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Kohiyama M, Herrick J, Norris V. Open Questions about the Roles of DnaA, Related Proteins, and Hyperstructure Dynamics in the Cell Cycle. Life (Basel) 2023; 13:1890. [PMID: 37763294 PMCID: PMC10532879 DOI: 10.3390/life13091890] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2023] [Revised: 08/29/2023] [Accepted: 09/06/2023] [Indexed: 09/29/2023] Open
Abstract
The DnaA protein has long been considered to play the key role in the initiation of chromosome replication in modern bacteria. Many questions about this role, however, remain unanswered. Here, we raise these questions within a framework based on the dynamics of hyperstructures, alias large assemblies of molecules and macromolecules that perform a function. In these dynamics, hyperstructures can (1) emit and receive signals or (2) fuse and separate from one another. We ask whether the DnaA-based initiation hyperstructure acts as a logic gate receiving information from the membrane, the chromosome, and metabolism to trigger replication; we try to phrase some of these questions in terms of DNA supercoiling, strand opening, glycolytic enzymes, SeqA, ribonucleotide reductase, the macromolecular synthesis operon, post-translational modifications, and metabolic pools. Finally, we ask whether, underpinning the regulation of the cell cycle, there is a physico-chemical clock inherited from the first protocells, and whether this clock emits a single signal that triggers both chromosome replication and cell division.
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Affiliation(s)
- Masamichi Kohiyama
- Institut Jacques Monod, Université Paris Cité, CNRS, 75013 Paris, France;
| | - John Herrick
- Independent Researcher, 3 rue des Jeûneurs, 75002 Paris, France;
| | - Vic Norris
- CBSA UR 4312, University of Rouen Normandy, University of Caen Normandy, Normandy University, 76000 Rouen, France
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Miyoshi K, Tatsumoto Y, Ozaki S, Katayama T. Negative feedback for DARS2-Fis complex by ATP-DnaA supports the cell cycle-coordinated regulation for chromosome replication. Nucleic Acids Res 2021; 49:12820-12835. [PMID: 34871419 PMCID: PMC8682772 DOI: 10.1093/nar/gkab1171] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2021] [Revised: 11/05/2021] [Accepted: 11/11/2021] [Indexed: 11/13/2022] Open
Abstract
In Escherichia coli, the replication initiator DnaA oscillates between an ATP- and an ADP-bound state in a cell cycle-dependent manner, supporting regulation for chromosome replication. ATP-DnaA cooperatively assembles on the replication origin using clusters of low-affinity DnaA-binding sites. After initiation, DnaA-bound ATP is hydrolyzed, producing initiation-inactive ADP-DnaA. For the next round of initiation, ADP-DnaA binds to the chromosomal locus DARS2, which promotes the release of ADP, yielding the apo-DnaA to regain the initiation activity through ATP binding. This DnaA reactivation by DARS2 depends on site-specific binding of IHF (integration host factor) and Fis proteins and IHF binding to DARS2 occurs specifically during pre-initiation. Here, we reveal that Fis binds to an essential region in DARS2 specifically during pre-initiation. Further analyses demonstrate that ATP-DnaA, but not ADP-DnaA, oligomerizes on a cluster of low-affinity DnaA-binding sites overlapping the Fis-binding region, which competitively inhibits Fis binding and hence the DARS2 activity. DiaA (DnaA initiator-associating protein) stimulating ATP-DnaA assembly enhances the dissociation of Fis. These observations lead to a negative feedback model where the activity of DARS2 is repressed around the time of initiation by the elevated ATP-DnaA level and is stimulated following initiation when the ATP-DnaA level is reduced.
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Affiliation(s)
- Kenya Miyoshi
- Department of Molecular Biology, Kyushu University Graduate School of Pharmaceutical Sciences, Fukuoka 812-8582, Japan
| | - Yuka Tatsumoto
- Department of Molecular Biology, Kyushu University Graduate School of Pharmaceutical Sciences, Fukuoka 812-8582, Japan
| | - Shogo Ozaki
- Department of Molecular Biology, Kyushu University Graduate School of Pharmaceutical Sciences, Fukuoka 812-8582, Japan
| | - Tsutomu Katayama
- Department of Molecular Biology, Kyushu University Graduate School of Pharmaceutical Sciences, Fukuoka 812-8582, Japan
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Elevated Levels of the Escherichia coli nrdAB-Encoded Ribonucleotide Reductase Counteract the Toxicity Caused by an Increased Abundance of the β Clamp. J Bacteriol 2021; 203:e0030421. [PMID: 34543109 DOI: 10.1128/jb.00304-21] [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] [Indexed: 01/27/2023] Open
Abstract
Expression of the Escherichia coli dnaN-encoded β clamp at ≥10-fold higher than chromosomally expressed levels impedes growth by interfering with DNA replication. A mutant clamp (βE202K bearing a glutamic acid-to-lysine substitution at residue 202) binds to DNA polymerase III (Pol III) with higher affinity than the wild-type clamp, suggesting that its failure to impede growth is independent of its ability to sequester Pol III away from the replication fork. Our results demonstrate that the dnaNE202K strain underinitiates DNA replication due to insufficient levels of DnaA-ATP and expresses several DnaA-regulated genes at altered levels, including nrdAB, that encode the class 1a ribonucleotide reductase (RNR). Elevated expression of nrdAB was dependent on hda function. As the β clamp-Hda complex regulates the activity of DnaA by stimulating its intrinsic ATPase activity, this finding suggests that the dnaNE202K allele supports an elevated level of Hda activity in vivo compared with the wild-type strain. In contrast, using an in vitro assay reconstituted with purified components the βE202K and wild-type clamp proteins supported comparable levels of Hda activity. Nevertheless, co-overexpression of the nrdAB-encoded RNR relieved the growth defect caused by elevated levels of the β clamp. These results support a model in which increased cellular levels of DNA precursors relieve the ability of elevated β clamp levels to impede growth and suggest either that multiple effects stemming from the dnaNE202K mutation contribute to elevated nrdAB levels or that Hda plays a noncatalytic role in regulating DnaA-ATP by sequestering it to reduce its availability. IMPORTANCE DnaA bound to ATP acts in initiation of DNA replication and regulates the expression of several genes whose products act in DNA metabolism. The state of the ATP bound to DnaA is regulated in part by the β clamp-Hda complex. The dnaNE202K allele was identified by virtue of its inability to impede growth when expressed ≥10-fold higher than chromosomally expressed levels. While the dnaNE202K strain exhibits several phenotypes consistent with heightened Hda activity, the wild-type and βE202K clamp proteins support equivalent levels of Hda activity in vitro. Taken together, these results suggest that βE202K-Hda plays a noncatalytic role in regulating DnaA-ATP. This, as well as alternative models, is discussed.
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The Mutant β E202K Sliding Clamp Protein Impairs DNA Polymerase III Replication Activity. J Bacteriol 2021; 203:e0030321. [PMID: 34543108 DOI: 10.1128/jb.00303-21] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023] Open
Abstract
Expression of the Escherichia coli dnaN-encoded β clamp at ≥10-fold higher than chromosomally expressed levels impedes growth by interfering with DNA replication. We hypothesized that the excess β clamp sequesters the replicative DNA polymerase III (Pol III) to inhibit replication. As a test of this hypothesis, we obtained eight mutant clamps with an inability to impede growth and measured their ability to stimulate Pol III replication in vitro. Compared with the wild-type clamp, seven of the mutants were defective, consistent with their elevated cellular levels failing to sequester Pol III. However, the βE202K mutant that bears a glutamic acid-to-lysine substitution at residue 202 displayed an increased affinity for Pol IIIα and Pol III core (Pol IIIαεθ), suggesting that it could still sequester Pol III effectively. Of interest, βE202K supported in vitro DNA replication by Pol II and Pol IV but was defective with Pol III. Genetic experiments indicated that the dnaNE202K strain remained proficient in DNA damage-induced mutagenesis but was induced modestly for SOS and displayed sensitivity to UV light and methyl methanesulfonate. These results correlate an impaired ability of the mutant βE202K clamp to support Pol III replication in vivo with its in vitro defect in DNA replication. Taken together, our results (i) support the model that sequestration of Pol III contributes to growth inhibition, (ii) argue for the existence of an additional mechanism that contributes to lethality, and (iii) suggest that physical and functional interactions of the β clamp with Pol III are more extensive than appreciated currently. IMPORTANCE The β clamp plays critically important roles in managing the actions of multiple proteins at the replication fork. However, we lack a molecular understanding of both how the clamp interacts with these different partners and the mechanisms by which it manages their respective actions. We previously exploited the finding that an elevated cellular level of the β clamp impedes Escherichia coli growth by interfering with DNA replication. Using a genetic selection method, we obtained novel mutant β clamps that fail to inhibit growth. Their analysis revealed that βE202K is unique among them. Our work offers new insights into how the β clamp interacts with and manages the actions of E. coli DNA polymerases II, III, and IV.
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Wozniak KJ, Simmons LA. Hydroxyurea Induces a Stress Response That Alters DNA Replication and Nucleotide Metabolism in Bacillus subtilis. J Bacteriol 2021; 203:e0017121. [PMID: 34031038 PMCID: PMC8407345 DOI: 10.1128/jb.00171-21] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2021] [Accepted: 05/12/2021] [Indexed: 12/12/2022] Open
Abstract
Hydroxyurea (HU) is classified as a ribonucleotide reductase (RNR) inhibitor and has been widely used to stall DNA replication by depleting deoxyribonucleoside triphosphate (dNTP) pools. Recent evidence in Escherichia coli shows that HU readily forms breakdown products that damage DNA directly, indicating that toxicity is a result of secondary effects. Because HU is so widely used in the laboratory and as a clinical therapeutic, it is important to understand its biological effects. To determine how Bacillus subtilis responds to HU-induced stress, we performed saturating transposon insertion mutagenesis followed by deep sequencing (Tn-seq), transcriptome sequencing (RNA-seq) analysis, and measurement of replication fork progression. Our data show that B. subtilis cells elongate, and replication fork progression is slowed, following HU challenge. The transcriptomic data show that B. subtilis cells initially mount a metabolic response likely caused by dNTP pool depletion before inducing the DNA damage response (SOS) after prolonged exposure. To compensate for reduced nucleotide pools, B. subtilis upregulates the purine and pyrimidine biosynthetic machinery and downregulates the enzymes producing ribose 5-phosphate. We show that overexpression of the RNR genes nrdEF suppresses the growth interference caused by HU, suggesting that RNR is an important target of HU in B. subtilis. Although genes involved in nucleotide and carbon metabolism showed considerable differential expression, we also find that genes of unknown function (y-genes) represent the largest class of differentially expressed genes. Deletion of individual y-genes caused moderate growth interference in the presence of HU, suggesting that cells have several ways of coping with HU-induced metabolic stress. IMPORTANCE Hydroxyurea (HU) has been widely used as a clinical therapeutic and an inhibitor of DNA replication. Some evidence suggests that HU inhibits ribonucleotide reductase, depleting dNTP pools, while other evidence shows that toxic HU breakdown products are responsible for growth inhibition and genotoxic stress. Here, we use multiple, complementary approaches to characterize the response of Bacillus subtilis to HU. B. subtilis responds by upregulating the expression of purine and pyrimidine biosynthesis. We show that HU challenge reduced DNA replication and that overexpression of the ribonucleotide reductase operon suppressed growth interference by HU. Our results demonstrate that HU targets RNR and several other metabolic enzymes contributing to toxicity in bacteria.
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Affiliation(s)
- Katherine J. Wozniak
- Department of Molecular, Cellular, and Developmental Biology, University of Michigan, Ann Arbor, Michigan, USA
| | - Lyle A. Simmons
- Department of Molecular, Cellular, and Developmental Biology, University of Michigan, Ann Arbor, Michigan, USA
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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.
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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
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Toyotake Y, Nishiyama M, Yokoyama F, Ogawa T, Kawamoto J, Kurihara T. A Novel Lysophosphatidic Acid Acyltransferase of Escherichia coli Produces Membrane Phospholipids with a cis-vaccenoyl Group and Is Related to Flagellar Formation. Biomolecules 2020; 10:E745. [PMID: 32403425 PMCID: PMC7277886 DOI: 10.3390/biom10050745] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2020] [Revised: 05/02/2020] [Accepted: 05/07/2020] [Indexed: 02/07/2023] Open
Abstract
Lysophosphatidic acid acyltransferase (LPAAT) introduces fatty acyl groups into the sn-2 position of membrane phospholipids (PLs). Various bacteria produce multiple LPAATs, whereas it is believed that Escherichia coli produces only one essential LPAAT homolog, PlsC-the deletion of which is lethal. However, we found that E. coli possesses another LPAAT homolog named YihG. Here, we show that overexpression of YihG in E. coli carrying a temperature-sensitive mutation in plsC allowed its growth at non-permissive temperatures. Analysis of the fatty acyl composition of PLs from the yihG-deletion mutant (∆yihG) revealed that endogenous YihG introduces the cis-vaccenoyl group into the sn-2 position of PLs. Loss of YihG did not affect cell growth or morphology, but ∆yihG cells swam well in liquid medium in contrast to wild-type cells. Immunoblot analysis showed that FliC was highly expressed in ∆yihG cells, and this phenotype was suppressed by expression of recombinant YihG in ∆yihG cells. Transmission electron microscopy confirmed that the flagellar structure was observed only in ∆yihG cells. These results suggest that YihG has specific functions related to flagellar formation through modulation of the fatty acyl composition of membrane PLs.
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Affiliation(s)
- Yosuke Toyotake
- Institute for Chemical Research, Kyoto University, Uji, Kyoto 611-0011, Japan; (Y.T.); (M.N.); (F.Y.); (T.O.); (J.K.)
- Department of Biotechnology, College of Life Sciences, Ritsumeikan University, 1-1-1 Noji-higashi, Kusatsu, Shiga 525-8577, Japan
| | - Masayoshi Nishiyama
- Institute for Chemical Research, Kyoto University, Uji, Kyoto 611-0011, Japan; (Y.T.); (M.N.); (F.Y.); (T.O.); (J.K.)
| | - Fumiaki Yokoyama
- Institute for Chemical Research, Kyoto University, Uji, Kyoto 611-0011, Japan; (Y.T.); (M.N.); (F.Y.); (T.O.); (J.K.)
| | - Takuya Ogawa
- Institute for Chemical Research, Kyoto University, Uji, Kyoto 611-0011, Japan; (Y.T.); (M.N.); (F.Y.); (T.O.); (J.K.)
| | - Jun Kawamoto
- Institute for Chemical Research, Kyoto University, Uji, Kyoto 611-0011, Japan; (Y.T.); (M.N.); (F.Y.); (T.O.); (J.K.)
| | - Tatsuo Kurihara
- Institute for Chemical Research, Kyoto University, Uji, Kyoto 611-0011, Japan; (Y.T.); (M.N.); (F.Y.); (T.O.); (J.K.)
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Grimwade JE, Rozgaja TA, Gupta R, Dyson K, Rao P, Leonard AC. Origin recognition is the predominant role for DnaA-ATP in initiation of chromosome replication. Nucleic Acids Res 2019; 46:6140-6151. [PMID: 29800247 PMCID: PMC6158602 DOI: 10.1093/nar/gky457] [Citation(s) in RCA: 22] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2017] [Accepted: 05/11/2018] [Indexed: 01/06/2023] Open
Abstract
In all cells, initiation of chromosome replication depends on the activity of AAA+ initiator proteins that form complexes with replication origin DNA. In bacteria, the conserved, adenosine triphosphate (ATP)-regulated initiator protein, DnaA, forms a complex with the origin, oriC, that mediates DNA strand separation and recruitment of replication machinery. Complex assembly and origin activation requires DnaA-ATP, which differs from DnaA-ADP in its ability to cooperatively bind specific low affinity sites and also to oligomerize into helical filaments. The degree to which each of these activities contributes to the DnaA-ATP requirement for initiation is not known. In this study, we compared the DnaA-ATP dependence of initiation from wild-type Escherichia coli oriC and a synthetic origin (oriCallADP), whose multiple low affinity DnaA sites bind DnaA-ATP and DnaA-ADP similarly. OriCallADP was fully occupied and unwound by DnaA-ADP in vitro, and, in vivo, oriCallADP suppressed lethality of DnaA mutants defective in ATP binding and ATP-specific oligomerization. However, loss of preferential DnaA-ATP binding caused over-initiation and increased sensitivity to replicative stress. The findings indicate both DnaA-ATP and DnaA-ADP can perform most of the mechanical functions needed for origin activation, and suggest that a key reason for ATP-regulation of DnaA is to control replication initiation frequency.
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Affiliation(s)
- Julia E Grimwade
- Department of Biological Sciences, Florida Institute of Technology, 150 W. University Blvd., Melbourne, FL 32901, USA
| | - Tania A Rozgaja
- AREVA Inc North America, 6100 Southwest Blvd #400, Benbrook, TX 76109, USA
| | - Rajat Gupta
- Department of Biological Sciences, Florida Institute of Technology, 150 W. University Blvd., Melbourne, FL 32901, USA
| | - Kyle Dyson
- University of Florida College of Medicine, P.O. Box 100215, Gainesville, FL 32610, USA
| | - Prassanna Rao
- Department of Biological Sciences, Florida Institute of Technology, 150 W. University Blvd., Melbourne, FL 32901, USA
| | - Alan C Leonard
- Department of Biological Sciences, Florida Institute of Technology, 150 W. University Blvd., Melbourne, FL 32901, USA
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Reyes-Lamothe R, Sherratt DJ. The bacterial cell cycle, chromosome inheritance and cell growth. Nat Rev Microbiol 2019; 17:467-478. [DOI: 10.1038/s41579-019-0212-7] [Citation(s) in RCA: 43] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
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Coping with Reactive Oxygen Species to Ensure Genome Stability in Escherichia coli. Genes (Basel) 2018; 9:genes9110565. [PMID: 30469410 PMCID: PMC6267047 DOI: 10.3390/genes9110565] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2018] [Revised: 11/15/2018] [Accepted: 11/16/2018] [Indexed: 12/16/2022] Open
Abstract
The facultative aerobic bacterium Escherichia coli adjusts its cell cycle to environmental conditions. Because of its lifestyle, the bacterium has to balance the use of oxygen with the potential lethal effects of its poisonous derivatives. Oxidative damages perpetrated by molecules such as hydrogen peroxide and superoxide anions directly incapacitate metabolic activities relying on enzymes co-factored with iron and flavins. Consequently, growth is inhibited when the bacterium faces substantial reactive oxygen insults coming from environmental or cellular sources. Although hydrogen peroxide and superoxide anions do not oxidize DNA directly, these molecules feed directly or indirectly the generation of the highly reactive hydroxyl radical that damages the bacterial chromosome. Oxidized bases are normally excised and the single strand gap repaired by the base excision repair pathway (BER). This process is especially problematic in E. coli because replication forks do not sense the presence of damages or a stalled fork ahead of them. As consequence, single-strand breaks are turned into double-strand breaks (DSB) through replication. Since E. coli tolerates the presence of DSBs poorly, BER can become toxic during oxidative stress. Here we review the repair strategies that E. coli adopts to preserve genome integrity during oxidative stress and their relation to cell cycle control of DNA replication.
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Origins Left, Right, and Centre: Increasing the Number of Initiation Sites in the Escherichia coli Chromosome. Genes (Basel) 2018; 9:genes9080376. [PMID: 30060465 PMCID: PMC6116050 DOI: 10.3390/genes9080376] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2018] [Revised: 07/20/2018] [Accepted: 07/23/2018] [Indexed: 11/17/2022] Open
Abstract
The bacterium Escherichia coli contains a single circular chromosome with a defined architecture. DNA replication initiates at a single origin called oriC. Two replication forks are assembled and proceed in opposite directions until they fuse in a specialised zone opposite the origin. This termination area is flanked by polar replication fork pause sites that allow forks to enter, but not to leave. Thus, the chromosome is divided into two replichores, each replicated by a single replication fork. Recently, we analysed the replication parameters in E. coli cells, in which an ectopic origin termed oriZ was integrated in the right-hand replichore. Two major obstacles to replication were identified: (1) head-on replication⁻transcription conflicts at highly transcribed rrn operons, and (2) the replication fork trap. Here, we describe replication parameters in cells with ectopic origins, termed oriX and oriY, integrated into the left-hand replichore, and a triple origin construct with oriX integrated in the left-hand and oriZ in the right-hand replichore. Our data again highlight both replication⁻transcription conflicts and the replication fork trap as important obstacles to DNA replication, and we describe a number of spontaneous large genomic rearrangements which successfully alleviate some of the problems arising from having an additional origin in an ectopic location. However, our data reveal additional factors that impact efficient chromosome duplication, highlighting the complexity of chromosomal architecture.
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Iron chelation increases the tolerance of Escherichia coli to hyper-replication stress. Sci Rep 2018; 8:10550. [PMID: 30002429 PMCID: PMC6043582 DOI: 10.1038/s41598-018-28841-9] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2018] [Accepted: 06/29/2018] [Indexed: 11/08/2022] Open
Abstract
In Escherichia coli, an increase in the frequency of chromosome replication is lethal. In order to identify compounds that affect chromosome replication, we screened for molecules capable of restoring the viability of hyper-replicating cells. We made use of two E. coli strains that over-initiate DNA replication by keeping the DnaA initiator protein in its active ATP bound state. While viable under anaerobic growth or when grown on poor media, these strains become inviable when grown in rich media. Extracts from actinomycetes strains were screened, leading to the identification of deferoxamine (DFO) as the active compound in one of them. We show that DFO does not affect chromosomal replication initiation and suggest that it was identified due to its ability to chelate cellular iron. This limits the formation of reactive oxygen species, reduce oxidative DNA damage and promote processivity of DNA replication. We argue that the benzazepine derivate (±)-6-Chloro-PB hydrobromide acts in a similar manner.
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Charbon G, Riber L, Løbner-Olesen A. Countermeasures to survive excessive chromosome replication in Escherichia coli. Curr Genet 2017; 64:71-79. [PMID: 28664289 DOI: 10.1007/s00294-017-0725-4] [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: 06/15/2017] [Revised: 06/20/2017] [Accepted: 06/22/2017] [Indexed: 02/05/2023]
Abstract
In Escherichia coli, like all organisms, DNA replication is coordinated with cell cycle progression to ensure duplication of the genome prior to cell division. Chromosome replication is initiated from the replication origin, oriC, by the DnaA protein associated with ATP. Initiations take place once per cell cycle and in synchrony at all cellular origins. DnaA also binds ADP with similar affinity as ATP and in wild-type cells the majority of DnaA molecules are ADP bound. In cells where the DnaAATP/DnaAADP ratio increases or in cells where DnaAATP has increased access to oriC, premature initiations take place, often referred to as overinitiation. Overinitiating cells are generally characterized by their slow growth and in the most severe cases lethal accumulation of DNA strand breaks. Here, we review the different strategies adopted by E. coli to survive overinitiation. We propose a unifying model where all mutations that suppress overinitiation keep replication forks separated in time and, thereby, reduce the formation of strand breaks. One group of mutations does so by lowering the activity of oriC and/or DnaA to reduce the frequency of initiations to an acceptable level. In the other group of mutations, replication forks are kept apart by preventing formation of damages that would otherwise cause replication blocks, by allowing bypass of replication blocks and/or by slowing down replication forks. This group of suppressors restores viability despite excessive chromosome replication and provides new insights into mechanisms that safeguard DNA integrity.
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Affiliation(s)
- Godefroid Charbon
- Department of Biology, University of Copenhagen, Ole Maaløes Vej 5, 2200, Copenhagen N, Denmark.
| | - Leise Riber
- Department of Biology, University of Copenhagen, Ole Maaløes Vej 5, 2200, Copenhagen N, Denmark
| | - Anders Løbner-Olesen
- Department of Biology, University of Copenhagen, Ole Maaløes Vej 5, 2200, Copenhagen N, Denmark.
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