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Patrick Sung - One of the best experts on this subject based on the ideXlab platform.

  • interaction with rpa is necessary for rad52 repair center formation and for its mediator activity
    Journal of Biological Chemistry, 2008
    Co-Authors: Iben Plate, Patrick Sung, Swee Chuang Lim Hallwyl, Idina Shi, Lumir Krejci, Christian Muller, Line Albertsen, Uffe Hasbro Mortensen
    Abstract:

    Homologous recombination (HR) is a major DNA repair pathway and therefore essential for maintaining the integrity of the genome. HR is catalyzed by proteins encoded by genes of the RAD52 epistasis group, including the recombinase Rad51 and its mediator Rad52. HR proteins fused with green fluorescent protein form foci at damaged DNA reflecting the assembly of repair centers that harbor a high concentration of repair proteins. Rad52 mediates the recruitment of Rad51 and other HR proteins to DNA damage. To understand the mechanism for the assembly of Rad52-dependent DNA repair centers, we used a mutational strategy to identify a Rad52 domain essential for its recruitment to DNA repair foci. We present evidence to implicate an acidic domain in Rad52 in DNA repair focus formation. Mutations in this domain confer marked DNA damage sensitivity and recombination deficiency. Importantly, these Rad52 mutants are specifically compromised for interaction with the single-stranded DNA-binding factor RPA. Based on these findings, we propose a model where Rad52 displaces RPA from single-stranded DNA using the acidic domain as a molecular lever.

  • Effect of Amino Acid Substitutions in the Rad50 ATP Binding Domain on DNA Double Strand Break Repair in Yeast
    The Journal of biological chemistry, 2004
    Co-Authors: Ling Chen, Michael A. Resnick, Stephen Van Komen, Patrick Sung, Lumir Krejci, Kelly Trujillo, Dong Hyun Roh, L. Kevin Lewis, Alan E. Tomkinson
    Abstract:

    The Saccharomyces cerevisiae Rad50-Mre11-Xrs2 complex plays a central role in the cellular response to DNA double strand breaks. Rad50 has a globular ATPase head domain with a long coiled-coil tail. DNA binding by Rad50 is ATP-dependent and the Rad50-Mre11-Xrs2 complex possesses DNA unwinding and endonuclease activities that are regulated by ATP. Here we have examined the role of the Rad50 Walker type A ATP binding motif in DNA double strand break repair by a combination of genetic and biochemical approaches. Replacement of the conserved lysine residue within the Walker A motif with alanine, glutamate, or arginine results in the same DNA damage sensitivity and homologous recombination defect as the Rad50 deletion mutation. The Walker A mutations also cause a deficiency in non-homologous end-joining. As expected, complexes containing the Rad50 Walker A mutant proteins are defective in ATPase, ATP-dependent DNA unwinding, and ATP-stimulated endonuclease activities. Although the DNA end-bridging activity of the Rad50-Mre11-Xrs2 complex is ATP-independent, the end-bridging activity of complexes containing the Rad50 Walker A mutant proteins is salt-sensitive. These results provide a molecular explanation for the observed in vivo defects of the Rad50 Walker mutant strains and reveal a novel ATP-independent function for Rad50 in DNA end-bridging.

  • dna structure specific nuclease activities in the saccharomyces cerevisiae Rad50 mre11 complex
    Journal of Biological Chemistry, 2001
    Co-Authors: Kelly M. Trujillo, Patrick Sung
    Abstract:

    Saccharomyces cerevisiae Rad50 and MRE11 genes are required for the nucleolytic processing of DNA double-strand breaks. We have overexpressed Rad50 and Mre11 in yeast cells and purified them to near homogeneity. Consistent with the genetic data, we show that the purified Rad50 and Mre11 proteins form a stable complex. In the Rad50·Mre11 complex, the protein components exist in equimolar amounts. Mre11 has a 3′ to 5′ exonuclease activity that results in the release of mononucleotides. The addition of Rad50 does not significantly alter the exonucleolytic function of Mre11. Using homopolymeric oligonucleotide-based substrates, we show that the exonuclease activity of Mre11 and Rad50·Mre11 is enhanced for substrates with duplex DNA ends. We have examined the endonucleolytic function of Mre11 on defined, radiolabeled hairpin structures that also contain 3′ and 5′ single-stranded DNA overhangs. Mre11 is capable of cleaving hairpins and the 3′ single-stranded DNA tail. These endonuclease activities of Mre11 are enhanced markedly by Rad50 but only in the presence of ATP. Based on these results, we speculate that the Mre11 nuclease complex may mediate the nucleolytic digestion of the 5′ strand at secondary structures formed upon DNA strand separation.

  • DNA structure-specific nuclease activities in the Saccharomyces cerevisiae Rad50*Mre11 complex.
    The Journal of biological chemistry, 2001
    Co-Authors: Kelly M. Trujillo, Patrick Sung
    Abstract:

    Saccharomyces cerevisiae Rad50 and MRE11 genes are required for the nucleolytic processing of DNA double-strand breaks. We have overexpressed Rad50 and Mre11 in yeast cells and purified them to near homogeneity. Consistent with the genetic data, we show that the purified Rad50 and Mre11 proteins form a stable complex. In the Rad50·Mre11 complex, the protein components exist in equimolar amounts. Mre11 has a 3′ to 5′ exonuclease activity that results in the release of mononucleotides. The addition of Rad50 does not significantly alter the exonucleolytic function of Mre11. Using homopolymeric oligonucleotide-based substrates, we show that the exonuclease activity of Mre11 and Rad50·Mre11 is enhanced for substrates with duplex DNA ends. We have examined the endonucleolytic function of Mre11 on defined, radiolabeled hairpin structures that also contain 3′ and 5′ single-stranded DNA overhangs. Mre11 is capable of cleaving hairpins and the 3′ single-stranded DNA tail. These endonuclease activities of Mre11 are enhanced markedly by Rad50 but only in the presence of ATP. Based on these results, we speculate that the Mre11 nuclease complex may mediate the nucleolytic digestion of the 5′ strand at secondary structures formed upon DNA strand separation.

  • Superhelicity-driven homologous DNA pairing by yeast recombination factors Rad51 and Rad54.
    Molecular cell, 2000
    Co-Authors: Stephen Van Komen, Galina Petukhova, Stefan Sigurdsson, Sabrina Stratton, Patrick Sung
    Abstract:

    Yeast Rad51 recombinase has only minimal ability to form D loop. Addition of Rad54 renders D loop formation by Rad51 efficient, even when topologically relaxed DNA is used as substrate. Treatment of the nucleoprotein complex of Rad54 and relaxed DNA with topoisomerases reveals dynamic DNA remodeling to generate unconstrained negative and positive supercoils. DNA remodeling requires ATP hydrolysis by Rad54 and is stimulated by Rad51-DNA nucleoprotein complex. A marked sensitivity of DNA undergoing remodeling to P1 nuclease indicates that the negative supercoils produced lead to transient DNA strand separation. Thus, a specific interaction of Rad54 with the Rad51-ssDNA complex enhances the ability of the former to remodel DNA and allows the latter to harvest the negative supercoils generated for DNA joint formation.

Akira Shinohara - One of the best experts on this subject based on the ideXlab platform.

  • Rad50 zinc hook functions as a constitutive dimerization module interchangeable with SMC hinge.
    Nature communications, 2020
    Co-Authors: Hisashi Tatebe, Akira Shinohara, Chew Theng Lim, Hiroki Konno, Kazuhiro Shiozaki, Takayuki Uchihashi, Asako Furukohri
    Abstract:

    The human Mre11/Rad50 complex is one of the key factors in genome maintenance pathways. Previous nanoscale imaging by atomic force microscopy (AFM) showed that the ring-like structure of the human Mre11/Rad50 complex transiently opens at the zinc hook of Rad50. However, imaging of the human Mre11/Rad50 complex by high-speed AFM shows that the Rad50 coiled-coil arms are consistently bridged by the dimerized hooks while the Mre11/Rad50 ring opens by disconnecting the head domains; resembling other SMC proteins such as cohesin or condensin. These architectural features are conserved in the yeast and bacterial Mre11/Rad50 complexes. Yeast strains harboring the chimeric Mre11/Rad50 complex containing the SMC hinge of bacterial condensin MukB instead of the Rad50 hook properly functions in DNA repair. We propose that the basic role of the Rad50 hook is similar to that of the SMC hinge, which serves as rather stable dimerization interface.

  • Multiple pathways suppress non-allelic homologous recombination during meiosis in Saccharomyces cerevisiae.
    PLOS ONE, 2013
    Co-Authors: Miki Shinohara, Akira Shinohara
    Abstract:

    Recombination during meiosis in the form of crossover events promotes the segregation of homologous chromosomes by providing the only physical linkage between these chromosomes. Recombination occurs not only between allelic sites but also between non-allelic (ectopic) sites. Ectopic recombination is often suppressed to prevent non-productive linkages. In this study, we examined the effects of various mutations in genes involved in meiotic recombination on ectopic recombination during meiosis. RAD24, a DNA damage checkpoint clamp-loader gene, suppressed ectopic recombination in wild type in the same pathway as RAD51. In the absence of RAD24, a meiosis-specific recA homolog, DMC1, suppressed the recombination. Homology search and strand exchange in ectopic recombination occurred when either the RAD51 or the DMC1 recA homolog was absent, but was promoted by RAD52. Unexpectedly, the zip1 mutant, which is defective in chromosome synapsis, showed a decrease, rather than an increase, in ectopic recombination. Our results provide evidence for two types of ectopic recombination: one that occurs in wild-type cells and a second that occurs predominantly when the checkpoint pathway is inactivated.

  • rad52 associates with rpa and functions with rad55 and rad57 to assemble meiotic recombination complexes
    Genes & Development, 1998
    Co-Authors: Stephen L Gasior, Akira Shinohara, Anthony K Wong, Yoshiteru Kora, Douglas K Bishop
    Abstract:

    We show that the Saccharomyces cerevisiae recombination protein Rad52 and the single-strand DNA-binding protein RPA assemble into cytologically detectable subnuclear complexes (foci) during meiotic recombination. Immunostaining shows extensive colocalization of Rad52 and RPA and more limited colocalization of Rad52 with the strand exchange protein Rad51. Rad52 and RPA foci are distinct from those formed by Rad51, and its meiosis-specific relative Dmc1, in that they are also detected in meiosis during replication. In addition, RPA foci are observed during mitotic S phase. Double-strand breaks (DSBs) promote formation of RPA, Rad52, and Rad51 foci. Mutants that lack Spo11, a protein required for DSB formation, are defective in focus formation, and this defect is suppressed by ionizing radiation in a dose-dependent manner. DSBs are not sufficient for the appearance of Rad51 foci; Rad52, Rad55, and Rad57 are also required supporting a model in which these three proteins promote meiotic recombination by promoting the assembly of strand exchange complexes.

  • rad52 forms ring structures and co operates with rpa in single strand dna annealing
    Genes to Cells, 1998
    Co-Authors: Akira Shinohara, Miki Shinohara, Tsutomu Ohta, Shimako Matsuda, Tomoko Ogawa
    Abstract:

    Background The RAD52 epistasis group in Saccharomyces cerevisiae is involved in various types of homologous recombination including recombinational double-strand break (DSB) repair and meiotic recombination. A RecA homologue, Rad51, plays a pivotal role in homology search and strand exchange. Genetic analysis has shown that among members of its epistasis group, RAD52 alone is required for recombination between direct repeats yielding deletions. Very little has been discovered about the biochemical roles and structure of the Rad52 protein. Results Purified Rad52 protein binds to both single-stranded DNA (ssDNA) and double-stranded DNA (dsDNA). Electron microscope observations revealed that Rad52 molecules form multimeric rings. An increase in the intensity of fluorescence when Rad52 is bound to eDNA showed an alteration of the structure of ssDNA. RPA was binding to Rad52 and enhanced the annealing of complementary ssDNA molecules. This enhancement was not observed in Escherichia coli SSB protein or T4 phage gp32 protein. Conclusion Rad52 forms a ring-like structure and binds to ssDNA. Its structure and DNA binding properties are different from those of Rad51. The interaction of Rad52 with RPA plays an important role in the enhancement of annealing of complementary ssDNAs. We therefore propose that Rad52 mediates the RAD51-independent recombination through an ssDNA annealing, assisted by RPA.

John H J Petrini - One of the best experts on this subject based on the ideXlab platform.

  • The Rad50 hook domain regulates DNA damage signaling and tumorigenesis
    Genes & development, 2014
    Co-Authors: Ramon Roset, Akiko Inagaki, Marcel Hohl, Fabienne Brenet, Julien Lafrance-vanasse, Julian Lange, Joseph M. Scandura, John A. Tainer, Scott Keeney, John H J Petrini
    Abstract:

    The Mre11 complex (Mre11, Rad50, and Nbs1) is a central component of the DNA damage response (DDR), governing both double-strand break repair and DDR signaling. Rad50 contains a highly conserved Zn(2+)-dependent homodimerization interface, the Rad50 hook domain. Mutations that inactivate the hook domain produce a null phenotype. In this study, we analyzed mutants with reduced hook domain function in an effort to stratify hook-dependent Mre11 complex functions. One of these alleles, Rad50(46), conferred reduced Zn(2+) affinity and dimerization efficiency. Homozygous Rad50(46/46) mutations were lethal in mice. However, in the presence of wild-type Rad50, Rad50(46) exerted a dominant gain-of-function phenotype associated with chronic DDR signaling. At the organismal level, Rad50(+/46) exhibited hydrocephalus, liver tumorigenesis, and defects in primitive hematopoietic and gametogenic cells. These outcomes were dependent on ATM, as all phenotypes were mitigated in Rad50(+/46) Atm(+/-) mice. These data reveal that the murine Rad50 hook domain strongly influences Mre11 complex-dependent DDR signaling, tissue homeostasis, and tumorigenesis.

  • cohesin association to replication sites depends on Rad50 and promotes fork restart
    Molecular Cell, 2012
    Co-Authors: Philippe Pasero, John H J Petrini, Marcel Hohl, Mireille Tittelelmer, Armelle Lengronne, Marta Davidson, Julien Bacal, P Francois, Jennifer A Cobb
    Abstract:

    SUMMARY The cohesin complex holds together newly replicated chromatids and is involved in diverse pathways that preserve genome integrity. We show that in budding yeast, cohesin is transiently recruited to active replication origins, and it spreads along DNA as forks progress. When DNA synthesis is impeded, cohesin accumulates at replication sites and is critical for the recovery of stalled forks. Cohesin enrichment at replication forks does not depend on gH2A(X) formation, which differs from its loading requirements at DNA double-strand breaks (DSBs). However, cohesin localization is largely reduced in Rad50D mutants and in cells lacking both Mec1 and Tel1 checkpoint kinases. Interestingly, cohesin loading at replication sites depends on the structural features of Rad50 that are important for bridging sister chromatids, including the CXXC hook domain and the length of the coiled-coil extensions. Together, these data reveal a function for cohesin in the maintenance of genome integrity during S phase.

  • The Rad50 hook domain is a critical determinant of Mre11 complex functions.
    Nature structural & molecular biology, 2005
    Co-Authors: Jed J.w. Wiltzius, Marcel Hohl, James C Fleming, John H J Petrini
    Abstract:

    The Mre11 complex (in Saccharomyces cerevisiae: Mre11, Rad50 and Xrs2) influences multiple facets of chromosome break metabolism. A conserved feature of the Mre11 complex is a zinc-coordinating motif in Rad50 called the Rad50 hook. We established a diploid yeast strain, Rad50hook, in which Rad50 is encoded in halves, one from each of the two Rad50 alleles, with the residues constituting the hook deleted. In all respects, Rad50hook phenocopies complete Rad50 deficiency. Replacing the hook domain with a ligand-inducible FKBP dimerization cassette partially mitigated all phenotypes in a ligand-dependent manner. The data indicate that the Rad50 hook is critical for Mre11 complex–dependent DNA repair, telomere maintenance and meiotic double-strand break formation. Sister chromatid cohesion was unaffected by Rad50 deficiency, suggesting that molecular bridging required for recombinational DNA repair is qualitatively distinct from cohesin-mediated sister chromatid cohesion.

  • human Rad50 is physically associated with human mre11 identification of a conserved multiprotein complex implicated in recombinational dna repair
    Molecular and Cellular Biology, 1996
    Co-Authors: G M Dolganov, Richard S Maser, A Novikov, L Tosto, S Chong, Debra A Bressan, John H J Petrini
    Abstract:

    In this report, we describe the identification and molecular characterization of a human Rad50 homolog, hRad50. hRad50 was included in a collection of cDNAs which were isolated by a direct cDNA selection strategy focused on the chromosomal interval spanning 5q23 to 5q31. Alterations of the 5q23-q31 interval are frequently observed in myelodysplasia and myeloid leukemia. This strategy was thus undertaken to create a detailed genetic map of that region. Saccharomyces cerevisiae Rad50 (ScRad50) is one of three yeast RAD52 epistasis group members (ScRad50, ScMRE11, and ScXRS2) in which mutations eliminate meiotic recombination but confer a hyperrecombinational phenotype in mitotic cells. The yeast Rad50, Mre11, and Xrs2 proteins appear to act in a multiprotein complex, consistent with the observation that the corresponding mutants confer essentially identical phenotypes. In this report, we demonstrate that the human Rad50 and Mre11 proteins are stably associated in a protein complex which may include three other proteins. hRad50 is expressed in all tissues examined, but mRNA levels are significantly higher in the testis. Other human RAD52 epistasis group homologs exhibit this expression pattern, suggesting the involvement of human RAD52 epistasis group proteins in meiotic recombination. Human RAD52 epistasis group proteins are highly conserved and act in protein complexes that are analogous to those of their yeast counterparts. These findings indicate that the function of the RAD52 epistasis group is conserved in human cells.

Charles I. White - One of the best experts on this subject based on the ideXlab platform.

  • the arabidopsis homologue of xrcc3 plays an essential role in meiosis
    The EMBO Journal, 2004
    Co-Authors: Jeanyves Bleuyard, Charles I. White
    Abstract:

    The eukaryotic RecA homologue Rad51 is a key factor in homologous recombination and recombinational repair. Rad51-like proteins have been identified from yeast (Rad55, Rad57 and Dmc1) to vertebrates (Rad51B, Rad51C, Rad51D, Xrcc2, Xrcc3 and Dmc1). These Rad51-like proteins are all members of the genetic recombination and DNA damage repair pathways. The sequenced genome of Arabidopsis thaliana encodes putative homologues of all six vertebrate Rad51-like proteins. We have identified and characterized an Arabidopsis mutant defective for one of these, AtXRCC3, the homologue of XRCC3. atxrcc3 plants are sterile, while they have normal vegetative development. Cytological observation shows that the atxrcc3 mutation does not affect homologous chromosome synapsis, but leads to chromosome fragmentation after pachytene, thus disrupting both male and female gametogenesis. This study shows an essential role for AtXrcc3 in meiosis in plants and possibly in other higher eukaryotes. Furthermore, atxrcc3 cells and plants are hypersensitive to DNA-damaging treatments, supporting the involvement of this Arabidopsis Rad51-like protein in recombinational repair.

  • Rad50 function is essential for telomere maintenance in Arabidopsis
    Proceedings of the National Academy of Sciences of the United States of America, 2001
    Co-Authors: Maria Eugenia Gallego, Charles I. White
    Abstract:

    We have identified and characterized an Arabidopsis thaliana Rad50 mutant plant containing a T-DNA insertion in the AtRad50 gene and showing both meiotic and DNA repair defects. We report here that Rad50/Rad50 mutant cells show a progressive shortening of telomeric DNA relative to heterozygous Rad50/Rad50 controls and that the mutant cell population rapidly enters a crisis, with the majority of the cells dying. Surviving Rad50 mutant cells have longer telomeres than wild-type cells, indicating the existence in plants of an alternative Rad50-independent mechanism for telomere maintenance. These results report the role of a protein essential for double-strand break repair in telomere maintenance in higher eukaryotes.

  • Mutations in XRS2 and Rad50 delay but do not prevent mating-type switching in Saccharomyces cerevisiae.
    Molecular and cellular biology, 1994
    Co-Authors: E L Ivanov, Charles I. White, Neal Sugawara, F Fabre, James E. Haber
    Abstract:

    In Saccharomyces cerevisiae, a large number of genes in the RAD52 epistasis group has been implicated in the repair of chromosomal double-strand breaks and in both mitotic and meiotic homologous recombination. While most of these genes are essential for yeast mating-type (MAT) gene switching, neither Rad50 nor XRS2 is required to complete this specialized mitotic gene conversion process. Using a galactose-inducible HO endonuclease gene to initiate MAT switching, we have examined the effect of null mutations of Rad50 and of XRS2 on intermediate steps of this recombination event. Both Rad50 and xrs2 mutants exhibit a marked delay in the completion of switching. Both mutations reduce the extent of 5'-to-3' degradation from the end of the HO-created double-strand break. The steps of initial strand invasion and new DNA synthesis are delayed by approximately 30 min in mutant cells. However, later events are still further delayed, suggesting that XRS2 and Rad50 affect more than one step in the process. In the Rad50 xrs2 double mutant, the completion of MAT switching is delayed more than in either single mutant, without reducing the overall efficiency of the process. The XRS2 gene encodes an 854-amino-acid protein with no obvious similarity to the Rad50 protein or to any other protein in the database. Overexpression of Rad50 does not complement the defects in xrs2 or vice versa.

Miki Shinohara - One of the best experts on this subject based on the ideXlab platform.

  • rpa mediates recruitment of mrx to forks and double strand breaks to hold sister chromatids together
    Molecular Cell, 2016
    Co-Authors: Andrew Seeber, Anna Maria Hegnauer, Nicole Hustedt, Ishan Deshpande, Jerome Poli, Jan Eglinger, Philippe Pasero, Miki Shinohara
    Abstract:

    Summary The Mre11-Rad50-Xrs2 (MRX) complex is related to SMC complexes that form rings capable of holding two distinct DNA strands together. MRX functions at stalled replication forks and double-strand breaks (DSBs). A mutation in the N-terminal OB fold of the 70 kDa subunit of yeast replication protein A, rfa1-t11 , abrogates MRX recruitment to both types of DNA damage. The rfa1 mutation is functionally epistatic with loss of any of the MRX subunits for survival of replication fork stress or DSB recovery, although it does not compromise end-resection. High-resolution imaging shows that either the rfa1-t11 or the Rad50Δ mutation lets stalled replication forks collapse and allows the separation not only of opposing ends but of sister chromatids at breaks. Given that cohesin loss does not provoke visible sister separation as long as the RPA-MRX contacts are intact, we conclude that MRX also serves as a structural linchpin holding sister chromatids together at breaks.

  • Multiple pathways suppress non-allelic homologous recombination during meiosis in Saccharomyces cerevisiae.
    PLOS ONE, 2013
    Co-Authors: Miki Shinohara, Akira Shinohara
    Abstract:

    Recombination during meiosis in the form of crossover events promotes the segregation of homologous chromosomes by providing the only physical linkage between these chromosomes. Recombination occurs not only between allelic sites but also between non-allelic (ectopic) sites. Ectopic recombination is often suppressed to prevent non-productive linkages. In this study, we examined the effects of various mutations in genes involved in meiotic recombination on ectopic recombination during meiosis. RAD24, a DNA damage checkpoint clamp-loader gene, suppressed ectopic recombination in wild type in the same pathway as RAD51. In the absence of RAD24, a meiosis-specific recA homolog, DMC1, suppressed the recombination. Homology search and strand exchange in ectopic recombination occurred when either the RAD51 or the DMC1 recA homolog was absent, but was promoted by RAD52. Unexpectedly, the zip1 mutant, which is defective in chromosome synapsis, showed a decrease, rather than an increase, in ectopic recombination. Our results provide evidence for two types of ectopic recombination: one that occurs in wild-type cells and a second that occurs predominantly when the checkpoint pathway is inactivated.

  • rad52 forms ring structures and co operates with rpa in single strand dna annealing
    Genes to Cells, 1998
    Co-Authors: Akira Shinohara, Miki Shinohara, Tsutomu Ohta, Shimako Matsuda, Tomoko Ogawa
    Abstract:

    Background The RAD52 epistasis group in Saccharomyces cerevisiae is involved in various types of homologous recombination including recombinational double-strand break (DSB) repair and meiotic recombination. A RecA homologue, Rad51, plays a pivotal role in homology search and strand exchange. Genetic analysis has shown that among members of its epistasis group, RAD52 alone is required for recombination between direct repeats yielding deletions. Very little has been discovered about the biochemical roles and structure of the Rad52 protein. Results Purified Rad52 protein binds to both single-stranded DNA (ssDNA) and double-stranded DNA (dsDNA). Electron microscope observations revealed that Rad52 molecules form multimeric rings. An increase in the intensity of fluorescence when Rad52 is bound to eDNA showed an alteration of the structure of ssDNA. RPA was binding to Rad52 and enhanced the annealing of complementary ssDNA molecules. This enhancement was not observed in Escherichia coli SSB protein or T4 phage gp32 protein. Conclusion Rad52 forms a ring-like structure and binds to ssDNA. Its structure and DNA binding properties are different from those of Rad51. The interaction of Rad52 with RPA plays an important role in the enhancement of annealing of complementary ssDNAs. We therefore propose that Rad52 mediates the RAD51-independent recombination through an ssDNA annealing, assisted by RPA.