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Nautiyal A, Thakur M. Prokaryotic DNA Crossroads: Holliday Junction Formation and Resolution. ACS OMEGA 2024; 9:12515-12538. [PMID: 38524412 PMCID: PMC10956419 DOI: 10.1021/acsomega.3c09866] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 12/10/2023] [Revised: 02/04/2024] [Accepted: 02/09/2024] [Indexed: 03/26/2024]
Abstract
Cells are continually exposed to a multitude of internal and external stressors, which give rise to various types of DNA damage. To protect the integrity of their genetic material, cells are equipped with a repertoire of repair proteins that engage in various repair mechanisms, facilitated by intricate networks of protein-protein and protein-DNA interactions. Among these networks is the homologous recombination (HR) system, a molecular repair mechanism conserved in all three domains of life. On one hand, HR ensures high-fidelity, template-dependent DNA repair, while on the other hand, it results in the generation of combinatorial genetic variations through allelic exchange. Despite substantial progress in understanding this pathway in bacteria, yeast, and humans, several critical questions remain unanswered, including the molecular processes leading to the exchange of DNA segments, the coordination of protein binding, conformational switching during branch migration, and the resolution of Holliday Junctions (HJs). This Review delves into our current understanding of the HR pathway in bacteria, shedding light on the roles played by various proteins or their complexes at different stages of HR. In the first part of this Review, we provide a brief overview of the end resection processes and the strand-exchange reaction, offering a concise depiction of the mechanisms that culminate in the formation of HJs. In the latter half, we expound upon the alternative methods of branch migration and HJ resolution more comprehensively and holistically, considering the historical research timelines. Finally, when we consolidate our knowledge about HR within the broader context of genome replication and the emergence of resistant species, it becomes evident that the HR pathway is indispensable for the survival of bacteria in diverse ecological niches.
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Affiliation(s)
- Astha Nautiyal
- Department
of Biochemistry, Indian Institute of Science, Bangalore 560012, India
| | - Manoj Thakur
- Sri
Venkateswara College, Benito Juarez Road, University of Delhi, New Delhi 110021, India
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Schwarz MGA, Corrêa PR, Mendonça-Lima L. Transcriptional Profiling of Homologous Recombination Pathway Genes in Mycobacterium bovis BCG Moreau. Microorganisms 2023; 11:2534. [PMID: 37894192 PMCID: PMC10609372 DOI: 10.3390/microorganisms11102534] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2023] [Revised: 08/17/2023] [Accepted: 08/29/2023] [Indexed: 10/29/2023] Open
Abstract
Mycobacterium bovis BCG Moreau is the main Brazilian strain for vaccination against tuberculosis. It is considered an early strain, more like the original BCG, whereas BCG Pasteur, largely used as a reference, belongs to the late strain clade. BCG Moreau, contrary to Pasteur, is naturally deficient in homologous recombination (HR). In this work, using a UV exposure test, we aimed to detect differences in the survival of various BCG strains after DNA damage. Transcription of core and regulatory HR genes was further analyzed using RT-qPCR, aiming to identify the molecular agent responsible for this phenotype. We show that early strains share the Moreau low survival rate after UV exposure, whereas late strains mimic the Pasteur phenotype, indicating that this increase in HR efficiency is linked to the evolutionary clade history. Additionally, RT-qPCR shows that BCG Moreau has an overall lower level of these transcripts than Pasteur, indicating a correlation between this gene expression profile and HR efficiency. Further assays should be performed to fully identify the molecular mechanism that may explain this differential phenotype between early and late BCG strains.
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Affiliation(s)
- Marcos Gustavo Araujo Schwarz
- Laboratório de Biologia Molecular Aplicada à Micobactérias, Instituto Oswaldo Cruz, Fiocruz, Rio de Janeiro 21040-900, RJ, Brazil; (P.R.C.); (L.M.-L.)
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Wald J, Fahrenkamp D, Goessweiner-Mohr N, Lugmayr W, Ciccarelli L, Vesper O, Marlovits TC. Mechanism of AAA+ ATPase-mediated RuvAB-Holliday junction branch migration. Nature 2022; 609:630-639. [PMID: 36002576 PMCID: PMC9477746 DOI: 10.1038/s41586-022-05121-1] [Citation(s) in RCA: 16] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2021] [Accepted: 07/18/2022] [Indexed: 12/12/2022]
Abstract
The Holliday junction is a key intermediate formed during DNA recombination across all kingdoms of life1. In bacteria, the Holliday junction is processed by two homo-hexameric AAA+ ATPase RuvB motors, which assemble together with the RuvA-Holliday junction complex to energize the strand-exchange reaction2. Despite its importance for chromosome maintenance, the structure and mechanism by which this complex facilitates branch migration are unknown. Here, using time-resolved cryo-electron microscopy, we obtained structures of the ATP-hydrolysing RuvAB complex in seven distinct conformational states, captured during assembly and processing of a Holliday junction. Five structures together resolve the complete nucleotide cycle and reveal the spatiotemporal relationship between ATP hydrolysis, nucleotide exchange and context-specific conformational changes in RuvB. Coordinated motions in a converter formed by DNA-disengaged RuvB subunits stimulate hydrolysis and nucleotide exchange. Immobilization of the converter enables RuvB to convert the ATP-contained energy into a lever motion, which generates the pulling force driving the branch migration. We show that RuvB motors rotate together with the DNA substrate, which, together with a progressing nucleotide cycle, forms the mechanistic basis for DNA recombination by continuous branch migration. Together, our data decipher the molecular principles of homologous recombination by the RuvAB complex, elucidate discrete and sequential transition-state intermediates for chemo-mechanical coupling of hexameric AAA+ motors and provide a blueprint for the design of state-specific compounds targeting AAA+ motors.
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Affiliation(s)
- Jiri Wald
- Institute of Structural and Systems Biology, University Medical Center Hamburg-Eppendorf, Hamburg, Germany.
- Centre for Structural Systems Biology, Hamburg, Germany.
- Deutsches Elektronen Synchrotron (DESY), Hamburg, Germany.
- Institute of Molecular Biotechnology GmbH (IMBA), Austrian Academy of Sciences, Vienna, Austria.
- Research Institute of Molecular Pathology (IMP), Vienna, Austria.
| | - Dirk Fahrenkamp
- Institute of Structural and Systems Biology, University Medical Center Hamburg-Eppendorf, Hamburg, Germany.
- Centre for Structural Systems Biology, Hamburg, Germany.
- Deutsches Elektronen Synchrotron (DESY), Hamburg, Germany.
| | - Nikolaus Goessweiner-Mohr
- Institute of Structural and Systems Biology, University Medical Center Hamburg-Eppendorf, Hamburg, Germany
- Centre for Structural Systems Biology, Hamburg, Germany
- Deutsches Elektronen Synchrotron (DESY), Hamburg, Germany
- Institute of Molecular Biotechnology GmbH (IMBA), Austrian Academy of Sciences, Vienna, Austria
- Research Institute of Molecular Pathology (IMP), Vienna, Austria
- Institute of Biophysics, Johannes Kepler University (JKU), Linz, Austria
| | - Wolfgang Lugmayr
- Institute of Structural and Systems Biology, University Medical Center Hamburg-Eppendorf, Hamburg, Germany
- Centre for Structural Systems Biology, Hamburg, Germany
- Deutsches Elektronen Synchrotron (DESY), Hamburg, Germany
- Institute of Molecular Biotechnology GmbH (IMBA), Austrian Academy of Sciences, Vienna, Austria
- Research Institute of Molecular Pathology (IMP), Vienna, Austria
| | - Luciano Ciccarelli
- Institute of Structural and Systems Biology, University Medical Center Hamburg-Eppendorf, Hamburg, Germany
- Centre for Structural Systems Biology, Hamburg, Germany
- Institute of Molecular Biotechnology GmbH (IMBA), Austrian Academy of Sciences, Vienna, Austria
- Research Institute of Molecular Pathology (IMP), Vienna, Austria
- GlaxoSmithKline Vaccines, Siena, Italy
| | - Oliver Vesper
- Institute of Structural and Systems Biology, University Medical Center Hamburg-Eppendorf, Hamburg, Germany
- Centre for Structural Systems Biology, Hamburg, Germany
- Deutsches Elektronen Synchrotron (DESY), Hamburg, Germany
- Institute of Molecular Biotechnology GmbH (IMBA), Austrian Academy of Sciences, Vienna, Austria
- Research Institute of Molecular Pathology (IMP), Vienna, Austria
| | - Thomas C Marlovits
- Institute of Structural and Systems Biology, University Medical Center Hamburg-Eppendorf, Hamburg, Germany.
- Centre for Structural Systems Biology, Hamburg, Germany.
- Deutsches Elektronen Synchrotron (DESY), Hamburg, Germany.
- Institute of Molecular Biotechnology GmbH (IMBA), Austrian Academy of Sciences, Vienna, Austria.
- Research Institute of Molecular Pathology (IMP), Vienna, Austria.
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Bespyatykh J, Bespiatykh D, Malakhova M, Klimina K, Bespyatykh A, Varizhuk A, Tevyashova A, Nikolenko T, Pozmogova G, Ilina E, Shitikov E. Aureolic Acid Group of Agents as Potential Antituberculosis Drugs. Antibiotics (Basel) 2020; 9:E715. [PMID: 33086595 PMCID: PMC7650759 DOI: 10.3390/antibiotics9100715] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2020] [Revised: 10/15/2020] [Accepted: 10/16/2020] [Indexed: 11/16/2022] Open
Abstract
Mycobacterium tuberculosis is one of the most dangerous pathogens. Bacterial resistance to antituberculosis drugs grows each year, but searching for new drugs is a long process. Testing for available drugs to find active against mycobacteria may be a good alternative. In this work, antibiotics of the aureolic acid group were tested on a model organism Mycobacterium smegmatis. We presumed that antibiotics of this group may be potential G4 ligands. However, this was not confirmed in our analyses. We determined the antimicrobial activity of these drugs and revealed morphological changes in the cell structure upon treatment. Transcriptomic analysis documented increased expression of MSMEG_3743/soj and MSMEG_4228/ftsW, involved in cell division. Therefore, drugs may affect cell division, possibly disrupting the function of the Z-ring and the formation of a septum. Additionally, a decrease in the transcription level of several indispensable genes, such as nitrate reductase subunits (MSMEG_5137/narI and MSMEG_5139/narX) and MSMEG_3205/hisD was shown. We concluded that the mechanism of action of aureolic acid and its related compounds may be similar to that bedaquiline and disturb the NAD+/NADH balance in the cell. All of this allowed us to conclude that aureolic acid derivatives can be considered as potential antituberculosis drugs.
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Affiliation(s)
- Julia Bespyatykh
- Federal Research and Clinical Centre of Physical-Chemical Medicine, 119435 Moscow, Russia; (D.B.); (M.M.); (K.K.); (A.V.); (T.N.); (G.P.); (E.I.); (E.S.)
| | - Dmitry Bespiatykh
- Federal Research and Clinical Centre of Physical-Chemical Medicine, 119435 Moscow, Russia; (D.B.); (M.M.); (K.K.); (A.V.); (T.N.); (G.P.); (E.I.); (E.S.)
| | - Maja Malakhova
- Federal Research and Clinical Centre of Physical-Chemical Medicine, 119435 Moscow, Russia; (D.B.); (M.M.); (K.K.); (A.V.); (T.N.); (G.P.); (E.I.); (E.S.)
| | - Ksenia Klimina
- Federal Research and Clinical Centre of Physical-Chemical Medicine, 119435 Moscow, Russia; (D.B.); (M.M.); (K.K.); (A.V.); (T.N.); (G.P.); (E.I.); (E.S.)
| | - Andrey Bespyatykh
- Institute of Fundamental Medicine and Biology, Kazan Federal University, 420008 Kazan, Russia;
| | - Anna Varizhuk
- Federal Research and Clinical Centre of Physical-Chemical Medicine, 119435 Moscow, Russia; (D.B.); (M.M.); (K.K.); (A.V.); (T.N.); (G.P.); (E.I.); (E.S.)
| | | | - Tatiana Nikolenko
- Federal Research and Clinical Centre of Physical-Chemical Medicine, 119435 Moscow, Russia; (D.B.); (M.M.); (K.K.); (A.V.); (T.N.); (G.P.); (E.I.); (E.S.)
- Moscow Institute of Physics and Technology, Dolgoprudny, 141700 Moscow, Russia
| | - Galina Pozmogova
- Federal Research and Clinical Centre of Physical-Chemical Medicine, 119435 Moscow, Russia; (D.B.); (M.M.); (K.K.); (A.V.); (T.N.); (G.P.); (E.I.); (E.S.)
| | - Elena Ilina
- Federal Research and Clinical Centre of Physical-Chemical Medicine, 119435 Moscow, Russia; (D.B.); (M.M.); (K.K.); (A.V.); (T.N.); (G.P.); (E.I.); (E.S.)
| | - Egor Shitikov
- Federal Research and Clinical Centre of Physical-Chemical Medicine, 119435 Moscow, Russia; (D.B.); (M.M.); (K.K.); (A.V.); (T.N.); (G.P.); (E.I.); (E.S.)
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Singh A. Guardians of the mycobacterial genome: A review on DNA repair systems in Mycobacterium tuberculosis. MICROBIOLOGY-SGM 2017; 163:1740-1758. [PMID: 29171825 DOI: 10.1099/mic.0.000578] [Citation(s) in RCA: 31] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
The genomic integrity of Mycobacterium tuberculosis is continuously threatened by the harsh survival conditions inside host macrophages, due to immune and antibiotic stresses. Faithful genome maintenance and repair must be accomplished under stress for the bacillus to survive in the host, necessitating a robust DNA repair system. The importance of DNA repair systems in pathogenesis is well established. Previous examination of the M. tuberculosis genome revealed homologues of almost all the major DNA repair systems, i.e. nucleotide excision repair (NER), base excision repair (BER), homologous recombination (HR) and non-homologous end joining (NHEJ). However, recent developments in the field have pointed to the presence of novel proteins and pathways in mycobacteria. Homologues of archeal mismatch repair proteins were recently reported in mycobacteria, a pathway previously thought to be absent. RecBCD, the major nuclease-helicase enzymes involved in HR in E. coli, were implicated in the single-strand annealing (SSA) pathway. Novel roles of archeo-eukaryotic primase (AEP) polymerases, previously thought to be exclusive to NHEJ, have been reported in BER. Many new proteins with a probable role in DNA repair have also been discovered. It is now realized that the DNA repair systems in M. tuberculosis are highly evolved and have redundant backup mechanisms to mend the damage. This review is an attempt to summarize our current understanding of the DNA repair systems in M. tuberculosis.
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Affiliation(s)
- Amandeep Singh
- Molecular Biophysics Unit, Indian Institute of Science, Bangalore 560012, Karnataka, India
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Abstract
Discontinuity of both strands of the chromosome is a lethal event in all living organisms because it compromises chromosome replication. As such, a diversity of DNA repair systems has evolved to repair double-strand DNA breaks (DSBs). In part, this diversity of DSB repair systems has evolved to repair breaks that arise in diverse physiologic circumstances or sequence contexts, including cellular states of nonreplication or breaks that arise between repeats. Mycobacteria elaborate a set of three genetically distinct DNA repair pathways: homologous recombination, nonhomologous end joining, and single-strand annealing. As such, mycobacterial DSB repair diverges substantially from the standard model of prokaryotic DSB repair and represents an attractive new model system. In addition, the presence in mycobacteria of a DSB repair system that can repair DSBs in nonreplicating cells (nonhomologous end joining) or when DSBs arise between repeats (single-strand annealing) has clear potential relevance to Mycobacterium tuberculosis pathogenesis, although the exact role of these systems in M. tuberculosis pathogenesis is still being elucidated. In this article we will review the genetics of mycobacterial DSB repair systems, focusing on recent insights.
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Thakur RS, Basavaraju S, Khanduja JS, Muniyappa K, Nagaraju G. Mycobacterium tuberculosis RecG protein but not RuvAB or RecA protein is efficient at remodeling the stalled replication forks: implications for multiple mechanisms of replication restart in mycobacteria. J Biol Chem 2015; 290:24119-39. [PMID: 26276393 DOI: 10.1074/jbc.m115.671164] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/09/2015] [Indexed: 11/06/2022] Open
Abstract
Aberrant DNA replication, defects in the protection, and restart of stalled replication forks are major causes of genome instability in all organisms. Replication fork reversal is emerging as an evolutionarily conserved physiological response for restart of stalled forks. Escherichia coli RecG, RuvAB, and RecA proteins have been shown to reverse the model replication fork structures in vitro. However, the pathways and the mechanisms by which Mycobacterium tuberculosis, a slow growing human pathogen, responds to different types of replication stress and DNA damage are unclear. Here, we show that M. tuberculosis RecG rescues E. coli ΔrecG cells from replicative stress. The purified M. tuberculosis RecG (MtRecG) and RuvAB (MtRuvAB) proteins catalyze fork reversal of model replication fork structures with and without a leading strand single-stranded DNA gap. Interestingly, single-stranded DNA-binding protein suppresses the MtRecG- and MtRuvAB-mediated fork reversal with substrates that contain lagging strand gap. Notably, our comparative studies with fork structures containing template damage and template switching mechanism of lesion bypass reveal that MtRecG but not MtRuvAB or MtRecA is proficient in driving the fork reversal. Finally, unlike MtRuvAB, we find that MtRecG drives efficient reversal of forks when fork structures are tightly bound by protein. These results provide direct evidence and valuable insights into the underlying mechanism of MtRecG-catalyzed replication fork remodeling and restart pathways in vivo.
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Affiliation(s)
- Roshan Singh Thakur
- From the Department of Biochemistry, Indian Institute of Science, Bangalore-560012, India
| | - Shivakumar Basavaraju
- From the Department of Biochemistry, Indian Institute of Science, Bangalore-560012, India
| | - Jasbeer Singh Khanduja
- From the Department of Biochemistry, Indian Institute of Science, Bangalore-560012, India
| | - K Muniyappa
- From the Department of Biochemistry, Indian Institute of Science, Bangalore-560012, India
| | - Ganesh Nagaraju
- From the Department of Biochemistry, Indian Institute of Science, Bangalore-560012, India
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Thakur RS, Basavaraju S, Somyajit K, Jain A, Subramanya S, Muniyappa K, Nagaraju G. Evidence for the role of Mycobacterium tuberculosis RecG helicase in DNA repair and recombination. FEBS J 2013; 280:1841-60. [PMID: 23438087 DOI: 10.1111/febs.12208] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2012] [Revised: 02/05/2013] [Accepted: 02/18/2013] [Indexed: 11/28/2022]
Abstract
In order to survive and replicate in a variety of stressful conditions during its life cycle, Mycobacterium tuberculosis must possess mechanisms to safeguard the integrity of the genome. Although DNA repair and recombination related genes are thought to play key roles in the repair of damaged DNA in all organisms, so far only a few of them have been functionally characterized in the tubercle bacillus. In this study, we show that M. tuberculosis RecG (MtRecG) expression was induced in response to different genotoxic agents. Strikingly, expression of MtRecG in Escherichia coli ∆recG mutant strain provided protection against mitomycin C, methyl methane sulfonate and UV induced cell death. Purified MtRecG exhibited higher binding affinity for the Holliday junction (HJ) compared with a number of canonical recombinational DNA repair intermediates. Notably, although MtRecG binds at the core of the mobile and immobile HJs, and with higher binding affinity for the immobile HJ, branch migration was evident only in the case of the mobile HJ. Furthermore, immobile HJs stimulate MtRecG ATPase activity less efficiently than mobile HJs. In addition to HJ substrates, MtRecG exhibited binding affinity for a variety of branched DNA structures including three-way junctions, replication forks, flap structures, forked duplex and a D-loop structure, but demonstrated strong unwinding activity on replication fork and flap DNA structures. Together, these results support that MtRecG plays an important role in processes related to DNA metabolism under normal as well as stress conditions.
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Affiliation(s)
- Roshan S Thakur
- Department of Biochemistry, Indian Institute of Science, Bangalore, India
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Bioconversion of crude glycerol by fungi. Appl Microbiol Biotechnol 2012; 93:1865-75. [DOI: 10.1007/s00253-012-3921-7] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2011] [Revised: 01/20/2012] [Accepted: 01/23/2012] [Indexed: 10/14/2022]
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Khanduja JS, Muniyappa K. Functional analysis of DNA replication fork reversal catalyzed by Mycobacterium tuberculosis RuvAB proteins. J Biol Chem 2012; 287:1345-60. [PMID: 22094465 PMCID: PMC3256873 DOI: 10.1074/jbc.m111.304741] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2011] [Revised: 11/14/2011] [Indexed: 11/06/2022] Open
Abstract
Initially discovered in Escherichia coli, RuvAB proteins are ubiquitous in bacteria and play a dual role as molecular motor proteins responsible for branch migration of the Holliday junction(s) and reversal of stalled replication forks. Despite mounting genetic evidence for a crucial role of RuvA and RuvB proteins in reversal of stalled replication forks, the mechanistic aspects of this process are still not fully understood. Here, we elucidate the ability of Mycobacterium tuberculosis RuvAB (MtRuvAB) complex to catalyze the reversal of replication forks using a range of DNA replication fork substrates. Our studies show that MtRuvAB, unlike E. coli RuvAB, is able to drive replication fork reversal via the formation of Holliday junction intermediates, suggesting that RuvAB-catalyzed fork reversal involves concerted unwinding and annealing of nascent leading and lagging strands. We also demonstrate the reversal of replication forks carrying hemi-replicated DNA, indicating that MtRuvAB complex-catalyzed fork reversal is independent of symmetry at the fork junction. The fork reversal reaction catalyzed by MtRuvAB is coupled to ATP hydrolysis, is processive, and culminates in the formation of an extended reverse DNA arm. Notably, we found that sequence heterology failed to impede the fork reversal activity of MtRuvAB. We discuss the implications of these results in the context of recognition and processing of varied types of replication fork structures by RuvAB proteins.
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Affiliation(s)
- Jasbeer Singh Khanduja
- From the Department of Biochemistry, Indian Institute of Science, Bangalore 560012, India
| | - K. Muniyappa
- From the Department of Biochemistry, Indian Institute of Science, Bangalore 560012, India
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Singh P, Patil KN, Khanduja JS, Kumar PS, Williams A, Rossi F, Rizzi M, Davis EO, Muniyappa K. Mycobacterium tuberculosis UvrD1 and UvrA proteins suppress DNA strand exchange promoted by cognate and noncognate RecA proteins. Biochemistry 2010; 49:4872-83. [PMID: 20455546 DOI: 10.1021/bi902021d] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
DNA helicases are present in all kingdoms of life and play crucial roles in processes of DNA metabolism such as replication, repair, recombination, and transcription. To date, however, the role of DNA helicases during homologous recombination in mycobacteria remains unknown. In this study, we show that Mycobacterium tuberculosis UvrD1 more efficiently inhibited the strand exchange promoted by its cognate RecA, compared to noncognate Mycobacterium smegmatis or Escherichia coli RecA proteins. The M. tuberculosis UvrD1(Q276R) mutant lacking the helicase and ATPase activities was able to block strand exchange promoted by mycobacterial RecA proteins but not of E. coli RecA. We observed that M. tuberculosis UvrA by itself has no discernible effect on strand exchange promoted by E. coli RecA but impedes the reaction catalyzed by the mycobacterial RecA proteins. Our data also show that M. tuberculosis UvrA and UvrD1 can act together to inhibit strand exchange promoted by mycobacterial RecA proteins. Taken together, these findings raise the possibility that UvrD1 and UvrA might act together in vivo to counter the deleterious effects of RecA nucleoprotein filaments and/or facilitate the dissolution of recombination intermediates. Finally, we provide direct experimental evidence for a physical interaction between M. tuberculosis UvrD1 and RecA on one hand and RecA and UvrA on the other hand. These observations are consistent with a molecular mechanism, whereby M. tuberculosis UvrA and UvrD1, acting together, block DNA strand exchange promoted by cognate and noncognate RecA proteins.
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Affiliation(s)
- Pawan Singh
- Department of Biochemistry, Indian Institute of Science, Bangalore 560012, India
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