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Sabei A, Prentiss M, Prévost C. Modeling the Homologous Recombination Process: Methods, Successes and Challenges. Int J Mol Sci 2023; 24:14896. [PMID: 37834348 PMCID: PMC10573387 DOI: 10.3390/ijms241914896] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2023] [Revised: 09/24/2023] [Accepted: 09/25/2023] [Indexed: 10/15/2023] Open
Abstract
Homologous recombination (HR) is a fundamental process common to all species. HR aims to faithfully repair DNA double strand breaks. HR involves the formation of nucleoprotein filaments on DNA single strands (ssDNA) resected from the break. The nucleoprotein filaments search for homologous regions in the genome and promote strand exchange with the ssDNA homologous region in an unbroken copy of the genome. HR has been the object of intensive studies for decades. Because multi-scale dynamics is a fundamental aspect of this process, studying HR is highly challenging, both experimentally and using computational approaches. Nevertheless, knowledge has built up over the years and has recently progressed at an accelerated pace, borne by increasingly focused investigations using new techniques such as single molecule approaches. Linking this knowledge to the atomic structure of the nucleoprotein filament systems and the succession of unstable, transient intermediate steps that takes place during the HR process remains a challenge; modeling retains a very strong role in bridging the gap between structures that are stable enough to be observed and in exploring transition paths between these structures. However, working on ever-changing long filament systems submitted to kinetic processes is full of pitfalls. This review presents the modeling tools that are used in such studies, their possibilities and limitations, and reviews the advances in the knowledge of the HR process that have been obtained through modeling. Notably, we will emphasize how cooperative behavior in the HR nucleoprotein filament enables modeling to produce reliable information.
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Affiliation(s)
- Afra Sabei
- CNRS, UPR 9080, Laboratoire de Biochimie Théorique, Université de Paris, 13 Rue Pierre et Marie Curie, F-75005 Paris, France;
- Institut de Biologie Physico-Chimique-Fondation Edmond de Rotschild, PSL Research University, F-75005 Paris, France
| | - Mara Prentiss
- Department of Physics, Harvard University, Cambridge, MA02138, USA;
| | - Chantal Prévost
- CNRS, UPR 9080, Laboratoire de Biochimie Théorique, Université de Paris, 13 Rue Pierre et Marie Curie, F-75005 Paris, France;
- Institut de Biologie Physico-Chimique-Fondation Edmond de Rotschild, PSL Research University, F-75005 Paris, France
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2
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Morrical SW. DNA-pairing and annealing processes in homologous recombination and homology-directed repair. Cold Spring Harb Perspect Biol 2015; 7:a016444. [PMID: 25646379 DOI: 10.1101/cshperspect.a016444] [Citation(s) in RCA: 94] [Impact Index Per Article: 10.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
The formation of heteroduplex DNA is a central step in the exchange of DNA sequences via homologous recombination, and in the accurate repair of broken chromosomes via homology-directed repair pathways. In cells, heteroduplex DNA largely arises through the activities of recombination proteins that promote DNA-pairing and annealing reactions. Classes of proteins involved in pairing and annealing include RecA-family DNA-pairing proteins, single-stranded DNA (ssDNA)-binding proteins, recombination mediator proteins, annealing proteins, and nucleases. This review explores the properties of these pairing and annealing proteins, and highlights their roles in complex recombination processes including the double Holliday junction (DhJ) formation, synthesis-dependent strand annealing, and single-strand annealing pathways--DNA transactions that are critical both for genome stability in individual organisms and for the evolution of species.
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Affiliation(s)
- Scott W Morrical
- Department of Biochemistry, University of Vermont College of Medicine, Burlington, Vermont 05405
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3
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Kates-Harbeck J, Tilloy A, Prentiss M. Simplified biased random walk model for RecA-protein-mediated homology recognition offers rapid and accurate self-assembly of long linear arrays of binding sites. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2013; 88:012702. [PMID: 23944487 PMCID: PMC4974998 DOI: 10.1103/physreve.88.012702] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/12/2012] [Indexed: 06/02/2023]
Abstract
Inspired by RecA-protein-based homology recognition, we consider the pairing of two long linear arrays of binding sites. We propose a fully reversible, physically realizable biased random walk model for rapid and accurate self-assembly due to the spontaneous pairing of matching binding sites, where the statistics of the searched sample are included. In the model, there are two bound conformations, and the free energy for each conformation is a weakly nonlinear function of the number of contiguous matched bound sites.
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Affiliation(s)
| | | | - Mara Prentiss
- Department of Physics, Harvard University, Cambridge, Massachusetts 02138, USA
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4
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Vlassakis J, Feinstein E, Yang D, Tilloy A, Weiller D, Kates-Harbeck J, Coljee V, Prentiss M. Tension on dsDNA bound to ssDNA-RecA filaments may play an important role in driving efficient and accurate homology recognition and strand exchange. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2013; 87:032702. [PMID: 27499708 PMCID: PMC4973255 DOI: 10.1103/physreve.87.032702] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
It is well known that during homology recognition and strand exchange the double stranded DNA (dsDNA) in DNA/RecA filaments is highly extended, but the functional role of the extension has been unclear. We present an analytical model that calculates the distribution of tension in the extended dsDNA during strand exchange. The model suggests that the binding of additional dsDNA base pairs to the DNA/RecA filament alters the tension in dsDNA that was already bound to the filament, resulting in a non-linear increase in the mechanical energy as a function of the number of bound base pairs. This collective mechanical response may promote homology stringency and underlie unexplained experimental results.
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Affiliation(s)
- Julea Vlassakis
- Harvard University, Department of Physics, Cambridge, MA, 02138
| | | | - Darren Yang
- Harvard University, Department of Physics, Cambridge, MA, 02138
| | - Antoine Tilloy
- Harvard University, Department of Physics, Cambridge, MA, 02138
| | - Dominic Weiller
- Harvard University, Department of Physics, Cambridge, MA, 02138
| | | | - Vincent Coljee
- Harvard University, Department of Physics, Cambridge, MA, 02138
| | - Mara Prentiss
- Harvard University, Department of Physics, Cambridge, MA, 02138
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5
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Ragunathan K, Joo C, Ha T. Real-time observation of strand exchange reaction with high spatiotemporal resolution. Structure 2011; 19:1064-73. [PMID: 21827943 DOI: 10.1016/j.str.2011.06.009] [Citation(s) in RCA: 54] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2011] [Revised: 05/23/2011] [Accepted: 06/07/2011] [Indexed: 11/25/2022]
Abstract
RecA binds to single-stranded (ss) DNA to form a helical filament that catalyzes strand exchange with a homologous double-stranded (ds) DNA. The study of strand exchange in ensemble assays is limited by the diffusion limited homology search process, which masks the subsequent strand exchange reaction. We developed a single-molecule fluorescence assay with a few base-pair and millisecond resolution that can separate initial docking from the subsequent propagation of joint molecule formation. Our data suggest that propagation occurs in 3 bp increments with destabilization of the incoming dsDNA and concomitant pairing with the reference ssDNA. Unexpectedly, we discovered the formation of a dynamic complex between RecA and the displaced DNA that remains bound transiently after joint molecule formation. This finding could have important implications for the irreversibility of strand exchange. Our model for strand exchange links structural models of RecA to its catalytic function.
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Affiliation(s)
- Kaushik Ragunathan
- Center for Biophysics and Computational Biology, Department of Physics, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA
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6
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Rojsitthisak P, Jongaroonngamsang N, Romero RM, Haworth IS. HPLC-UV, MALDI-TOF-MS and ESI-MS/MS analysis of the mechlorethamine DNA crosslink at a cytosine-cytosine mismatch pair. PLoS One 2011; 6:e20745. [PMID: 21673963 PMCID: PMC3108972 DOI: 10.1371/journal.pone.0020745] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2010] [Accepted: 05/12/2011] [Indexed: 01/19/2023] Open
Abstract
Background Mechlorethamine [ClCH2CH2N(CH3)CH2CH2Cl], a nitrogen mustard alkylating agent, has been proven to form a DNA interstrand crosslink at a cytosine-cytosine (C-C) mismatch pair using gel electrophoresis. However, the atomic connectivity of this unusual crosslink is unknown. Methodology/Principal Findings HPLC-UV, MALDI-TOF-MS, and ESI-MS/MS were used to determine the atomic connectivity of the DNA C-C crosslink formed by mechlorethamine, MALDI-TOF-MS of the HPLC-purified reaction product of mechlorethamine with the DNA duplex d[CTCACACCGTGGTTC]•d[GAACCACCGTGTGAG] (underlined bases are a C-C mismatch pair) indicated formation of an interstrand crosslink at m/z 9222.088 [M−2H+Na]+. Following enzymatic digestion of the crosslinked duplex by snake venom phosphodiesterase and calf intestinal phosphatase, ESI-MS/MS indicated the presence of dC-mech-dC [mech = CH2CH2N(CH3)CH2CH2] at m/z 269.2 [M]2+ (expected m/z 269.6, exact mass 539.27) and its hydrolytic product dC-mech-OH at m/z 329.6 [M]+ (expected m/z 329.2). Fragmentation of dC-mech-dC gave product ions at m/z 294.3 and 236.9 [M]+, which are both due to loss of the 4-amino group of cytosine (as ammonia), in addition to dC and dC+HN(CH3)CH = CH2, respectively. The presence of m/z 269.2 [M]2+ and loss of ammonia exclude crosslink formation at cytosine N4 or O2 and indicate crosslinking through cytosine N3 with formation of two quaternary ammonium ions. Conclusions Our results provide an important addition to the literature, as the first example of the use of HPLC and MS for analysis of a DNA adduct at the N3 position of cytosine.
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Affiliation(s)
- Pornchai Rojsitthisak
- Department of Food and Pharmaceutical Chemistry, Faculty of Pharmaceutical Sciences, Chulalongkorn University, Bangkok, Thailand.
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Tsai YC, Wang Y, Urena DE, Kumar S, Chen J. Heterology tolerance and recognition of mismatched base pairs by human Rad51 protein. DNA Repair (Amst) 2011; 10:363-72. [PMID: 21239234 DOI: 10.1016/j.dnarep.2010.12.007] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2010] [Revised: 12/17/2010] [Accepted: 12/20/2010] [Indexed: 12/15/2022]
Abstract
Human Rad51 (hRad51) promoted homology recognition and subsequent strand exchange are the key steps in human homologous recombination mediated repair of DNA double-strand breaks. However, it is still not clear how hRad51 deals with sequence heterology between the two homologous chromosomes in eukaryotic cells, which would lead to mismatched base pairs after strand exchange. Excessive tolerance of sequence heterology may compromise the fidelity of repair of DNA double-strand breaks. In this study, fluorescence resonance energy transfer (FRET) was used to monitor the heterology tolerance of human Rad51 mediated strand exchange reactions, in real time, by introducing either G-T or I-C mismatched base pairs between the two homologous DNA strands. The strand exchange reactions were much more sensitive to G-T than to I-C base pairs. These results imply that the recognition of homology and the tolerance of heterology by hRad51 may depend on the local structural motif adopted by the base pairs participating in strand exchange. AnhRad51 mutant protein (hRad51K133R), deficient in ATP hydrolysis, showed greater heterology tolerance to both types of mismatch base pairing, suggesting that ATPase activity may be important for maintenance of high fidelity homologous recombination DNA repair.
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Affiliation(s)
- Yu-Cheng Tsai
- Department of Chemistry and Biochemistry, University of Delaware, Newark, DE 19716, USA
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8
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RecA-Mediated Homology Search as a Nearly Optimal Signal Detection System. Mol Cell 2010; 40:388-96. [DOI: 10.1016/j.molcel.2010.10.020] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2009] [Revised: 02/18/2010] [Accepted: 09/08/2010] [Indexed: 11/18/2022]
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9
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Saladin A, Amourda C, Poulain P, Férey N, Baaden M, Zacharias M, Delalande O, Prévost C. Modeling the early stage of DNA sequence recognition within RecA nucleoprotein filaments. Nucleic Acids Res 2010; 38:6313-23. [PMID: 20507912 PMCID: PMC2965220 DOI: 10.1093/nar/gkq459] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023] Open
Abstract
Homologous recombination is a fundamental process enabling the repair of double-strand breaks with a high degree of fidelity. In prokaryotes, it is carried out by RecA nucleofilaments formed on single-stranded DNA (ssDNA). These filaments incorporate genomic sequences that are homologous to the ssDNA and exchange the homologous strands. Due to the highly dynamic character of this process and its rapid propagation along the filament, the sequence recognition and strand exchange mechanism remains unknown at the structural level. The recently published structure of the RecA/DNA filament active for recombination (Chen et al., Mechanism of homologous recombination from the RecA-ssDNA/dsDNA structure, Nature 2008, 453, 489) provides a starting point for new exploration of the system. Here, we investigate the possible geometries of association of the early encounter complex between RecA/ssDNA filament and double-stranded DNA (dsDNA). Due to the huge size of the system and its dense packing, we use a reduced representation for protein and DNA together with state-of-the-art molecular modeling methods, including systematic docking and virtual reality simulations. The results indicate that it is possible for the double-stranded DNA to access the RecA-bound ssDNA while initially retaining its Watson–Crick pairing. They emphasize the importance of RecA L2 loop mobility for both recognition and strand exchange.
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Affiliation(s)
- Adrien Saladin
- Laboratoire de Biochimie Théorique, UPR 9080 CNRS, Institut de Biologie Physico-Chimique, 13 rue Pierre et Marie Curie, F-75005 Paris, MTI, France
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10
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Mani A, Braslavsky I, Arbel-Goren R, Stavans J. Caught in the act: the lifetime of synaptic intermediates during the search for homology on DNA. Nucleic Acids Res 2009; 38:2036-43. [PMID: 20044347 PMCID: PMC2847238 DOI: 10.1093/nar/gkp1177] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Homologous recombination plays pivotal roles in DNA repair and in the generation of genetic diversity. To locate homologous target sequences at which strand exchange can occur within a timescale that a cell’s biology demands, a single-stranded DNA-recombinase complex must search among a large number of sequences on a genome by forming synapses with chromosomal segments of DNA. A key element in the search is the time it takes for the two sequences of DNA to be compared, i.e. the synapse lifetime. Here, we visualize for the first time fluorescently tagged individual synapses formed by RecA, a prokaryotic recombinase, and measure their lifetime as a function of synapse length and differences in sequence between the participating DNAs. Surprisingly, lifetimes can be ∼10 s long when the DNAs are fully heterologous, and much longer for partial homology, consistently with ensemble FRET measurements. Synapse lifetime increases rapidly as the length of a region of full homology at either the 3′- or 5′-ends of the invading single-stranded DNA increases above 30 bases. A few mismatches can reduce dramatically the lifetime of synapses formed with nearly homologous DNAs. These results suggest the need for facilitated homology search mechanisms to locate homology successfully within the timescales observed in vivo.
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Affiliation(s)
- Adam Mani
- Department of Physics of Complex Systems, Weizmann Institute of Science, Rehovot 76100, Israel
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11
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Volodin AA, Bocharova TN, Smirnova EA, Camerini-Otero RD. Reversibility, equilibration, and fidelity of strand exchange reaction between short oligonucleotides promoted by RecA protein from escherichia coli and human Rad51 and Dmc1 proteins. J Biol Chem 2009; 284:1495-504. [PMID: 19004837 PMCID: PMC2615514 DOI: 10.1074/jbc.m800612200] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2008] [Revised: 10/21/2008] [Indexed: 11/06/2022] Open
Abstract
We demonstrate the reversibility of RecA-promoted strand exchange reaction between short oligonucleotides in the presence of adenosine 5'-O-(thiotriphosphate). The reverse reaction proceeds without the dissociation of RecA from DNA. The reaction reaches equilibrium and its yield depends on the homology between the reaction substrates. We estimate the tolerance of the RecA-promoted strand exchange to individual base substitutions for a comprehensive set of possible base combinations in a selected position along oligonucleotide substrates for strand exchange and find, in agreement with previously reported estimations, that this tolerance is higher than in the case of free DNA. It is demonstrated that the short oligonucleotide-based approach can be applied to the human recombinases Rad51 and Dmc1 when strand exchange is performed in the presence of calcium ions and ATP. Remarkably, despite the commonly held belief that the eukaryotic recombinases have an inherently lower strand exchange activity, in our system their efficiencies in strand exchange are comparable with that of RecA. Under our experimental conditions, the human recombinases exhibit a significantly higher tolerance to interruptions of homology due to point base substitutions than RecA. Finding conditions where a chemical reaction is reversible and reaches equilibrium is critically important for its thermodynamically correct description. We believe that the experimental system described here will substantially facilitate further studies on different aspects of the mechanisms of homologous recombination.
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Affiliation(s)
- Alexander A Volodin
- Institute of Molecular Genetics of the Russian Academy of Sciences, Kurchatov Square, 123182 Moscow, Russia
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12
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Bahr M, Gabelica V, Granzhan A, Teulade-Fichou MP, Weinhold E. Selective recognition of pyrimidine-pyrimidine DNA mismatches by distance-constrained macrocyclic bis-intercalators. Nucleic Acids Res 2008; 36:5000-12. [PMID: 18658249 PMCID: PMC2528167 DOI: 10.1093/nar/gkn392] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
Binding of three macrocyclic bis-intercalators, derivatives of acridine and naphthalene, and two acyclic model compounds to mismatch-containing and matched duplex oligodeoxynucleotides was analyzed by thermal denaturation experiments, electrospray ionization mass spectrometry studies (ESI-MS) and fluorescent intercalator displacement (FID) titrations. The macrocyclic bis-intercalators bind to duplexes containing mismatched thymine bases with high selectivity over the fully matched ones, whereas the acyclic model compounds are much less selective and strongly bind to the matched DNA. Moreover, the results from thermal denaturation experiments are in very good agreement with the binding affinities obtained by ESI-MS and FID measurements. The FID results also demonstrate that the macrocyclic naphthalene derivative BisNP preferentially binds to pyrimidine–pyrimidine mismatches compared to all other possible base mismatches. This ligand also efficiently competes with a DNA enzyme (M.TaqI) for binding to a duplex with a TT-mismatch, as shown by competitive fluorescence titrations. Altogether, our results demonstrate that macrocyclic distance-constrained bis-intercalators are efficient and selective mismatch-binding ligands that can interfere with mismatch-binding enzymes.
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Affiliation(s)
- Matthias Bahr
- Institute of Organic Chemistry, RWTH Aachen University, Landoltweg 1, D-52056 Aachen, Germany
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13
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Sanderson ML, Hassold TJ, Carrell DT. Proteins involved in meiotic recombination: a role in male infertility? Syst Biol Reprod Med 2008; 54:57-74. [PMID: 18446647 DOI: 10.1080/19396360701881922] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Meiotic recombination results in the formation of crossovers, by which genetic information is exchanged between homologous chromosomes during prophase I of meiosis. Recombination is a complex process involving many proteins. Alterations in the genes involved in recombination may result in infertility. Molecular studies have improved our understanding of the roles and mechanisms of the proteins and protein complexes involved in recombination, some of which have function in mitotic cells as well as meiotic cells. Human gene sequencing studies have been performed for some of these genes and have provided further information on the phenotypes observed in some infertile individuals. However, further studies are needed to help elucidate the particular role(s) of a given protein and to increase our understanding of these protein systems. This review will focus on our current understanding of proteins involved in meiotic recombination from a genomic perspective, summarizing our current understanding of known mutations and single nucleotide polymorphisms that may affect male fertility by altering meiotic recombination.
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Affiliation(s)
- Matthew L Sanderson
- Department of Surgery, University of Utah School of Medicine, Salt Lake City, Utah, USA
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14
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Lanzov VA. RecA homologous DNA transferase: Functional activities and a search for homology by recombining DNA molecules. Mol Biol 2007. [DOI: 10.1134/s0026893307030077] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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15
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Singleton SF, Roca AI, Lee AM, Xiao J. Probing the structure of RecA-DNA filaments. Advantages of a fluorescent guanine analog. Tetrahedron 2007; 63:3553-3566. [PMID: 17955055 PMCID: PMC2031864 DOI: 10.1016/j.tet.2006.10.092] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
The RecA protein of Escherichia coli plays a crucial roles in DNA recombination and repair, as well as various aspects of bacterial pathogenicity. The formation of a RecA-ATP-ssDNA complex initiates all RecA activities and yet a complete structural and mechanistic description of this filament has remained elusive. An analysis of RecA-DNA interactions was performed using fluorescently labeled oligonucleotides. A direct comparison was made between fluorescein and several fluorescent nucleosides. The fluorescent guanine analog 6-methylisoxanthopterin (6MI) demonstrated significant advantages over the other fluorophores and represents an important new tool for characterizing RecA-DNA interactions.
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Affiliation(s)
- Scott F. Singleton
- Division of Medicinal Chemistry & Natural Products, School of Pharmacy, The University of North Carolina at Chapel Hill, CB 7360, Chapel Hill, NC 27599-7360, USA
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16
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Egel R. RecA-DNA filament topology: the overlooked alternative of an unconventional syn-syn duplex intermediate. DNA Repair (Amst) 2007; 6:669-75. [PMID: 17317338 DOI: 10.1016/j.dnarep.2006.12.013] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2006] [Revised: 12/17/2006] [Accepted: 12/21/2006] [Indexed: 10/23/2022]
Abstract
The helical filaments of RecA protein mediate strand exchange for homologous recombination, but the paths of the interacting DNAs have yet to be determined. Although this interaction is commonly limited to three strands, it is reasoned here that the intrinsic symmetry relationships of quadruplex topology are superior in explaining a range of observations. In particular, this topology suggests the potential of post-exchange base pairing in the unorthodox configuration of syn-syn glycosidic bonds between the nucleotide bases and the pentose rings in the sugar-phosphate backbone, which would transiently be stabilized by the external scaffolding of the RecA protein filament.
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Affiliation(s)
- Richard Egel
- Institute of Molecular Biology and Physiology, University of Copenhagen, Ole Maaløe Vej 5, DK-2100 Copenhagen Ø, Denmark.
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