1
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Vilar JMG, Saiz L. The unreasonable effectiveness of equilibrium gene regulation through the cell cycle. Cell Syst 2024; 15:639-648.e2. [PMID: 38981487 DOI: 10.1016/j.cels.2024.06.002] [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: 10/06/2022] [Revised: 06/19/2023] [Accepted: 06/14/2024] [Indexed: 07/11/2024]
Abstract
Systems like the prototypical lac operon can reliably hold repression of transcription upon DNA replication across cell cycles with just 10 repressor molecules per cell and behave as if they were at equilibrium. The origin of this phenomenology is still an unresolved question. Here, we develop a general theory to analyze strong perturbations in quasi-equilibrium systems and use it to quantify the effects of DNA replication in gene regulation. We find a scaling law linking actual with predicted equilibrium transcription via a single kinetic parameter. We show that even the lac operon functions beyond the physical limits of naive regulation through compensatory mechanisms that suppress non-equilibrium effects. Synthetic systems without adjuvant activators, such as the cAMP receptor protein (CRP), lack this reliability. Our results provide a rationale for the function of CRP, beyond just being a tunable activator, as a mitigator of cell cycle perturbations.
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Affiliation(s)
- Jose M G Vilar
- Biofisika Institute (CSIC, UPV/EHU), University of the Basque Country (UPV/EHU), P.O. Box 644, 48080 Bilbao, Spain; IKERBASQUE, Basque Foundation for Science, 48011 Bilbao, Spain.
| | - Leonor Saiz
- Department of Biomedical Engineering, University of California, 451 E. Health Sciences Drive, Davis, CA 95616, USA; Max Planck Institute for the Physics of Complex Systems, 01187 Dresden, Germany; Center for Systems Biology Dresden, 01307 Dresden, Germany.
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2
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Pountain AW, Jiang P, Yao T, Homaee E, Guan Y, McDonald KJC, Podkowik M, Shopsin B, Torres VJ, Golding I, Yanai I. Transcription-replication interactions reveal bacterial genome regulation. Nature 2024; 626:661-669. [PMID: 38267581 PMCID: PMC10923101 DOI: 10.1038/s41586-023-06974-w] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2023] [Accepted: 12/14/2023] [Indexed: 01/26/2024]
Abstract
Organisms determine the transcription rates of thousands of genes through a few modes of regulation that recur across the genome1. In bacteria, the relationship between the regulatory architecture of a gene and its expression is well understood for individual model gene circuits2,3. However, a broader perspective of these dynamics at the genome scale is lacking, in part because bacterial transcriptomics has hitherto captured only a static snapshot of expression averaged across millions of cells4. As a result, the full diversity of gene expression dynamics and their relation to regulatory architecture remains unknown. Here we present a novel genome-wide classification of regulatory modes based on the transcriptional response of each gene to its own replication, which we term the transcription-replication interaction profile (TRIP). Analysing single-bacterium RNA-sequencing data, we found that the response to the universal perturbation of chromosomal replication integrates biological regulatory factors with biophysical molecular events on the chromosome to reveal the local regulatory context of a gene. Whereas the TRIPs of many genes conform to a gene dosage-dependent pattern, others diverge in distinct ways, and this is shaped by factors such as intra-operon position and repression state. By revealing the underlying mechanistic drivers of gene expression heterogeneity, this work provides a quantitative, biophysical framework for modelling replication-dependent expression dynamics.
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Affiliation(s)
- Andrew W Pountain
- Institute for Systems Genetics, NYU Grossman School of Medicine, New York, NY, USA
| | - Peien Jiang
- Institute for Systems Genetics, NYU Grossman School of Medicine, New York, NY, USA
- Department of Biology, New York University, New York, NY, USA
| | - Tianyou Yao
- Department of Physics, University of Illinois at Urbana Champaign, Urbana, IL, USA
| | - Ehsan Homaee
- Department of Physics, University of Illinois at Urbana Champaign, Urbana, IL, USA
- Center for Biophysics and Computational Biology, University of Illinois at Urbana-Champaign, Urbana, IL, USA
| | - Yichao Guan
- Department of Physics, University of Illinois at Urbana Champaign, Urbana, IL, USA
| | - Kevin J C McDonald
- Department of Physics, University of Illinois at Urbana Champaign, Urbana, IL, USA
| | - Magdalena Podkowik
- Department of Medicine, Division of Infectious Diseases, NYU Grossman School of Medicine, New York, NY, USA
| | - Bo Shopsin
- Department of Medicine, Division of Infectious Diseases, NYU Grossman School of Medicine, New York, NY, USA
- Department of Microbiology, NYU Grossman School of Medicine, New York, NY, USA
| | - Victor J Torres
- Department of Microbiology, NYU Grossman School of Medicine, New York, NY, USA
- Department of Host-Microbe Interactions, St. Jude Children's Research Hospital, Memphis, TN, USA
| | - Ido Golding
- Department of Physics, University of Illinois at Urbana Champaign, Urbana, IL, USA
- Department of Microbiology, University of Illinois at Urbana-Champaign, Urbana, IL, USA
| | - Itai Yanai
- Institute for Systems Genetics, NYU Grossman School of Medicine, New York, NY, USA.
- Department of Biochemistry and Molecular Pharmacology, NYU Grossman School of Medicine, New York, NY, USA.
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3
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Fu H, Xiao F, Jun S. Bacterial Replication Initiation as Precision Control by Protein Counting. PRX LIFE 2023; 1:013011. [PMID: 38550259 PMCID: PMC10977104 DOI: 10.1103/prxlife.1.013011] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Indexed: 04/09/2024]
Abstract
Balanced biosynthesis is the hallmark of bacterial cell physiology, where the concentrations of stable proteins remain steady. However, this poses a conceptual challenge to modeling the cell-cycle and cell-size controls in bacteria, as prevailing concentration-based eukaryote models are not directly applicable. In this study, we revisit and significantly extend the initiator-titration model, proposed 30 years ago, and we explain how bacteria precisely and robustly control replication initiation based on the mechanism of protein copy-number sensing. Using a mean-field approach, we first derive an analytical expression of the cell size at initiation based on three biological mechanistic control parameters for an extended initiator-titration model. We also study the stability of our model analytically and show that initiation can become unstable in multifork replication conditions. Using simulations, we further show that the presence of the conversion between active and inactive initiator protein forms significantly represses initiation instability. Importantly, the two-step Poisson process set by the initiator titration step results in significantly improved initiation synchrony with C V ~ 1 / N scaling rather than the standard 1 / N scaling in the Poisson process, where N is the total number of initiators required for initiation. Our results answer two long-standing questions in replication initiation: (i) Why do bacteria produce almost two orders of magnitude more DnaA, the master initiator proteins, than required for initiation? (ii) Why does DnaA exist in active (DnaA-ATP) and inactive (DnaA-ADP) forms if only the active form is competent for initiation? The mechanism presented in this work provides a satisfying general solution to how the cell can achieve precision control without sensing protein concentrations, with broad implications from evolution to the design of synthetic cells.
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Affiliation(s)
- Haochen Fu
- Department of Physics, University of California San Diego, 9500 Gilman Drive, La Jolla, California 92093, USA
| | - Fangzhou Xiao
- Department of Physics, University of California San Diego, 9500 Gilman Drive, La Jolla, California 92093, USA
| | - Suckjoon Jun
- Department of Physics and Department of Molecular Biology, University of California San Diego, 9500 Gilman Drive, La Jolla, California 92093, USA
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4
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Goodall DJ, Warecka D, Hawkins M, Rudolph CJ. Interplay between chromosomal architecture and termination of DNA replication in bacteria. Front Microbiol 2023; 14:1180848. [PMID: 37434703 PMCID: PMC10331603 DOI: 10.3389/fmicb.2023.1180848] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2023] [Accepted: 06/05/2023] [Indexed: 07/13/2023] Open
Abstract
Faithful transmission of the genome from one generation to the next is key to life in all cellular organisms. In the majority of bacteria, the genome is comprised of a single circular chromosome that is normally replicated from a single origin, though additional genetic information may be encoded within much smaller extrachromosomal elements called plasmids. By contrast, the genome of a eukaryote is distributed across multiple linear chromosomes, each of which is replicated from multiple origins. The genomes of archaeal species are circular, but are predominantly replicated from multiple origins. In all three cases, replication is bidirectional and terminates when converging replication fork complexes merge and 'fuse' as replication of the chromosomal DNA is completed. While the mechanics of replication initiation are quite well understood, exactly what happens during termination is far from clear, although studies in bacterial and eukaryotic models over recent years have started to provide some insight. Bacterial models with a circular chromosome and a single bidirectional origin offer the distinct advantage that there is normally just one fusion event between two replication fork complexes as synthesis terminates. Moreover, whereas termination of replication appears to happen in many bacteria wherever forks happen to meet, termination in some bacterial species, including the well-studied bacteria Escherichia coli and Bacillus subtilis, is more restrictive and confined to a 'replication fork trap' region, making termination even more tractable. This region is defined by multiple genomic terminator (ter) sites, which, if bound by specific terminator proteins, form unidirectional fork barriers. In this review we discuss a range of experimental results highlighting how the fork fusion process can trigger significant pathologies that interfere with the successful conclusion of DNA replication, how these pathologies might be resolved in bacteria without a fork trap system and how the acquisition of a fork trap might have provided an alternative and cleaner solution, thus explaining why in bacterial species that have acquired a fork trap system, this system is remarkably well maintained. Finally, we consider how eukaryotic cells can cope with a much-increased number of termination events.
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Affiliation(s)
- Daniel J. Goodall
- Division of Biosciences, College of Health, Medicine and Life Sciences, Brunel University London, Uxbridge, United Kingdom
| | | | | | - Christian J. Rudolph
- Division of Biosciences, College of Health, Medicine and Life Sciences, Brunel University London, Uxbridge, United Kingdom
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5
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Ashour ME, Byrum AK, Meroni A, Xia J, Singh S, Galletto R, Rosenberg SM, Vindigni A, Mosammaparast N. Rapid profiling of DNA replication dynamics using mass spectrometry-based analysis of nascent DNA. J Cell Biol 2023; 222:e202207121. [PMID: 36795402 PMCID: PMC9960042 DOI: 10.1083/jcb.202207121] [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: 07/26/2022] [Revised: 12/09/2022] [Accepted: 01/19/2023] [Indexed: 02/17/2023] Open
Abstract
The primary method for probing DNA replication dynamics is DNA fiber analysis, which utilizes thymidine analog incorporation into nascent DNA, followed by immunofluorescent microscopy of DNA fibers. Besides being time-consuming and prone to experimenter bias, it is not suitable for studying DNA replication dynamics in mitochondria or bacteria, nor is it adaptable for higher-throughput analysis. Here, we present mass spectrometry-based analysis of nascent DNA (MS-BAND) as a rapid, unbiased, quantitative alternative to DNA fiber analysis. In this method, incorporation of thymidine analogs is quantified from DNA using triple quadrupole tandem mass spectrometry. MS-BAND accurately detects DNA replication alterations in both the nucleus and mitochondria of human cells, as well as bacteria. The high-throughput capability of MS-BAND captured replication alterations in an E. coli DNA damage-inducing gene library. Therefore, MS-BAND may serve as an alternative to the DNA fiber technique, with potential for high-throughput analysis of replication dynamics in diverse model systems.
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Affiliation(s)
- Mohamed E. Ashour
- Department of Pathology and Immunology, Washington University in St. Louis School of Medicine, St. Louis, MO, USA
| | - Andrea K. Byrum
- Department of Pathology and Immunology, Washington University in St. Louis School of Medicine, St. Louis, MO, USA
- Center for Childhood Cancer & Blood Diseases, Nationwide Children’s Hospital, Columbus, OH, USA
| | - Alice Meroni
- Division of Oncology, Department of Medicine, Washington University in St. Louis School of Medicine, St. Louis, MO, USA
| | - Jun Xia
- Departments of Molecular and Human Genetics, Biochemistry and Molecular Biology, and Molecular Virology and Microbiology, Baylor College of Medicine, Houston, TX, USA
- Department of Biomedical Sciences, Creighton University, Omaha, NE, USA
| | - Saurabh Singh
- Department of Biochemistry and Molecular Biophysics, Washington University in St. Louis School of Medicine, St. Louis, MO, USA
| | - Roberto Galletto
- Department of Biochemistry and Molecular Biophysics, Washington University in St. Louis School of Medicine, St. Louis, MO, USA
| | - Susan M. Rosenberg
- Departments of Molecular and Human Genetics, Biochemistry and Molecular Biology, and Molecular Virology and Microbiology, Baylor College of Medicine, Houston, TX, USA
| | - Alessandro Vindigni
- Division of Oncology, Department of Medicine, Washington University in St. Louis School of Medicine, St. Louis, MO, USA
| | - Nima Mosammaparast
- Department of Pathology and Immunology, Washington University in St. Louis School of Medicine, St. Louis, MO, USA
- Division of Oncology, Department of Medicine, Washington University in St. Louis School of Medicine, St. Louis, MO, USA
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6
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Sanders S, Joshi K, Levin PA, Iyer-Biswas S. Beyond the average: An updated framework for understanding the relationship between cell growth, DNA replication, and division in a bacterial system. PLoS Genet 2023; 19:e1010505. [PMID: 36602967 DOI: 10.1371/journal.pgen.1010505] [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] [Indexed: 01/06/2023] Open
Abstract
Our understanding of the bacterial cell cycle is framed largely by population-based experiments that focus on the behavior of idealized average cells. Most famously, the contributions of Cooper and Helmstetter help to contextualize the phenomenon of overlapping replication cycles observed in rapidly growing bacteria. Despite the undeniable value of these approaches, their necessary reliance on the behavior of idealized average cells masks the stochasticity inherent in single-cell growth and physiology and limits their mechanistic value. To bridge this gap, we propose an updated and agnostic framework, informed by extant single-cell data, that quantitatively accounts for stochastic variations in single-cell dynamics and the impact of medium composition on cell growth and cell cycle progression. In this framework, stochastic timers sensitive to medium composition impact the relationship between cell cycle events, accounting for observed differences in the relationship between cell cycle events in slow- and fast-growing cells. We conclude with a roadmap for potential application of this framework to longstanding open questions in the bacterial cell cycle field.
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Affiliation(s)
- Sara Sanders
- Department of Biology, Washington University in St. Louis, St. Louis, Missouri, United States of America
| | - Kunaal Joshi
- Department of Physics and Astronomy, Purdue University, West Lafayette, Indiana, United States of America
| | - Petra Anne Levin
- Department of Biology, Washington University in St. Louis, St. Louis, Missouri, United States of America
| | - Srividya Iyer-Biswas
- Department of Physics and Astronomy, Purdue University, West Lafayette, Indiana, United States of America
- Santa Fe Institute, Santa Fe, New Mexico, United States of America
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7
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Bhat D, Hauf S, Plessy C, Yokobayashi Y, Pigolotti S. Speed variations of bacterial replisomes. eLife 2022; 11:75884. [PMID: 35877175 PMCID: PMC9385209 DOI: 10.7554/elife.75884] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2021] [Accepted: 07/13/2022] [Indexed: 11/13/2022] Open
Abstract
Replisomes are multi-protein complexes that replicate genomes with remarkable speed and accuracy. Despite their importance, their dynamics is poorly characterized, especially in vivo. In this paper, we present an approach to infer the replisome dynamics from the DNA abundance distribution measured in a growing bacterial population. Our method is sensitive enough to detect subtle variations of the replisome speed along the genome. As an application, we experimentally measured the DNA abundance distribution in Escherichia coli populations growing at different temperatures using deep sequencing. We find that the average replisome speed increases nearly five-fold between 17°C and 37°C. Further, we observe wave-like variations of the replisome speed along the genome. These variations correlate with previously observed variations of the mutation rate, suggesting a common dynamical origin. Our approach has the potential to elucidate replication dynamics in E. coli mutants and in other bacterial species.
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Affiliation(s)
- Deepak Bhat
- Biological Complexity Unit, Okinawa Institute of Science and Technology, Onna, Japan
| | - Samuel Hauf
- Nucleic Acid Chemistry and Engineering Unit, Okinawa Institute of Science and Technology, Onna, Japan
| | - Charles Plessy
- Genomics and Regulatory Systems Unit, Okinawa Institute of Science and Technology, Onna, Japan
| | - Yohei Yokobayashi
- Nucleic Acid Chemistry and Engineering Unit, Okinawa Institute of Science and Technology, Onna, Japan
| | - Simone Pigolotti
- Biological Complexity Unit, Okinawa Institute of Science and Technology, Onna, Japan
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8
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Wang X, Zheng W, Zhou H, Tu Q, Tang YJ, Stewart AF, Zhang Y, Bian X. Improved dsDNA recombineering enables versatile multiplex genome engineering of kilobase-scale sequences in diverse bacteria. Nucleic Acids Res 2021; 50:e15. [PMID: 34792175 PMCID: PMC8860599 DOI: 10.1093/nar/gkab1076] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2021] [Revised: 09/23/2021] [Accepted: 10/22/2021] [Indexed: 01/21/2023] Open
Abstract
Recombineering assisted multiplex genome editing generally uses single-stranded oligonucleotides for site directed mutational changes. It has proven highly efficient for functional screens and to optimize microbial cell factories. However, this approach is limited to relatively small mutational changes. Here, we addressed the challenges involved in the use of double-stranded DNA substrates for multiplex genome engineering. Recombineering is mediated by phage single-strand annealing proteins annealing ssDNAs into the replication fork. We apply this insight to facilitate the generation of ssDNA from the dsDNA substrate and to alter the speed of replication by elevating the available deoxynucleoside triphosphate (dNTP) levels. Intracellular dNTP concentration was elevated by ribonucleotide reductase overexpression or dNTP addition to establish double-stranded DNA Recombineering-assisted Multiplex Genome Engineering (dReaMGE), which enables rapid and flexible insertional and deletional mutagenesis at multiple sites on kilobase scales in diverse bacteria without the generation of double-strand breaks or disturbance of the mismatch repair system. dReaMGE can achieve combinatorial genome engineering works, for example, alterations to multiple biosynthetic pathways, multiple promoter or gene insertions, variations of transcriptional regulator combinations, within a few days. dReaMGE adds to the repertoire of bacterial genome engineering to facilitate discovery, functional genomics, strain optimization and directed evolution of microbial cell factories.
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Affiliation(s)
- Xue Wang
- Helmholtz International Lab for Anti-Infectives, Shandong University-Helmholtz Institute of Biotechnology, State Key Laboratory of Microbial Technology, Shandong University, Qingdao, Shandong 266237, China
| | - Wentao Zheng
- Helmholtz International Lab for Anti-Infectives, Shandong University-Helmholtz Institute of Biotechnology, State Key Laboratory of Microbial Technology, Shandong University, Qingdao, Shandong 266237, China
| | - Haibo Zhou
- Helmholtz International Lab for Anti-Infectives, Shandong University-Helmholtz Institute of Biotechnology, State Key Laboratory of Microbial Technology, Shandong University, Qingdao, Shandong 266237, China
| | - Qiang Tu
- Helmholtz International Lab for Anti-Infectives, Shandong University-Helmholtz Institute of Biotechnology, State Key Laboratory of Microbial Technology, Shandong University, Qingdao, Shandong 266237, China
| | - Ya-Jie Tang
- Helmholtz International Lab for Anti-Infectives, Shandong University-Helmholtz Institute of Biotechnology, State Key Laboratory of Microbial Technology, Shandong University, Qingdao, Shandong 266237, China
| | - A Francis Stewart
- Genomics, Biotechnology Center, Center for Molecular and Cellular Bioengineering, Technische Universität Dresden, Tatzberg 47-51, 01307 Dresden, Germany
| | - Youming Zhang
- Helmholtz International Lab for Anti-Infectives, Shandong University-Helmholtz Institute of Biotechnology, State Key Laboratory of Microbial Technology, Shandong University, Qingdao, Shandong 266237, China
| | - Xiaoying Bian
- Helmholtz International Lab for Anti-Infectives, Shandong University-Helmholtz Institute of Biotechnology, State Key Laboratory of Microbial Technology, Shandong University, Qingdao, Shandong 266237, China
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9
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Jameson KH, Rudolph CJ, Hawkins M. Termination of DNA replication at Tus-ter barriers results in under-replication of template DNA. J Biol Chem 2021; 297:101409. [PMID: 34780717 DOI: 10.1016/j.jbc.2021.101409] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/24/2021] [Revised: 11/02/2021] [Accepted: 11/10/2021] [Indexed: 02/05/2023] Open
Abstract
The complete and accurate duplication of genomic information is vital to maintain genome stability in all domains of life. In Escherichia coli, replication termination, the final stage of the duplication process, is confined to the 'replication fork trap' region by multiple unidirectional fork barriers formed by the binding of Tus protein to genomic ter sites. Termination typically occurs away from Tus-ter complexes, but they become part of the fork fusion process when a delay to one replisome allows the second replisome to travel more than halfway around the chromosome. In this instance, replisome progression is blocked at the non-permissive interface of the Tus-ter complex, termination then occurs when a converging replisome meets the permissive interface. To investigate the consequences of replication fork fusion at Tus-ter complexes, we established a plasmid-based replication system where we could mimic the termination process at Tus-ter complexes in vitro. We developed a termination mapping assay to measure leading strand replication fork progression and demonstrate that the DNA template is under-replicated by 15-24 bases when replication forks fuse at Tus-ter complexes. This gap could not be closed by the addition of lagging strand processing enzymes or by the inclusion of several helicases that promote DNA replication. Our results indicate that accurate fork fusion at Tus-ter barriers requires further enzymatic processing, highlighting large gaps that still exist in our understanding of the final stages of chromosome duplication and the evolutionary advantage of having a replication fork trap.
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Affiliation(s)
- Katie H Jameson
- Department of Biology, University of York, Wentworth Way, York, YO10 5DD, UK
| | - Christian J Rudolph
- Division of Biosciences, College of Health, Medicine and Life Sciences, Brunel University London, Uxbridge, UB8 3PH, UK
| | - Michelle Hawkins
- Department of Biology, University of York, Wentworth Way, York, YO10 5DD, UK.
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10
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DNA Replication-Transcription Conflicts Do Not Significantly Contribute to Spontaneous Mutations Due to Replication Errors in Escherichia coli. mBio 2021; 12:e0250321. [PMID: 34634932 PMCID: PMC8510543 DOI: 10.1128/mbio.02503-21] [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] [Indexed: 01/18/2023] Open
Abstract
Encounters between DNA replication and transcription can cause genomic disruption, particularly when the two meet head-on. Whether these conflicts produce point mutations is debated. This paper presents detailed analyses of a large collection of mutations generated during mutation accumulation experiments with mismatch repair (MMR)-defective Escherichia coli. With MMR absent, mutations are primarily due to DNA replication errors. Overall, there were no differences in the frequencies of base pair substitutions or small indels (i.e., insertion and deletions of ≤4 bp) in the coding sequences or promoters of genes oriented codirectionally versus head-on to replication. Among a subset of highly expressed genes, there was a 2- to 3-fold bias for indels in genes oriented head-on to replication, but this difference was almost entirely due to the asymmetrical genomic locations of tRNA genes containing mononucleotide runs, which are hot spots for indels. No additional orientation bias in mutation frequencies occurred when MMR− strains were also defective for transcription-coupled repair (TCR). However, in contrast to other reports, loss of TCR slightly increased the overall mutation rate, meaning that TCR is antimutagenic. There was no orientation bias in mutation frequencies among the stress response genes that are regulated by RpoS or induced by DNA damage. Thus, biases in the locations of mutational targets can account for most, if not all, apparent biases in mutation frequencies between genes oriented head-on versus codirectional to replication. In addition, the data revealed a strong correlation of the frequency of base pair substitutions with gene length but no correlation with gene expression levels.
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11
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Hu B, Wang Y, Sun S, Luo G, Zhang S, Zhang J, Chen L, Huang Z. Specificity Enhancement of Deoxyribonucleic Acid Polymerization for Sensitive Nucleic Acid Detection. Anal Chem 2020; 92:15872-15879. [PMID: 33236629 DOI: 10.1021/acs.analchem.0c03223] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
Specificity of DNA polymerization plays a critical role in DNA replication and storage of genetic information. Likewise, biotechnological applications, such as nucleic acid detection, DNA amplification, and gene cloning, require high specificity in DNA synthesis catalyzed by DNA polymerases. However, errors in DNA polymerization (such as mis-incorporation and mis-priming) can significantly jeopardize the specificity. Herein, we report our discovery that the specificity of DNA enzymatic synthesis can be substantially enhanced (up to 100-fold higher) by attenuating DNA polymerase kinetics via the phosphorothioate dNTPs. This specificity enhancement allows convenient and sensitive nucleic acid detection, polymerization, PCR, and gene cloning with complex systems (such as human cDNA and genomic DNA). Further, we found that the specificity enhancement offered higher sensitivity (up to 50-fold better) for detecting nucleic acids, such as COVID-19 viral RNAs. Our findings have revealed a simple and convenient strategy for facilitating specificity and sensitivity of nucleic acid detection, amplification, and gene cloning.
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Affiliation(s)
- Bei Hu
- Key Laboratory of Bio-Resource and Eco-environment of Ministry of Education, College of Life Sciences, Sichuan University, Chengdu 610064, Sichuan, P. R. China
| | - Yitao Wang
- Key Laboratory of Bio-Resource and Eco-environment of Ministry of Education, College of Life Sciences, Sichuan University, Chengdu 610064, Sichuan, P. R. China
| | - Shichao Sun
- Key Laboratory of Bio-Resource and Eco-environment of Ministry of Education, College of Life Sciences, Sichuan University, Chengdu 610064, Sichuan, P. R. China
| | - Guangcheng Luo
- Key Laboratory of Bio-Resource and Eco-environment of Ministry of Education, College of Life Sciences, Sichuan University, Chengdu 610064, Sichuan, P. R. China
| | - Shun Zhang
- Key Laboratory of Bio-Resource and Eco-environment of Ministry of Education, College of Life Sciences, Sichuan University, Chengdu 610064, Sichuan, P. R. China
| | - Jun Zhang
- Key Laboratory of Bio-Resource and Eco-environment of Ministry of Education, College of Life Sciences, Sichuan University, Chengdu 610064, Sichuan, P. R. China
| | - Lu Chen
- Szostak-CDHT Institute for Large Nucleic Acids, Chengdu 610041, Sichuan, P.R. China
| | - Zhen Huang
- Key Laboratory of Bio-Resource and Eco-environment of Ministry of Education, College of Life Sciences, Sichuan University, Chengdu 610064, Sichuan, P. R. China.,Szostak-CDHT Institute for Large Nucleic Acids, Chengdu 610041, Sichuan, P.R. China
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12
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Crucial Role of the C-Terminal Domain of Hfq Protein in Genomic Instability. Microorganisms 2020; 8:microorganisms8101598. [PMID: 33080799 PMCID: PMC7603069 DOI: 10.3390/microorganisms8101598] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2020] [Revised: 10/10/2020] [Accepted: 10/13/2020] [Indexed: 01/25/2023] Open
Abstract
G-rich DNA repeats that can form G-quadruplex structures are prevalent in bacterial genomes and are frequently associated with regulatory regions of genes involved in virulence, antigenic variation, and antibiotic resistance. These sequences are also inherently mutagenic and can lead to changes affecting cell survival and adaptation. Transcription of the G-quadruplex-forming repeat (G3T)n in E. coli, when mRNA comprised the G-rich strand, promotes G-quadruplex formation in DNA and increases rates of deletion of G-quadruplex-forming sequences. The genomic instability of G-quadruplex repeats may be a source of genetic variability that can influence alterations and evolution of bacteria. The DNA chaperone Hfq is involved in the genetic instability of these G-quadruplex sequences. Inactivation of the hfq gene decreases the genetic instability of G-quadruplex, demonstrating that the genomic instability of this regulatory element can be influenced by the E. coli highly pleiotropic Hfq protein, which is involved in small noncoding RNA regulation pathways, and DNA organization and packaging. We have shown previously that the protein binds to and stabilizes these sequences, increasing rates of their genomic instability. Here, we extend this analysis to characterize the role of the C-terminal domain of Hfq protein in interaction with G-quadruplex structures. This allows to better understand the function of this specific region of the Hfq protein in genomic instability.
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Joseph AM, Badrinarayanan A. Visualizing mutagenic repair: novel insights into bacterial translesion synthesis. FEMS Microbiol Rev 2020; 44:572-582. [PMID: 32556198 PMCID: PMC7476773 DOI: 10.1093/femsre/fuaa023] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2019] [Accepted: 06/17/2020] [Indexed: 12/15/2022] Open
Abstract
DNA repair is essential for cell survival. In all domains of life, error-prone and error-free repair pathways ensure maintenance of genome integrity under stress. Mutagenic, low-fidelity repair mechanisms help avoid potential lethality associated with unrepaired damage, thus making them important for genome maintenance and, in some cases, the preferred mode of repair. However, cells carefully regulate pathway choice to restrict activity of these pathways to only certain conditions. One such repair mechanism is translesion synthesis (TLS), where a low-fidelity DNA polymerase is employed to synthesize across a lesion. In bacteria, TLS is a potent source of stress-induced mutagenesis, with potential implications in cellular adaptation as well as antibiotic resistance. Extensive genetic and biochemical studies, predominantly in Escherichia coli, have established a central role for TLS in bypassing bulky DNA lesions associated with ongoing replication, either at or behind the replication fork. More recently, imaging-based approaches have been applied to understand the molecular mechanisms of TLS and how its function is regulated. Together, these studies have highlighted replication-independent roles for TLS as well. In this review, we discuss the current status of research on bacterial TLS, with emphasis on recent insights gained mostly through microscopy at the single-cell and single-molecule level.
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Affiliation(s)
- Asha Mary Joseph
- National Centre for Biological Sciences (Tata Institute of Fundamental Research), Bangalore, Karnataka 560065, India
| | - Anjana Badrinarayanan
- National Centre for Biological Sciences (Tata Institute of Fundamental Research), Bangalore, Karnataka 560065, India
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14
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Syeda AH, Dimude JU, Skovgaard O, Rudolph CJ. Too Much of a Good Thing: How Ectopic DNA Replication Affects Bacterial Replication Dynamics. Front Microbiol 2020; 11:534. [PMID: 32351461 PMCID: PMC7174701 DOI: 10.3389/fmicb.2020.00534] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2020] [Accepted: 03/12/2020] [Indexed: 12/15/2022] Open
Abstract
Each cell division requires the complete and accurate duplication of the entire genome. In bacteria, the duplication process of the often-circular chromosomes is initiated at a single origin per chromosome, resulting in two replication forks that traverse the chromosome in opposite directions. DNA synthesis is completed once the two forks fuse in a region diametrically opposite the origin. In some bacteria, such as Escherichia coli, the region where forks fuse forms a specialized termination area. Polar replication fork pause sites flanking this area can pause the progression of replication forks, thereby allowing forks to enter but not to leave. Transcription of all required genes has to take place simultaneously with genome duplication. As both of these genome trafficking processes share the same template, conflicts are unavoidable. In this review, we focus on recent attempts to add additional origins into various ectopic chromosomal locations of the E. coli chromosome. As ectopic origins disturb the native replichore arrangements, the problems resulting from such perturbations can give important insights into how genome trafficking processes are coordinated and the problems that arise if this coordination is disturbed. The data from these studies highlight that head-on replication–transcription conflicts are indeed highly problematic and multiple repair pathways are required to restart replication forks arrested at obstacles. In addition, the existing data also demonstrate that the replication fork trap in E. coli imposes significant constraints to genome duplication if ectopic origins are active. We describe the current models of how replication fork fusion events can cause serious problems for genome duplication, as well as models of how such problems might be alleviated both by a number of repair pathways as well as the replication fork trap system. Considering the problems associated both with head-on replication-transcription conflicts as well as head-on replication fork fusion events might provide clues of how these genome trafficking issues have contributed to shape the distinct architecture of bacterial chromosomes.
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Affiliation(s)
- Aisha H Syeda
- Department of Biology, University of York, York, United Kingdom
| | - Juachi U Dimude
- Division of Biosciences, College of Health and Life Sciences, Brunel University London, Uxbridge, United Kingdom
| | - Ole Skovgaard
- Department of Science and Environment, Roskilde University, Roskilde, Denmark
| | - Christian J Rudolph
- Division of Biosciences, College of Health and Life Sciences, Brunel University London, Uxbridge, United Kingdom
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15
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Midgley-Smith SL, Dimude JU, Taylor T, Forrester NM, Upton AL, Lloyd RG, Rudolph CJ. Chromosomal over-replication in Escherichia coli recG cells is triggered by replication fork fusion and amplified if replichore symmetry is disturbed. Nucleic Acids Res 2019; 46:7701-7715. [PMID: 29982635 PMCID: PMC6125675 DOI: 10.1093/nar/gky566] [Citation(s) in RCA: 25] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2018] [Accepted: 06/13/2018] [Indexed: 01/04/2023] Open
Abstract
Chromosome duplication initiates via the assembly of replication forks at defined origins. Forks proceed in opposite directions until they fuse with a converging fork. Recent work highlights that fork fusions are highly choreographed both in pro- and eukaryotic cells. The circular Escherichia coli chromosome is replicated from a single origin (oriC), and a single fork fusion takes place in a specialised termination area opposite oriC that establishes a fork trap mediated by Tus protein bound at ter sequences that allows forks to enter but not leave. Here we further define the molecular details of fork fusions and the role of RecG helicase in replication termination. Our data support the idea that fork fusions have the potential to trigger local re-replication of the already replicated DNA. In ΔrecG cells this potential is realised in a substantial fraction of cells and is dramatically elevated when one fork is trapped for some time before the converging fork arrives. They also support the idea that the termination area evolved to contain such over-replication and we propose that the stable arrest of replication forks at ter/Tus complexes is an important feature that limits the likelihood of problems arising as replication terminates.
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Affiliation(s)
- Sarah L Midgley-Smith
- Division of Biosciences, College of Health and Life Sciences, Brunel University London, Uxbridge UB8 3PH, UK
| | - Juachi U Dimude
- Division of Biosciences, College of Health and Life Sciences, Brunel University London, Uxbridge UB8 3PH, UK
| | - Toni Taylor
- Division of Biosciences, College of Health and Life Sciences, Brunel University London, Uxbridge UB8 3PH, UK
| | - Nicole M Forrester
- Division of Biosciences, College of Health and Life Sciences, Brunel University London, Uxbridge UB8 3PH, UK
| | - Amy L Upton
- Division of Biosciences, College of Health and Life Sciences, Brunel University London, Uxbridge UB8 3PH, UK
| | - Robert G Lloyd
- Medical School, Queen's Medical Centre, Nottingham University, Nottingham NG7 2UH, UK
| | - Christian J Rudolph
- Division of Biosciences, College of Health and Life Sciences, Brunel University London, Uxbridge UB8 3PH, UK
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16
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Replisome activity slowdown after exposure to ultraviolet light in Escherichia coli. Proc Natl Acad Sci U S A 2019; 116:11747-11753. [PMID: 31127046 DOI: 10.1073/pnas.1819297116] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023] Open
Abstract
The replisome is a multiprotein machine that is responsible for replicating DNA. During active DNA synthesis, the replisome tightly associates with DNA. In contrast, after DNA damage, the replisome may disassemble, exposing DNA to breaks and threatening cell survival. Using live cell imaging, we studied the effect of UV light on the replisome of Escherichia coli Surprisingly, our results showed an increase in Pol III holoenzyme (Pol III HE) foci post-UV that do not colocalize with the DnaB helicase. Formation of these foci is independent of active replication forks and dependent on the presence of the χ subunit of the clamp loader, suggesting recruitment of Pol III HE at sites of DNA repair. Our results also showed a decrease of DnaB helicase foci per cell after UV, consistent with the disassembly of a fraction of the replisomes. By labeling newly synthesized DNA, we demonstrated that a drop in the rate of synthesis is not explained by replisome disassembly alone. Instead, we show that most replisomes continue synthesizing DNA at a slower rate after UV. We propose that the slowdown in replisome activity is a strategy to prevent clashes with engaged DNA repair proteins and preserve the integrity of the replication fork.
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17
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Sun Q, Jiao F, Lin G, Yu J, Tang M. The nonlinear dynamics and fluctuations of mRNA levels in cell cycle coupled transcription. PLoS Comput Biol 2019; 15:e1007017. [PMID: 31034470 PMCID: PMC6508750 DOI: 10.1371/journal.pcbi.1007017] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2018] [Revised: 05/09/2019] [Accepted: 04/10/2019] [Indexed: 12/02/2022] Open
Abstract
Gene transcription is a noisy process, and cell division cycle is an important source of gene transcription noise. In this work, we develop a mathematical approach by coupling transcription kinetics with cell division cycles to delineate how they are combined to regulate transcription output and noise. In view of gene dosage, a cell cycle is divided into an early stage S1 and a late stage S2. The analytical forms for the mean and the noise of mRNA numbers are given in each stage. The analysis based on these formulas predicts precisely the fold change r* of mRNA numbers from S1 to S2 measured in a mouse embryonic stem cell line. When transcription follows similar kinetics in both stages, r* buffers against DNA dosage variation and r* ∈ (1, 2). Numerical simulations suggest that increasing cell cycle durations up-regulates transcription with less noise, whereas rapid stage transitions induce highly noisy transcription. A minimization of the transcription noise is observed when transcription homeostasis is attained by varying a single kinetic rate. When the transcription level scales with cellular volume, either by reducing the transcription burst frequency or by increasing the burst size in S2, the noise shows only a minor variation over a wide range of cell cycle stage durations. The reduction level in the burst frequency is nearly a constant, whereas the increase in the burst size is conceivably sensitive, when responding to a large random variation of the cell cycle durations and the gene duplication time. Gene transcription in single cells is inherently a stochastic process, resulting in a large variability in the number of transcripts and constituting the phenotypic heterogeneity in cell population. Cell division cycle has global effects on transcriptional outputs, and is thought to be an additional source of transcription noise. In this work, we develop a hybrid model to delineate the combined contribution of transcription activities and cell divisions in the variability of transcript counts. By working with the analytical forms of the mean and the noise of mRNA numbers, we show that if the transcription kinetic rates do not change considerably, then the average mRNA level is increased about 1 to 2 folds from earlier to later cell cycle stages. When transcription homeostasis is attained by varying a single kinetic rate between the two cell cycle stages, we find no significant changes in the transcription noise, and the homeostasis nearly minimizes the noise. In our continuous study on the transcript concentration homeostasis that the transcription level scales with the cellular volume, we find only minor variations of the noise if the homeostasis is maintained either by reducing the transcription burst frequency or by increasing the burst size in late cell cycle phase, in the face of a large cell cycle stage duration variation. The reduction in the burst frequency is relative robust, while the increase in the burst size is conceivably sensitive, to the large random variation of the cell cycle durations and the gene duplication time.
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Affiliation(s)
- Qiwen Sun
- Center for Applied Mathematics, Guangzhou University, Guangzhou, 510006, China
- Department of Mathematics, Michigan State University, East Lansing, Michigan, United States of America
| | - Feng Jiao
- Center for Applied Mathematics, Guangzhou University, Guangzhou, 510006, China
- Department of Mathematics, Michigan State University, East Lansing, Michigan, United States of America
| | - Genghong Lin
- Center for Applied Mathematics, Guangzhou University, Guangzhou, 510006, China
- Department of Mathematics, Michigan State University, East Lansing, Michigan, United States of America
| | - Jianshe Yu
- Center for Applied Mathematics, Guangzhou University, Guangzhou, 510006, China
| | - Moxun Tang
- Department of Mathematics, Michigan State University, East Lansing, Michigan, United States of America
- * E-mail:
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18
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Abstract
Measuring biological data across time and space is critical for understanding complex biological processes and for various biosurveillance applications. However, such data are often inaccessible or difficult to directly obtain. Less invasive, more robust and higher-throughput biological recording tools are needed to profile cells and their environments. DNA-based cellular recording is an emerging and powerful framework for tracking intracellular and extracellular biological events over time across living cells and populations. Here, we review and assess DNA recorders that utilize CRISPR nucleases, integrases and base-editing strategies, as well as recombinase and polymerase-based methods. Quantitative characterization, modelling and evaluation of these DNA-recording modalities can guide their design and implementation for specific application areas.
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Affiliation(s)
- Ravi U Sheth
- Department of Systems Biology, Columbia University Medical Center, New York, NY, USA
- Integrated Program in Cellular, Molecular and Biomedical Studies, Columbia University, New York, NY, USA
| | - Harris H Wang
- Department of Systems Biology, Columbia University Medical Center, New York, NY, USA.
- Department of Pathology and Cell Biology, Columbia University Medical Center, New York, NY, USA.
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19
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Dimude JU, Midgley-Smith SL, Rudolph CJ. Replication-transcription conflicts trigger extensive DNA degradation in Escherichia coli cells lacking RecBCD. DNA Repair (Amst) 2018; 70:37-48. [PMID: 30145455 DOI: 10.1016/j.dnarep.2018.08.002] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2018] [Revised: 08/15/2018] [Accepted: 08/16/2018] [Indexed: 11/17/2022]
Abstract
Bacterial chromosome duplication is initiated at a single origin (oriC). Two forks are assembled and proceed in opposite directions with high speed and processivity until they fuse and terminate in a specialised area opposite to oriC. Proceeding forks are often blocked by tightly-bound protein-DNA complexes, topological strain or various DNA lesions. In Escherichia coli the RecBCD protein complex is a key player in the processing of double-stranded DNA (dsDNA) ends. It has important roles in the repair of dsDNA breaks and the restart of forks stalled at sites of replication-transcription conflicts. In addition, ΔrecB cells show substantial amounts of DNA degradation in the termination area. In this study we show that head-on encounters of replication and transcription at a highly-transcribed rrn operon expose fork structures to degradation by nucleases such as SbcCD. SbcCD is also mostly responsible for the degradation in the termination area of ΔrecB cells. However, additional processes exacerbate degradation specifically in this location. Replication profiles from ΔrecB cells in which the chromosome is linearized at two different locations highlight that the location of replication termination can have some impact on the degradation observed. Our data improve our understanding of the role of RecBCD at sites of replication-transcription conflicts as well as the final stages of chromosome duplication. However, they also highlight that current models are insufficient and cannot explain all the molecular details in cells lacking RecBCD.
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Affiliation(s)
- Juachi U Dimude
- Division of Biosciences, College of Health and Life Sciences, Brunel University London, Uxbridge, UB8 3PH, UK
| | - Sarah L Midgley-Smith
- Division of Biosciences, College of Health and Life Sciences, Brunel University London, Uxbridge, UB8 3PH, UK
| | - Christian J Rudolph
- Division of Biosciences, College of Health and Life Sciences, Brunel University London, Uxbridge, UB8 3PH, UK.
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20
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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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21
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Sinha AK, Possoz C, Durand A, Desfontaines JM, Barre FX, Leach DRF, Michel B. Broken replication forks trigger heritable DNA breaks in the terminus of a circular chromosome. PLoS Genet 2018. [PMID: 29522563 PMCID: PMC5862497 DOI: 10.1371/journal.pgen.1007256] [Citation(s) in RCA: 31] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
It was recently reported that the recBC mutants of Escherichia coli, deficient for DNA double-strand break (DSB) repair, have a decreased copy number of their terminus region. We previously showed that this deficit resulted from DNA loss after post-replicative breakage of one of the two sister-chromosome termini at cell division. A viable cell and a dead cell devoid of terminus region were thus produced and, intriguingly, the reaction was transmitted to the following generations. Using genome marker frequency profiling and observation by microscopy of specific DNA loci within the terminus, we reveal here the origin of this phenomenon. We observed that terminus DNA loss was reduced in a recA mutant by the double-strand DNA degradation activity of RecBCD. The terminus-less cell produced at the first cell division was less prone to divide than the one produced at the next generation. DNA loss was not heritable if the chromosome was linearized in the terminus and occurred at chromosome termini that were unable to segregate after replication. We propose that in a recB mutant replication fork breakage results in the persistence of a linear DNA tail attached to a circular chromosome. Segregation of the linear and circular parts of this "σ-replicating chromosome" causes terminus DNA breakage during cell division. One daughter cell inherits a truncated linear chromosome and is not viable. The other inherits a circular chromosome attached to a linear tail ending in the chromosome terminus. Replication extends this tail, while degradation of its extremity results in terminus DNA loss. Repeated generation and segregation of new σ-replicating chromosomes explains the heritability of post-replicative breakage. Our results allow us to determine that in E. coli at each generation, 18% of cells are subject to replication fork breakage at dispersed, potentially random, chromosomal locations.
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Affiliation(s)
- Anurag Kumar Sinha
- Bacterial DNA stability, Genome biology department, Institute for Integrative Biology of the Cell (I2BC), CEA, CNRS, Université Paris-Sud, Université Paris-Saclay, Gif-sur-Yvette, France
- * E-mail: (AKS); (BM)
| | - Christophe Possoz
- Evolution and maintenance of circular chromosomes, Genome biology department, Institute for Integrative Biology of the Cell (I2BC), CEA, CNRS, Université Paris-Sud, Université Paris-Saclay, Gif-sur-Yvette, France
| | - Adeline Durand
- Bacterial DNA stability, Genome biology department, Institute for Integrative Biology of the Cell (I2BC), CEA, CNRS, Université Paris-Sud, Université Paris-Saclay, Gif-sur-Yvette, France
| | - Jean-Michel Desfontaines
- Evolution and maintenance of circular chromosomes, Genome biology department, Institute for Integrative Biology of the Cell (I2BC), CEA, CNRS, Université Paris-Sud, Université Paris-Saclay, Gif-sur-Yvette, France
| | - François-Xavier Barre
- Evolution and maintenance of circular chromosomes, Genome biology department, Institute for Integrative Biology of the Cell (I2BC), CEA, CNRS, Université Paris-Sud, Université Paris-Saclay, Gif-sur-Yvette, France
| | - David R. F. Leach
- Institute of Cell Biology, School of Biological Sciences, University of Edinburgh, Edinburgh, United Kingdom
| | - Bénédicte Michel
- Bacterial DNA stability, Genome biology department, Institute for Integrative Biology of the Cell (I2BC), CEA, CNRS, Université Paris-Sud, Université Paris-Saclay, Gif-sur-Yvette, France
- * E-mail: (AKS); (BM)
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22
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Kamada K, Barillà D. Combing Chromosomal DNA Mediated by the SMC Complex: Structure and Mechanisms. Bioessays 2017; 40. [DOI: 10.1002/bies.201700166] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2017] [Revised: 10/29/2017] [Indexed: 12/16/2022]
Affiliation(s)
- Katsuhiko Kamada
- Chromosome Dynamics Laboratory; RIKEN; 2-1 Hirosawa; Wako Saitama 351-0198 Japan
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23
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Kono N, Tomita M, Arakawa K. eRP arrangement: a strategy for assembled genomic contig rearrangement based on replication profiling in bacteria. BMC Genomics 2017; 18:784. [PMID: 29029602 PMCID: PMC5640929 DOI: 10.1186/s12864-017-4162-z] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2017] [Accepted: 10/05/2017] [Indexed: 12/15/2022] Open
Abstract
Background The reduced cost of sequencing has made de novo sequencing and the assembly of draft microbial genomes feasible in any ordinary biology lab. However, the process of finishing and completing the genome remains labor-intensive and computationally challenging in some cases, such as in the study of complete genome sequences, genomic rearrangements, long-range syntenic relationships, and structural variations. Methods Here, we show a contig reordering strategy based on experimental replication profiling (eRP) to recapitulate the bacterial genome structure within draft genomes. During the exponential growth phase, the majority of bacteria show a global genomic copy number gradient that is enriched near the replication origin and gradually declines toward the terminus. Therefore, if genome sequencing is performed with appropriate timing, the short-read coverage reflects this copy number gradient, providing information about the contig positions relative to the replication origin and terminus. Results We therefore investigated the appropriate timing for genomic DNA sampling and developed an algorithm for the reordering of the contigs based on eRP. As a result, this strategy successfully recapitulates the genomic structure of various structural mutants with draft genome sequencing. Conclusions Our strategy was successful for contig rearrangement with intracellular DNA replication behavior mechanisms and can be applied to almost all bacteria because the DNA replication system is highly conserved. Therefore, eRP makes it possible to understand genomic structural information and long-range syntenic relationships using a draft genome that is based on short reads. Electronic supplementary material The online version of this article (10.1186/s12864-017-4162-z) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- Nobuaki Kono
- Institute for Advanced Biosciences, Keio University, Mizukami 246-2, Kakuganji, Tsuruoka, Yamagata, 997-0052, Japan.
| | - Masaru Tomita
- Institute for Advanced Biosciences, Keio University, Mizukami 246-2, Kakuganji, Tsuruoka, Yamagata, 997-0052, Japan
| | - Kazuharu Arakawa
- Institute for Advanced Biosciences, Keio University, Mizukami 246-2, Kakuganji, Tsuruoka, Yamagata, 997-0052, Japan
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24
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Abstract
Replication forks frequently are challenged by lesions on the DNA template, replication-impeding DNA secondary structures, tightly bound proteins or nucleotide pool imbalance. Studies in bacteria have suggested that under these circumstances the fork may leave behind single-strand DNA gaps that are subsequently filled by homologous recombination, translesion DNA synthesis or template-switching repair synthesis. This review focuses on the template-switching pathways and how the mechanisms of these processes have been deduced from biochemical and genetic studies. I discuss how template-switching can contribute significantly to genetic instability, including mutational hotspots and frequent genetic rearrangements, and how template-switching may be elicited by replication fork damage.
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Affiliation(s)
- Susan T Lovett
- Department of Biology and Rosenstiel Basic Medical Sciences Research Center, Brandeis University, Waltham, MA, 2454-9110, USA.
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25
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Abstract
It has been assumed that DNA synthesis by the leading- and lagging-strand polymerases in the replisome must be coordinated to avoid the formation of significant gaps in the nascent strands. Using real-time single-molecule analysis, we establish that leading- and lagging-strand DNA polymerases function independently within a single replisome. Although average rates of DNA synthesis on leading and lagging strands are similar, individual trajectories of both DNA polymerases display stochastically switchable rates of synthesis interspersed with distinct pauses. DNA unwinding by the replicative helicase may continue during such pauses, but a self-governing mechanism, where helicase speed is reduced by ∼80%, permits recoupling of polymerase to helicase. These features imply a more dynamic, kinetically discontinuous replication process, wherein contacts within the replisome are continually broken and reformed. We conclude that the stochastic behavior of replisome components ensures complete DNA duplication without requiring coordination of leading- and lagging-strand synthesis. PAPERCLIP.
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26
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Abstract
Ubiquitous conserved processes that repair DNA damage are essential for the maintenance and propagation of genomes over generations. Then again, inaccuracies in DNA transactions and failures to remove mutagenic lesions cause heritable genome changes. Building on decades of research using genetics and biochemistry, unprecedented quantitative insight into DNA repair mechanisms has come from the new-found ability to measure single proteins in vitro and inside individual living cells. This has brought together biologists, chemists, engineers, physicists, and mathematicians to solve long-standing questions about the way in which repair enzymes search for DNA lesions and form protein complexes that act in DNA repair pathways. Furthermore, unexpected discoveries have resulted from capabilities to resolve molecular heterogeneity and cell subpopulations, provoking new questions about the role of stochastic processes in DNA repair and mutagenesis. These studies are leading to new technologies that will find widespread use in basic research, biotechnology, and medicine.
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Affiliation(s)
- Stephan Uphoff
- Department of Biochemistry, University of Oxford, Oxford OX1 3QU, United Kingdom; ,
| | - David J Sherratt
- Department of Biochemistry, University of Oxford, Oxford OX1 3QU, United Kingdom; ,
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27
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Akiyama MT, Oshima T, Chumsakul O, Ishikawa S, Maki H. Replication fork progression is paused in two large chromosomal zones flanking the DNA replication origin in Escherichia coli. Genes Cells 2016; 21:907-14. [PMID: 27353572 DOI: 10.1111/gtc.12388] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2016] [Accepted: 05/16/2016] [Indexed: 11/27/2022]
Abstract
Although the speed of nascent DNA synthesis at individual replication forks is relatively uniform in bacterial cells, the dynamics of replication fork progression on the chromosome are hampered by a variety of natural impediments. Genome replication dynamics can be directly measured from an exponentially growing cell population by sequencing newly synthesized DNA strands that were specifically pulse-labeled with the thymidine analogue 5-bromo-2'-deoxyuridine (BrdU). However, a short pulse labeling with BrdU is impracticable for bacteria because of poor incorporation of BrdU into the cells, and thus, the genomewide dynamics of bacterial DNA replication remain undetermined. Using a new thymidine-requiring Escherichia coli strain, eCOMB, and high-throughput sequencing, we succeeded in determining the genomewide replication profile in bacterial cells. We also found that fork progression is paused in two ~200-kb chromosomal zones that flank the replication origin in the growing cells. This origin-proximal obstruction to fork progression was overcome by an increased thymidine concentration in the culture medium and enhanced by inhibition of transcription. These indicate that DNA replication near the origin is sensitive to the impediments to fork progression, namely a scarcity of the DNA precursor deoxythymidine triphosphate and probable conflicts between replication and transcription machineries.
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Affiliation(s)
- Masahiro Tatsumi Akiyama
- Division of Systems Biology, Graduate School of Biological Sciences, Nara Institute of Science and Technology, 8916-5 Takayama, Ikoma, Nara, 630-0192, Japan
| | - Taku Oshima
- Division of Systems Biology, Graduate School of Biological Sciences, Nara Institute of Science and Technology, 8916-5 Takayama, Ikoma, Nara, 630-0192, Japan
| | - Onuma Chumsakul
- Division of Systems Biology, Graduate School of Biological Sciences, Nara Institute of Science and Technology, 8916-5 Takayama, Ikoma, Nara, 630-0192, Japan
| | - Shu Ishikawa
- Division of Systems Biology, Graduate School of Biological Sciences, Nara Institute of Science and Technology, 8916-5 Takayama, Ikoma, Nara, 630-0192, Japan
| | - Hisaji Maki
- Division of Systems Biology, Graduate School of Biological Sciences, Nara Institute of Science and Technology, 8916-5 Takayama, Ikoma, Nara, 630-0192, Japan
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28
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Abstract
DNA replication in Escherichia coli initiates at oriC, the origin of replication and proceeds bidirectionally, resulting in two replication forks that travel in opposite directions from the origin. Here, we focus on events at the replication fork. The replication machinery (or replisome), first assembled on both forks at oriC, contains the DnaB helicase for strand separation, and the DNA polymerase III holoenzyme (Pol III HE) for DNA synthesis. DnaB interacts transiently with the DnaG primase for RNA priming on both strands. The Pol III HE is made up of three subassemblies: (i) the αɛθ core polymerase complex that is present in two (or three) copies to simultaneously copy both DNA strands, (ii) the β2 sliding clamp that interacts with the core polymerase to ensure its processivity, and (iii) the seven-subunit clamp loader complex that loads β2 onto primer-template junctions and interacts with the α polymerase subunit of the core and the DnaB helicase to organize the two (or three) core polymerases. Here, we review the structures of the enzymatic components of replisomes, and the protein-protein and protein-DNA interactions that ensure they remain intact while undergoing substantial dynamic changes as they function to copy both the leading and lagging strands simultaneously during coordinated replication.
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Affiliation(s)
- J S Lewis
- Centre for Medical & Molecular Bioscience, University of Wollongong, Wollongong, NSW, Australia
| | - S Jergic
- Centre for Medical & Molecular Bioscience, University of Wollongong, Wollongong, NSW, Australia
| | - N E Dixon
- Centre for Medical & Molecular Bioscience, University of Wollongong, Wollongong, NSW, Australia.
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29
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Tanaka T, Nishito Y, Masai H. Fork restart protein, PriA, binds around oriC after depletion of nucleotide precursors: Replication fork arrest near the replication origin. Biochem Biophys Res Commun 2016; 470:546-551. [PMID: 26801562 DOI: 10.1016/j.bbrc.2016.01.108] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2016] [Accepted: 01/17/2016] [Indexed: 11/19/2022]
Abstract
Arrest of replication fork progression is one of the most common causes for increasing the genomic instability. In bacteria, PriA, a conserved DEXH-type helicase, plays a major role in recognition of the stalled forks and restart of DNA replication. We took advantage of PriA's ability to specifically recognize stalled replication forks to determine the genomic loci where replication forks are prone to stall on the Escherichia coli genome. We found that PriA binds around oriC upon thymine starvation which reduces the nucleotide supply and causes replication fork stalling. PriA binding quickly disappeared upon readdition of thymine. Furthermore, BrdU was incorporated at around oriC upon release from thymine starvation. Our results indicate that reduced supply of DNA replication precursors causes replication fork stalling preferentially in the 600 kb segment centered at oriC. This suggests that replication of the vicinity of oriC requires higher level of nucleotide precursors. The results also point to a possibility of slow fork movement and/or the presence of multiple fork arrest signals within this segment. Indeed, we have identified rather strong fork stall/pausing signals symmetrically located at ∼50 kb away from oriC. We speculate that replication pausing and fork-slow-down shortly after initiation may represent a novel checkpoint that ensures the presence of sufficient nucleotide supply prior to commitment to duplication of the entire genome.
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Affiliation(s)
- Taku Tanaka
- Department of Genome Medicine, Tokyo Metropolitan Institute of Medical Science, 4-6-1 Kamikitazawa, Setagaya-ku, Tokyo 156-8506, Japan
| | - Yasumasa Nishito
- Basic Technology Research Center, Tokyo Metropolitan Institute of Medical Science, 4-6-1 Kamikitazawa, Setagaya-ku, Tokyo 156-8506, Japan
| | - Hisao Masai
- Department of Genome Medicine, Tokyo Metropolitan Institute of Medical Science, 4-6-1 Kamikitazawa, Setagaya-ku, Tokyo 156-8506, Japan.
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30
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Lai PJ, Lim CT, Le HP, Katayama T, Leach DRF, Furukohri A, Maki H. Long inverted repeat transiently stalls DNA replication by forming hairpin structures on both leading and lagging strands. Genes Cells 2016; 21:136-45. [PMID: 26738888 DOI: 10.1111/gtc.12326] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/12/2015] [Accepted: 11/18/2015] [Indexed: 11/27/2022]
Abstract
Long inverted repeats (LIRs), often found in eukaryotic genomes, are unstable in Escherichia coli where they are recognized by the SbcCD (the bacterial Mre11/Rad50 homologue), an endonuclease/exonuclease capable of cleaving hairpin DNA. It has long been postulated that LIRs form hairpin structures exclusively on the lagging-strand template during DNA replication, and SbcCD cleaves these hairpin-containing lagging strands to generate DNA double-strand breaks. Using a reconstituted oriC plasmid DNA replication system, we have examined how a replication fork behaves when it meets a LIR on DNA. We have shown that leading-strand synthesis stalls transiently within the upstream half of the LIR. Pausing of lagging-strand synthesis at the LIR was not clearly observed, but the pattern of priming sites for Okazaki fragment synthesis was altered within the downstream half of the LIR. We have found that the LIR on a replicating plasmid was cleaved by SbcCD with almost equal frequency on both the leading- and lagging-strand templates. These data strongly suggest that the LIR is readily converted to a cruciform DNA, before the arrival of the fork, creating SbcCD-sensitive hairpin structures on both leading and lagging strands. We propose a model for the replication-dependent extrusion of LIRs to form cruciform structures that transiently impede replication fork movement.
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Affiliation(s)
- Pey Jiun Lai
- Division of Systems Biology, Graduate School of Biological Sciences, Nara Institute of Science and Technology, Ikoma, Nara, 630-0192, Japan
| | - Chew Theng Lim
- Division of Systems Biology, Graduate School of Biological Sciences, Nara Institute of Science and Technology, Ikoma, Nara, 630-0192, Japan
| | - Hang Phuong Le
- Division of Systems Biology, Graduate School of Biological Sciences, Nara Institute of Science and Technology, Ikoma, Nara, 630-0192, Japan
| | - Tsutomu Katayama
- Department of Molecular Biology, Graduate School of Pharmaceutical Sciences, Kyushu University, Fukuoka, 812-8582, Japan
| | - David R F Leach
- Institute of Cell Biology, School of Biological Sciences, University of Edinburgh, Kings Buildings, Edinburgh, EH9 3JR, UK
| | - Asako Furukohri
- Division of Systems Biology, Graduate School of Biological Sciences, Nara Institute of Science and Technology, Ikoma, Nara, 630-0192, Japan
| | - Hisaji Maki
- Division of Systems Biology, Graduate School of Biological Sciences, Nara Institute of Science and Technology, Ikoma, Nara, 630-0192, Japan
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31
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Elshenawy MM, Jergic S, Xu ZQ, Sobhy MA, Takahashi M, Oakley AJ, Dixon NE, Hamdan SM. Replisome speed determines the efficiency of the Tus−Ter replication termination barrier. Nature 2015; 525:394-8. [DOI: 10.1038/nature14866] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/21/2015] [Accepted: 06/26/2015] [Indexed: 11/09/2022]
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32
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Tan KW, Pham TM, Furukohri A, Maki H, Akiyama MT. Recombinase and translesion DNA polymerase decrease the speed of replication fork progression during the DNA damage response in Escherichia coli cells. Nucleic Acids Res 2015; 43:1714-25. [PMID: 25628359 PMCID: PMC4330395 DOI: 10.1093/nar/gkv044] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
The SOS response is a DNA damage response pathway that serves as a general safeguard of genome integrity in bacteria. Extensive studies of the SOS response in Escherichia coli have contributed to establishing the key concepts of cellular responses to DNA damage. However, how the SOS response impacts on the dynamics of DNA replication fork movement remains unknown. We found that inducing the SOS response decreases the mean speed of individual replication forks by 30–50% in E. coli cells, leading to a 20–30% reduction in overall DNA synthesis. dinB and recA belong to a group of genes that are upregulated during the SOS response, and encode the highly conserved proteins DinB (also known as DNA polymerase IV) and RecA, which, respectively, specializes in translesion DNA synthesis and functions as the central recombination protein. Both genes were independently responsible for the SOS-dependent slowdown of replication fork progression. Furthermore, fork speed was reduced when each gene was ectopically expressed in SOS-uninduced cells to the levels at which they are expressed in SOS-induced cells. These results clearly indicate that the increased expression of dinB and recA performs a novel role in restraining the progression of an unperturbed replication fork during the SOS response.
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Affiliation(s)
- Kang Wei Tan
- Division of Systems Biology, Graduate School of Biological Sciences, Nara Institute of Science and Technology, 8916-5 Takayama, Ikoma, Nara 630-0192, Japan
| | - Tuan Minh Pham
- Division of Systems Biology, Graduate School of Biological Sciences, Nara Institute of Science and Technology, 8916-5 Takayama, Ikoma, Nara 630-0192, Japan
| | - Asako Furukohri
- Division of Systems Biology, Graduate School of Biological Sciences, Nara Institute of Science and Technology, 8916-5 Takayama, Ikoma, Nara 630-0192, Japan
| | - Hisaji Maki
- Division of Systems Biology, Graduate School of Biological Sciences, Nara Institute of Science and Technology, 8916-5 Takayama, Ikoma, Nara 630-0192, Japan
| | - Masahiro Tatsumi Akiyama
- Division of Systems Biology, Graduate School of Biological Sciences, Nara Institute of Science and Technology, 8916-5 Takayama, Ikoma, Nara 630-0192, Japan
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33
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Xi L, Cech TR. Inventory of telomerase components in human cells reveals multiple subpopulations of hTR and hTERT. Nucleic Acids Res 2014; 42:8565-77. [PMID: 24990373 PMCID: PMC4117779 DOI: 10.1093/nar/gku560] [Citation(s) in RCA: 99] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023] Open
Abstract
Telomerase is the ribonucleoprotein (RNP) enzyme that elongates telomeric DNA to compensate for the attrition occurring during each cycle of DNA replication. Knowing the levels of telomerase in continuously dividing cells is important for understanding how much telomerase is required for cell immortality. In this study, we measured the endogenous levels of the human telomerase RNP and its two key components, human telomerase RNA (hTR) and human telomerase reverse transcriptase (hTERT). We estimate ∼240 telomerase monomers per cell for HEK 293T and HeLa, a number similar to that of telomeres in late S phase. The subunits were in excess of RNPs (e.g. ∼1150 hTR and ∼500 hTERT molecules per HeLa cell), suggesting the existence of unassembled components. This hypothesis was tested by overexpressing individual subunits, which increased total telomerase activity as measured by the direct enzyme assay. Thus, there are subpopulations of both hTR and hTERT not assembled into telomerase but capable of being recruited. We also determined the specific activity of endogenous telomerase and of overexpressed super-telomerase both to be ∼60 nt incorporated per telomerase per minute, with Km(dGTP) ∼17 μM, indicating super-telomerase is as catalytically active as endogenous telomerase and is thus a good model for biochemical studies.
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Affiliation(s)
- Linghe Xi
- University of Colorado BioFrontiers Institute, Boulder, CO 80303, USA Department of Molecular, Cellular and Developmental Biology, University of Colorado, Boulder, CO 80309, USA
| | - Thomas R Cech
- University of Colorado BioFrontiers Institute, Boulder, CO 80303, USA Department of Molecular, Cellular and Developmental Biology, University of Colorado, Boulder, CO 80309, USA Howard Hughes Medical Institute and Department of Chemistry and Biochemistry, University of Colorado, Boulder, CO 80303, USA
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34
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Kono N, Arakawa K, Sato M, Yoshikawa H, Tomita M, Itaya M. Undesigned selection for replication termination of bacterial chromosomes. J Mol Biol 2014; 426:2918-27. [PMID: 24946150 DOI: 10.1016/j.jmb.2014.06.005] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2014] [Revised: 06/09/2014] [Accepted: 06/09/2014] [Indexed: 11/15/2022]
Abstract
The oriC DNA replication origin in bacterial chromosomes, the location of which appears to be physically identified, is genetically regulated by relevant molecular machinery. In contrast, the location of the terminus remains obscure for many bacterial replicons, except for terC, the proposed and well-studied chromosome termination site in certain bacteria. The terC locus, which is composed of specific sequences for its binding protein, is located at a site opposite from oriC, exhibiting a symmetric structure around the oriC-terC axis. Here, we investigated Bacillus subtilis 168 strains whose axes were hindered and found that the native terC function was robust. However, eradication of terminus region specific binding protein resulted in the natural terC sites not being used for termination; instead, new termini were selected at a location exactly opposite to oriC. We concluded that replication generally terminates at the loci where the two approaching replisomes meet. This site was automatically selected, and two replisomes moving at the same rate supported symmetrical chromosome structures relative to oriC. The rule, which was even validated by artificial chromosomes irrespective of oriC, should be general for replicons administered by two replisomes.
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Affiliation(s)
- Nobuaki Kono
- Institute for Advanced Biosciences, Keio University, Yamagata 997-0017, Japan.
| | - Kazuharu Arakawa
- Institute for Advanced Biosciences, Keio University, Yamagata 997-0017, Japan
| | - Mitsuru Sato
- Institute for Advanced Biosciences, Keio University, Yamagata 997-0017, Japan
| | - Hirofumi Yoshikawa
- Department of Bioscience, Tokyo University of Agriculture, Tokyo 156-8502, Japan
| | - Masaru Tomita
- Institute for Advanced Biosciences, Keio University, Yamagata 997-0017, Japan
| | - Mitsuhiro Itaya
- Institute for Advanced Biosciences, Keio University, Yamagata 997-0017, Japan.
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35
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Abstract
Evolutionary selection for optimal genome preservation, replication, and expression should yield similar chromosome organizations in any type of cells. And yet, the chromosome organization is surprisingly different between eukaryotes and prokaryotes. The nuclear versus cytoplasmic accommodation of genetic material accounts for the distinct eukaryotic and prokaryotic modes of genome evolution, but it falls short of explaining the differences in the chromosome organization. I propose that the two distinct ways to organize chromosomes are driven by the differences between the global-consecutive chromosome cycle of eukaryotes and the local-concurrent chromosome cycle of prokaryotes. Specifically, progressive chromosome segregation in prokaryotes demands a single duplicon per chromosome, while other "precarious" features of the prokaryotic chromosomes can be viewed as compensations for this severe restriction.
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