant DnaA protein [DnaA(R357A)]. The R357 residue in the AAA+ domain of the C. crescentus DnaA protein is equivalent to the R334 residue of the E. coli DnaA protein, which is required for the Regulatory Inactivation of DnaA (RIDA). We found that the expression of the DnaA(R357A) mutant protein in C. crescentus, but not the expression of the wild-type DnaA protein at similar levels, causes a severe phenotype of over-initiation of chromosomal replication and that it blocks cell division. Thus, the mutant DnaA(R357A) protein is hyper-active to promote the initiation of DNA replication, compared to the wild-type DnaA protein. DnaA(R357A) could not replace DnaA in vivo, indicating that the switch in DnaA activity once chromosomal replication has started may be an essential process in C. crescentus. We propose that the inactivation of DnaA is the main mechanism ensuring that chromosomal replication starts only once per cell cycle. We further observed that the R357A substitution in DnaA does not promote the activity of DnaA as a direct transcriptional activator of four important genes, encoding HdaA, the GcrA master cell cycle regulator, the FtsZ cell division protein and the MipZ spatial regulator of cell division. Thus, the AAA+ domain of DnaA may play a role in temporally regulating the bifunctionality of DnaA by reallocating DnaA molecules from initiating DNA replication to transcribing genes within the unique DnaA regulon of C. crescentus.
Collapse
Affiliation(s)
- Carmen Fernandez-Fernandez
- Department of Fundamental Microbiology, Faculty of Biology and Medicine, University of Lausanne, Lausanne, Switzerland
| | - Diego Gonzalez
- Department of Fundamental Microbiology, Faculty of Biology and Medicine, University of Lausanne, Lausanne, Switzerland
| | - Justine Collier
- Department of Fundamental Microbiology, Faculty of Biology and Medicine, University of Lausanne, Lausanne, Switzerland
- * E-mail:
| |
Collapse
|
20
|
Modularity of the bacterial cell cycle enables independent spatial and temporal control of DNA replication. Curr Biol 2011; 21:1092-101. [PMID: 21683595 DOI: 10.1016/j.cub.2011.05.040] [Citation(s) in RCA: 62] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2011] [Revised: 04/26/2011] [Accepted: 05/23/2011] [Indexed: 11/21/2022]
Abstract
BACKGROUND Complex regulatory circuits in biology are often built of simpler subcircuits or modules. In most cases, the functional consequences and evolutionary origins of modularity remain poorly defined. RESULTS Here, by combining single-cell microscopy with genetic approaches, we demonstrate that two separable modules independently govern the temporal and spatial control of DNA replication in the asymmetrically dividing bacterium Caulobacter crescentus. DNA replication control involves DnaA, which promotes initiation, and CtrA, which silences initiation. We show that oscillations in DnaA activity dictate the periodicity of replication while CtrA governs the asymmetric replicative fates of daughter cells. Importantly, we demonstrate that DnaA activity oscillates independently of CtrA. CONCLUSIONS The genetic separability of spatial and temporal control modules in Caulobacter reflects their evolutionary history. DnaA is the central component of an ancient and phylogenetically widespread circuit that governs replication periodicity in Caulobacter and most other bacteria. By contrast, CtrA, which is found only in the asymmetrically dividing α-proteobacteria, was integrated later in evolution to enforce replicative asymmetry on daughter cells.
Collapse
|
21
|
Collins LJ. The RNA infrastructure: an introduction to ncRNA networks. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2011; 722:1-19. [PMID: 21915779 DOI: 10.1007/978-1-4614-0332-6_1] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
The RNA infrastructure connects RNA-based functions. With transcription-to-translation processing forming the core of the network, we can visualise how RNA-based regulation, cleavage and modification are the backbone of cellular function. The key to interpreting the RNA-infrastructure is in understanding how core RNAs (tRNA, mRNA and rRNA) and other ncRNAs operate in a spatial-temporal manner, moving around the nucleus, cytoplasm and organelles during processing, or in response to environmental cues. This chapter summarises the concept of the RNA-infrastructure, and highlights examples of RNA-based networking within prokaryotes and eukaryotes. It describes how transcription-to-translation processes are tightly connected, and explores some similarities and differences between prokaryotic and eukaryotic RNA networking.
Collapse
Affiliation(s)
- Lesley J Collins
- Institute of Fundamental Sciences, Massey University, Palmerston North, New Zealand.
| |
Collapse
|
22
|
Barends S, Kraal B, van Wezel GP. The tmRNA-tagging mechanism and the control of gene expression: a review. WILEY INTERDISCIPLINARY REVIEWS-RNA 2010; 2:233-46. [PMID: 21957008 DOI: 10.1002/wrna.48] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
The tmRNA-mediated trans-translation system is a unique quality control system in eubacteria that combines translational surveillance with the rescue of stalled ribosomes. During trans-translation, the chimeric tmRNA molecule--which acts as both tRNA and mRNA--is delivered to the ribosomal A site by a ribonucleoprotein complex of SmpB and EF-Tu-GTP, allowing the stalled ribosome to switch template and resume translation on a small coding sequence inside the tmRNA molecule. As a result, the aberrant protein becomes tagged by a sequence that is a target for proteolytic degradation. Thus, the system elegantly combines ribosome recycling with a clean-up function when triggered by truncated transcripts or rare codons. In addition, recent observations point to a specific regulation of the translation of a small number of genes by tmRNA-mediated inhibition or stimulation. In this review, we discuss the most prominent biochemical and structural aspects of trans-translation and then focus on the specific role of tmRNA in stress management and cell-cycle control of morphologically complex bacteria.
Collapse
Affiliation(s)
- Sharief Barends
- ProteoNic, Niels Bohrweg 11-13, 2333 CA Leiden, The Netherlands
| | | | | |
Collapse
|
23
|
Kärkkäinen PM, Valkonen M, Hyvärinen A, Nevalainen A, Rintala H. Determination of bacterial load in house dust using qPCR, chemical markers and culture. ACTA ACUST UNITED AC 2010; 12:759-68. [DOI: 10.1039/b917937b] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
|
24
|
Epigenetic regulation of the bacterial cell cycle. Curr Opin Microbiol 2009; 12:722-9. [PMID: 19783470 DOI: 10.1016/j.mib.2009.08.005] [Citation(s) in RCA: 58] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2009] [Accepted: 08/16/2009] [Indexed: 01/15/2023]
Abstract
N(6)-methyl-adenines can serve as epigenetic signals for interactions between regulatory DNA sequences and regulatory proteins that control cellular functions, such as the initiation of chromosome replication or the expression of specific genes. Several of these genes encode master regulators of the bacterial cell cycle. DNA adenine methylation is mediated by Dam in gamma-proteobacteria and by CcrM in alpha-proteobacteria. A major difference between them is that CcrM is cell cycle regulated, while Dam is active throughout the cell cycle. In alpha-proteobacteria, GANTC sites can remain hemi-methylated for a significant period of the cell cycle, depending on their location on the chromosome. In gamma-proteobacteria, most GATC sites are only transiently hemi-methylated, except regulatory GATC sites that are protected from Dam methylation by specific DNA-binding proteins.
Collapse
|
25
|
The role of proteolysis in the Caulobacter crescentus cell cycle and development. Res Microbiol 2009; 160:687-95. [PMID: 19781638 DOI: 10.1016/j.resmic.2009.09.006] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2009] [Revised: 09/03/2009] [Accepted: 09/04/2009] [Indexed: 11/23/2022]
Abstract
Caulobacter crescentus cell cycle progression is implemented by oscillating global transcriptional regulators that establish temporal and spatial control of modular genetic subsystems during the cell cycle. The hierarchy of this regulatory circuit is established through a combination of gene expression control and regulated proteolysis. Recent results highlight the importance of spatial organization for controlled proteolysis in C. crescentus.
Collapse
|