Rad51 Recombinase and Recombination Mediators (2003)

Through pairing and shuffling of related DNA sequences, homologous recombination (HR) 1The abbreviations used are: HR, homologous recombination; DSB, DNA double-stranded break; ssDNA, single-stranded DNA; dsDNA, double-stranded DNA; RPA, replication protein A. serves to create genetic diversity. In both mitotic and meiotic cells, HR is also an important mechanism for eliminating DNA double-stranded breaks (DSBs) (1Paques F. Haber J.E. Microbiol. Mol. Biol. Rev. 1999; 63: 349-404Crossref PubMed Google Scholar, 2Symington L.S. Microbiol. Mol. Biol. Rev. 2002; 66: 630-670Crossref PubMed Scopus (815) Google Scholar). Furthermore, HR is involved in restarting stalled DNA replication forks and provides a means for telomere length maintenance in cells lacking telomerase (3Cox M.M. Goodman M.F. Kreuzer K.N. Sherratt D.J. Sandler S.J. Marians K.J. Nature. 2000; 404: 37-41Crossref PubMed Scopus (871) Google Scholar, 4West S.C. Nat. Rev. Mol. Cell Biol. 2003; 4: 435-445Crossref PubMed Scopus (809) Google Scholar, 5Oakley T.J. Hickson I.D. DNA Repair (Amst.). 2002; 1: 175-207Crossref PubMed Scopus (45) Google Scholar, 6Michel B. Flores M.J. Viguera E. Grompone G. Seigneur M. Bidnenko V. Proc. Natl. Acad. Sci. U. S. A. 2001; 98: 8181-8188Crossref PubMed Scopus (250) Google Scholar). Accordingly, defects in HR result in sensitivity to genotoxic agents, mitotic and meiotic chromosome aberrations, and destabilization of the genome (7Kolodner R.D. Nature. 2000; 407: 687-689Crossref PubMed Scopus (14) Google Scholar, 8Richardson C. Jasin M. Cold Spring Harbor Symp. Quant. Biol. 2000; 65: 553-560Crossref PubMed Scopus (13) Google Scholar). Recent evidence points to a role of HR in cancer prevention via the tumor suppressors BRCA1 and BRCA2 (9Pierce A.J. Stark J.M. Araujo F.D. Moynahan M.E. Berwick M. Jasin M. Trends Cell Biol. 2001; 11: S52-S59Abstract Full Text PDF PubMed Scopus (235) Google Scholar). At the core of all HR reactions lies the ability of the recombination machinery to utilize a ssDNA molecule, derived from the processing of DSBs or stalled DNA replication forks (1Paques F. Haber J.E. Microbiol. Mol. Biol. Rev. 1999; 63: 349-404Crossref PubMed Google Scholar, 2Symington L.S. Microbiol. Mol. Biol. Rev. 2002; 66: 630-670Crossref PubMed Scopus (815) Google Scholar, 3Cox M.M. Goodman M.F. Kreuzer K.N. Sherratt D.J. Sandler S.J. Marians K.J. Nature. 2000; 404: 37-41Crossref PubMed Scopus (871) Google Scholar, 5Oakley T.J. Hickson I.D. DNA Repair (Amst.). 2002; 1: 175-207Crossref PubMed Scopus (45) Google Scholar, 6Michel B. Flores M.J. Viguera E. Grompone G. Seigneur M. Bidnenko V. Proc. Natl. Acad. Sci. U. S. A. 2001; 98: 8181-8188Crossref PubMed Scopus (250) Google Scholar, 10Krejci L. Chen L. Van Komen S. Sung P. Tomkinson A. Prog. Nucleic Acids Res. Mol. Biol. 2003; 74: 159-201Crossref PubMed Scopus (58) Google Scholar), to invade a homologous duplex. The product of this DNA strand invasion reaction is a structure called D-loop, and the overall enzymological process is referred to as homologous DNA pairing and strand exchange (Fig. 1) (10Krejci L. Chen L. Van Komen S. Sung P. Tomkinson A. Prog. Nucleic Acids Res. Mol. Biol. 2003; 74: 159-201Crossref PubMed Scopus (58) Google Scholar, 11Bianco P.R. Tracy R.B. Kowalczykowski S.C. Front Biosci. 1998; 3: 570-603Crossref PubMed Google Scholar). Resolution of the D-loop is accomplished by one of a number of pathways (1Paques F. Haber J.E. Microbiol. Mol. Biol. Rev. 1999; 63: 349-404Crossref PubMed Google Scholar, 2Symington L.S. Microbiol. Mol. Biol. Rev. 2002; 66: 630-670Crossref PubMed Scopus (815) Google Scholar) to yield recombinants that either entail a reciprocal exchange of genetic information flanking the initiation site (crossover recombinants) or not (non-crossover recombinants). The homologous DNA pairing and strand exchange reaction is mediated by a class of conserved recombinase enzymes: UvsX in bacteriophage T4, RecA in Escherichia coli, and Rad51 in eukaryotes (11Bianco P.R. Tracy R.B. Kowalczykowski S.C. Front Biosci. 1998; 3: 570-603Crossref PubMed Google Scholar, 12Bleuit J.S. Xu H. Ma Y. Wang T. Liu J. Morrical S.W. Proc. Natl. Acad. Sci. U. S. A. 2001; 98: 8298-8305Crossref PubMed Scopus (68) Google Scholar). Studies conducted in the past several years have helped define a set of operational principles for the Rad51 recombinase and have unveiled an array of ancillary factors of Rad51. Genetic analyses of DNA double-stranded break repair and mitotic and meiotic recombination in the budding yeast Saccharomyces cerevisiae have led to the identification of genes collectively known as the RAD52 epistasis group (1Paques F. Haber J.E. Microbiol. Mol. Biol. Rev. 1999; 63: 349-404Crossref PubMed Google Scholar, 2Symington L.S. Microbiol. Mol. Biol. Rev. 2002; 66: 630-670Crossref PubMed Scopus (815) Google Scholar). Among the members of the RAD52 group, RAD51 is, arguably, the most famed. The RAD51-encoded product has structural homology to E. coli RecA and T4 UvsX proteins and is highly conserved among eukaryotes (10Krejci L. Chen L. Van Komen S. Sung P. Tomkinson A. Prog. Nucleic Acids Res. Mol. Biol. 2003; 74: 159-201Crossref PubMed Scopus (58) Google Scholar, 11Bianco P.R. Tracy R.B. Kowalczykowski S.C. Front Biosci. 1998; 3: 570-603Crossref PubMed Google Scholar, 13Story R.M. Bishop D.K. Kleckner N. Steitz T.A. Science. 1993; 259: 1892-1896Crossref PubMed Scopus (145) Google Scholar). In many respects, Rad51 behaves like RecA in homologous DNA pairing and strand exchange. The recombinase activity of Rad51 can be described in three kinetic phases. The Presynaptic Phase—Like RecA, Rad51 forms a right-handed helical filament on ssDNA in which the DNA is held in an extended state (10Krejci L. Chen L. Van Komen S. Sung P. Tomkinson A. Prog. Nucleic Acids Res. Mol. Biol. 2003; 74: 159-201Crossref PubMed Scopus (58) Google Scholar, 11Bianco P.R. Tracy R.B. Kowalczykowski S.C. Front Biosci. 1998; 3: 570-603Crossref PubMed Google Scholar, 14Yu X. Jacobs S.A. West S.C. Ogawa T. Egelman E.H. Proc. Natl. Acad. Sci. U. S. A. 2001; 98: 8419-8424Crossref PubMed Scopus (205) Google Scholar). The Rad51-ssDNA nucleoprotein filament, often referred to as the presynaptic filament, contains a binding site for dsDNA. The initiating ssDNA substrate is bound within the "primary" site of the presynaptic filament, and the homologous duplex resides within the "secondary" site (10Krejci L. Chen L. Van Komen S. Sung P. Tomkinson A. Prog. Nucleic Acids Res. Mol. Biol. 2003; 74: 159-201Crossref PubMed Scopus (58) Google Scholar, 11Bianco P.R. Tracy R.B. Kowalczykowski S.C. Front Biosci. 1998; 3: 570-603Crossref PubMed Google Scholar). The capability to hold two DNA molecules in close proximity underlies the ability of the presynaptic filament to form DNA joints between these molecules. Interestingly, even though Rad51 hydrolyzes ATP (15Sung P. Science. 1994; 265: 1241-1243Crossref PubMed Scopus (754) Google Scholar), presynaptic filament assembly requires only ATP binding (2Symington L.S. Microbiol. Mol. Biol. Rev. 2002; 66: 630-670Crossref PubMed Scopus (815) Google Scholar, 10Krejci L. Chen L. Van Komen S. Sung P. Tomkinson A. Prog. Nucleic Acids Res. Mol. Biol. 2003; 74: 159-201Crossref PubMed Scopus (58) Google Scholar, 11Bianco P.R. Tracy R.B. Kowalczykowski S.C. Front Biosci. 1998; 3: 570-603Crossref PubMed Google Scholar, 16Sung P. Stratton S.A. J. Biol. Chem. 1996; 271: 27983-27986Abstract Full Text Full Text PDF PubMed Scopus (149) Google Scholar). Rad51 nucleates onto ssDNA rather slowly, thus rendering presynaptic filament assembly vulnerable to competing factors. In fact, replication protein A (RPA), a classical ssDNA-binding protein, while playing an important role in Rad51-mediated recombination, also paradoxically competes with Rad51 for binding sites on the initiating ssDNA substrate. A number of accessory proteins, termed recombination mediators (10Krejci L. Chen L. Van Komen S. Sung P. Tomkinson A. Prog. Nucleic Acids Res. Mol. Biol. 2003; 74: 159-201Crossref PubMed Scopus (58) Google Scholar, 12Bleuit J.S. Xu H. Ma Y. Wang T. Liu J. Morrical S.W. Proc. Natl. Acad. Sci. U. S. A. 2001; 98: 8298-8305Crossref PubMed Scopus (68) Google Scholar) (see below), promote the nucleation of Rad51 onto ssDNA and in doing so help Rad51 overcome the inhibitory effect of RPA (Fig. 2) (2Symington L.S. Microbiol. Mol. Biol. Rev. 2002; 66: 630-670Crossref PubMed Scopus (815) Google Scholar, 10Krejci L. Chen L. Van Komen S. Sung P. Tomkinson A. Prog. Nucleic Acids Res. Mol. Biol. 2003; 74: 159-201Crossref PubMed Scopus (58) Google Scholar, 12Bleuit J.S. Xu H. Ma Y. Wang T. Liu J. Morrical S.W. Proc. Natl. Acad. Sci. U. S. A. 2001; 98: 8298-8305Crossref PubMed Scopus (68) Google Scholar). The Synaptic Phase—Herein, the incoming duplex is incorporated into the presynaptic filament through multiple contact points and then sampled for homology. Extensive studies with RecA have yielded no evidence for progressive scanning of the duplex in homology search. Rather, to test for homology, the incoming duplex is held transiently within the secondary binding site of the RecA presynaptic filament, and if homology is not found, the duplex is released. This cycle of binding and release of the duplex goes on until homology is located. Given its structural and functional similarities to RecA, it seems reasonable to assume that the Rad51 presynaptic filament also employs the same random collision mode of homology search (10Krejci L. Chen L. Van Komen S. Sung P. Tomkinson A. Prog. Nucleic Acids Res. Mol. Biol. 2003; 74: 159-201Crossref PubMed Scopus (58) Google Scholar, 11Bianco P.R. Tracy R.B. Kowalczykowski S.C. Front Biosci. 1998; 3: 570-603Crossref PubMed Google Scholar). However, Rad54 may endow the presynaptic filament with the ability to scan the incoming duplex molecule for homology (10Krejci L. Chen L. Van Komen S. Sung P. Tomkinson A. Prog. Nucleic Acids Res. Mol. Biol. 2003; 74: 159-201Crossref PubMed Scopus (58) Google Scholar, 17Ristic D. Wyman C. Paulusma C. Kanaar R. Proc. Natl. Acad. Sci. U. S. A. 2001; 98: 8454-8460Crossref PubMed Scopus (110) Google Scholar, 18Van Komen S. Petukhova G. Sigurdsson S. Stratton S. Sung P. Mol. Cell. 2000; 6: 563-572Abstract Full Text Full Text PDF PubMed Scopus (190) Google Scholar) (see "Rad54, a DNA Translocase and Supercoiling Motor"). Once homology is located, the initial capture of the duplex and its alignment with the ssDNA molecule are facilitated through DNA joints that are "paranemic" in nature. The paranemic joints, which occur away from a free DNA end, involve canonical Watson-Crick hydrogen bonding. The efficiency of paranemic joint formation is dictated by the ease of DNA strand breathing (10Krejci L. Chen L. Van Komen S. Sung P. Tomkinson A. Prog. Nucleic Acids Res. Mol. Biol. 2003; 74: 159-201Crossref PubMed Scopus (58) Google Scholar, 11Bianco P.R. Tracy R.B. Kowalczykowski S.C. Front Biosci. 1998; 3: 570-603Crossref PubMed Google Scholar, 19Gupta R.C. Folta-Stogniew E. O'Malley S. Takahashi M. Radding C.M. Mol. Cell. 1999; 4: 705-714Abstract Full Text Full Text PDF PubMed Scopus (72) Google Scholar). Thus, the higher the AT base pair content of the duplex, the greater the propensity for it to form paranemic joints with its ssDNA partner (19Gupta R.C. Folta-Stogniew E. O'Malley S. Takahashi M. Radding C.M. Mol. Cell. 1999; 4: 705-714Abstract Full Text Full Text PDF PubMed Scopus (72) Google Scholar). However, Rad54, which transiently denatures DNA base pairs (10Krejci L. Chen L. Van Komen S. Sung P. Tomkinson A. Prog. Nucleic Acids Res. Mol. Biol. 2003; 74: 159-201Crossref PubMed Scopus (58) Google Scholar, 18Van Komen S. Petukhova G. Sigurdsson S. Stratton S. Sung P. Mol. Cell. 2000; 6: 563-572Abstract Full Text Full Text PDF PubMed Scopus (190) Google Scholar), could promote paranemic joint formation with DNA substrates that have a high GC content. Although the paranemic linkage brings the two recombining molecules into homologous registry, it is transient (10Krejci L. Chen L. Van Komen S. Sung P. Tomkinson A. Prog. Nucleic Acids Res. Mol. Biol. 2003; 74: 159-201Crossref PubMed Scopus (58) Google Scholar, 11Bianco P.R. Tracy R.B. Kowalczykowski S.C. Front Biosci. 1998; 3: 570-603Crossref PubMed Google Scholar, 19Gupta R.C. Folta-Stogniew E. O'Malley S. Takahashi M. Radding C.M. Mol. Cell. 1999; 4: 705-714Abstract Full Text Full Text PDF PubMed Scopus (72) Google Scholar). The more enduring plectonemic joint is formed when a free DNA end is encountered, which in the cellular setting is likely to be present in the initiating ssDNA substrate (Fig. 1). The two DNA strands in the plectonemic linkage are bound by Watson-Crick hydrogen bonds and are intertwined topologically (10Krejci L. Chen L. Van Komen S. Sung P. Tomkinson A. Prog. Nucleic Acids Res. Mol. Biol. 2003; 74: 159-201Crossref PubMed Scopus (58) Google Scholar, 11Bianco P.R. Tracy R.B. Kowalczykowski S.C. Front Biosci. 1998; 3: 570-603Crossref PubMed Google Scholar). The Postsynaptic Phase—Herein, the complementary strand in the duplex molecule is continually taken up into the presynaptic filament to base pair with the initiating ssDNA; the net result is the extension of the initial plectonemic DNA joint. This process is referred to as "DNA strand exchange" or "DNA branch migration." The extent of DNA branch migration is determined by the length of the presynaptic filament. A stimulatory effect of Rad54 on the branch migration reaction has been noted (20Solinger J.A. Heyer W.D. Proc. Natl. Acad. Sci. U. S. A. 2001; 98: 8447-8453Crossref PubMed Scopus (78) Google Scholar) (see below). RPA—Through its ability to protect and help remove secondary structure in ssDNA, RPA plays a key role in DNA metabolic pathways that entail the formation of a ssDNA intermediate. The involvement of RPA in recombination is multifaceted. It has both positive and negative effects on the recombination reaction. The stimulatory effect of RPA is seen most clearly when long DNA substrates are used (10Krejci L. Chen L. Van Komen S. Sung P. Tomkinson A. Prog. Nucleic Acids Res. Mol. Biol. 2003; 74: 159-201Crossref PubMed Scopus (58) Google Scholar, 11Bianco P.R. Tracy R.B. Kowalczykowski S.C. Front Biosci. 1998; 3: 570-603Crossref PubMed Google Scholar), whereas only a modest stimulatory effect of RPA is noted when oligonucleotides are employed as substrates (21Krejci L. Van Komen S. Li Y. Villemain J. Reddy M.S. Klein H. Ellenberger T. Sung P. Nature. 2003; 423: 305-309Crossref PubMed Scopus (503) Google Scholar). RPA promotes Rad51 presynaptic filament assembly by minimizing secondary structure in long ssDNA molecules (10Krejci L. Chen L. Van Komen S. Sung P. Tomkinson A. Prog. Nucleic Acids Res. Mol. Biol. 2003; 74: 159-201Crossref PubMed Scopus (58) Google Scholar, 11Bianco P.R. Tracy R.B. Kowalczykowski S.C. Front Biosci. 1998; 3: 570-603Crossref PubMed Google Scholar). In addition, by sequestering free ssDNA, RPA renders the already made DNA joints less prone to a reversal reaction (22Eggler A.L. Inman R.B. Cox M.M. J. Biol. Chem. 2002; 277: 39280-39288Abstract Full Text Full Text PDF PubMed Scopus (66) Google Scholar). RPA also prevents ssDNA from precluding the entry of duplex DNA into the secondary binding site of the Rad51 presynaptic filament (23Van Komen S. Petukhova G. Sigurdsson S. Sung P. J. Biol. Chem. 2002; 277: 43578-43587Abstract Full Text Full Text PDF PubMed Scopus (54) Google Scholar). Because of the high affinity of RPA for ssDNA, when an excess of RPA is added either with or prior to Rad51 to the ssDNA, assembly of the presynaptic filament is hindered (2Symington L.S. Microbiol. Mol. Biol. Rev. 2002; 66: 630-670Crossref PubMed Scopus (815) Google Scholar, 10Krejci L. Chen L. Van Komen S. Sung P. Tomkinson A. Prog. Nucleic Acids Res. Mol. Biol. 2003; 74: 159-201Crossref PubMed Scopus (58) Google Scholar, 24Sung P. Genes Dev. 1997; 11: 1111-1121Crossref PubMed Scopus (461) Google Scholar, 25Sugiyama T. Zaitseva E.M. Kowalczykowski S.C. J. Biol. Chem. 1997; 272: 7940-7945Abstract Full Text Full Text PDF PubMed Scopus (263) Google Scholar). This paradoxical behavior of RPA has been used as the basis for uncovering recombination mediators (Fig. 2) (2Symington L.S. Microbiol. Mol. Biol. Rev. 2002; 66: 630-670Crossref PubMed Scopus (815) Google Scholar, 10Krejci L. Chen L. Van Komen S. Sung P. Tomkinson A. Prog. Nucleic Acids Res. Mol. Biol. 2003; 74: 159-201Crossref PubMed Scopus (58) Google Scholar). Rad52 and Its Recombination Mediator Function—In S. cerevisiae, the suppression of Rad51 presynaptic filament assembly by RPA is overcome by Rad52. That Rad52 has recombination mediator activity is fully corroborated by cytological data (26Lisby M. Rothstein R. Mortensen U.H. Proc. Natl. Acad. Sci. U. S. A. 2001; 98: 8276-8282Crossref PubMed Scopus (350) Google Scholar, 27Gasior S.L. Wong A.K. Kora Y. Shinohara A. Bishop D.K. Genes Dev. 1998; 12: 2208-2221Crossref PubMed Scopus Google Scholar) and by that the of Rad51 to a N. Wang X. Haber J.E. Mol. Cell. 2003; 12: Full Text Full Text PDF PubMed Scopus Google Scholar, B. Komen S. Sung P. Mol. Cell. 2003; 12: Full Text Full Text PDF PubMed Scopus Google Scholar). Rad52 is and a molecule A. Shinohara M. T. S. Ogawa T. Genes 1998; 3: PubMed Scopus Google Scholar). The of the Rad52 structure on from in the protein with a E. A. S. A. Van E. West S.C. Egelman E.H. Biol. 2000; Full Text Full Text PDF PubMed Scopus Google Scholar). The evidence points to ssDNA bound on the of the Rad52 Liu Y. West S.C. Proc. Natl. Acad. Sci. U. S. A. 2002; PubMed Scopus Google Scholar, H. R. S. T. S. Mol. Cell. 2002; Full Text Full Text PDF PubMed Scopus Google Scholar). The of Rad52 likely it with the ability to DNA and a nucleoprotein S. cerevisiae Rad51 and Rad52 in the yeast and form a formation between Rad51 and Rad52 is for the recombination mediator activity of the (2Symington L.S. Microbiol. Mol. Biol. Rev. 2002; 66: 630-670Crossref PubMed Scopus (815) Google Scholar, 10Krejci L. Chen L. Van Komen S. Sung P. Tomkinson A. Prog. Nucleic Acids Res. Mol. Biol. 2003; 74: 159-201Crossref PubMed Scopus (58) Google Scholar, L. B. Rothstein R. Mortensen U.H. Sung P. J. Biol. Chem. 2002; 277: Full Text Full Text PDF PubMed Scopus Google Scholar). Rad52 ssDNA has affinity for (10Krejci L. Chen L. Van Komen S. Sung P. Tomkinson A. Prog. Nucleic Acids Res. Mol. Biol. 2003; 74: 159-201Crossref PubMed Scopus (58) Google Scholar, U.H. C. Rothstein R. Proc. Natl. Acad. Sci. U. S. A. 1996; PubMed Scopus Google Scholar). Recent data on the DNA of Rad52 an structure that a on the This is with and Liu Y. West S.C. Proc. Natl. Acad. Sci. U. S. A. 2002; PubMed Scopus Google Scholar, H. R. S. T. S. Mol. Cell. 2002; Full Text Full Text PDF PubMed Scopus Google Scholar) that are involved in binding DNA H. R. S. T. S. Mol. Cell. 2002; Full Text Full Text PDF PubMed Scopus Google Scholar). data that binding of the to ssDNA provides nucleation sites for the of free Rad51 molecules to the presynaptic filament (10Krejci L. Chen L. Van Komen S. Sung P. Tomkinson A. Prog. Nucleic Acids Res. Mol. Biol. 2003; 74: 159-201Crossref PubMed Scopus (58) Google Scholar, T. Kowalczykowski S.C. J. Biol. Chem. 2002; 277: Full Text Full Text PDF PubMed Scopus Google Scholar, B. Sung P. J. Biol. Chem. 2000; Full Text Full Text PDF PubMed Scopus Google Scholar). Rad52 also This of Rad52 is to the to to ssDNA with RPA T. Kowalczykowski S.C. J. Biol. Chem. 2002; 277: Full Text Full Text PDF PubMed Scopus Google Scholar). to the structure of Rad52 and the is to to multiple with ssDNA, likely to be for the and of these protein with the Furthermore, it is that the of these protein that a nucleation to the of multiple Rad51 molecules onto ssDNA for a Rad51 filament. It is important to that in S. cerevisiae, Rad52 is also for a of recombination and DNA repair that occur when Rad51 is which could often a more that of (1Paques F. Haber J.E. Microbiol. Mol. Biol. Rev. 1999; 63: 349-404Crossref PubMed Google Scholar, 2Symington L.S. Microbiol. Mol. Biol. Rev. 2002; 66: 630-670Crossref PubMed Scopus (815) Google Scholar). and Rad51 and proteins homology to Rad51 and are as of Rad51. two proteins form a (2Symington L.S. Microbiol. Mol. Biol. Rev. 2002; 66: 630-670Crossref PubMed Scopus (815) Google Scholar, 10Krejci L. Chen L. Van Komen S. Sung P. Tomkinson A. Prog. Nucleic Acids Res. Mol. Biol. 2003; 74: 159-201Crossref PubMed Scopus (58) Google Scholar). ssDNA and a recombination mediator activity P. Genes Dev. 1997; 11: 1111-1121Crossref PubMed Scopus (461) Google Scholar). In with the the of Rad51 to DSBs is in and as by cytological and N. Wang X. Haber J.E. Mol. Cell. 2003; 12: Full Text Full Text PDF PubMed Scopus Google Scholar, B. Komen S. Sung P. Mol. Cell. 2003; 12: Full Text Full Text PDF PubMed Scopus Google Scholar, S.L. H. U. R. Bishop D.K. Proc. Natl. Acad. Sci. U. S. A. 2001; 98: PubMed Scopus Google Scholar). between and Rad51 is seen in the yeast (2Symington L.S. Microbiol. Mol. Biol. Rev. 2002; 66: 630-670Crossref PubMed Scopus (815) Google Scholar), and Rad51 P. Genes Dev. 1997; 11: 1111-1121Crossref PubMed Scopus (461) Google Scholar). A that also the presynaptic filament L.S. J. 2002; PubMed Scopus Google Scholar). Rad51 and are in proteins among to form three and that have ssDNA binding activity (2Symington L.S. Microbiol. Mol. Biol. Rev. 2002; 66: 630-670Crossref PubMed Scopus (815) Google Scholar). In addition, and can form a (2Symington L.S. Microbiol. Mol. Biol. Rev. 2002; 66: 630-670Crossref PubMed Scopus (815) Google Scholar). The from a number of cytological and genetic are with these pairs as mediators of Rad51 presynaptic filament assembly (2Symington L.S. Microbiol. Mol. Biol. Rev. 2002; 66: 630-670Crossref PubMed Scopus (815) Google Scholar, 4West S.C. Nat. Rev. Mol. Cell Biol. 2003; 4: 435-445Crossref PubMed Scopus (809) Google Scholar, M. M.S. S. T. E. D. S. Mol. Cell. Biol. 2001; PubMed Scopus (461) Google Scholar). evidence that a role has been S. Van Komen S. D. J.S. Sung P. Genes Dev. 2001; PubMed Scopus Google Scholar). It is that and also have a recombination mediator activity and with the in the of Rad51 to recombination Presynaptic of Rad54 studies have S. cerevisiae Rad54 in the assembly and of the presynaptic filament B. Komen S. Sung P. Mol. Cell. 2003; 12: Full Text Full Text PDF PubMed Scopus Google Scholar, Kowalczykowski S.C. J. Biol. Chem. 2003; Full Text Full Text PDF PubMed Scopus Google Scholar). The presynaptic of Rad54 is with the that the of Rad51 to is in meiotic S. cerevisiae cells lacking Rad54 M. S.L. Bishop D.K. Shinohara A. Proc. Natl. Acad. Sci. U. S. A. 2000; PubMed Scopus Google Scholar). in cells for Rad54, the of DNA Rad51 is J. E. J. Kanaar R. Biol. 1999; Full Text Full Text PDF PubMed Scopus Google Scholar). a in Rad51 to a has been by in the S. cerevisiae B. Komen S. Sung P. Mol. Cell. 2003; 12: Full Text Full Text PDF PubMed Scopus Google Scholar). Because Rad54 Rad51 and ssDNA (10Krejci L. Chen L. Van Komen S. Sung P. Tomkinson A. Prog. Nucleic Acids Res. Mol. Biol. 2003; 74: 159-201Crossref PubMed Scopus (58) Google Scholar, B. Komen S. Sung P. Mol. Cell. 2003; 12: Full Text Full Text PDF PubMed Scopus Google Scholar), Rad54 Rad51 onto ssDNA to presynaptic filament a Recombination with Rad51 through its and via several of a conserved called the S.C. Nat. Rev. Mol. Cell Biol. 2003; 4: 435-445Crossref PubMed Scopus (809) Google Scholar, L. T. S. M. Nature. 2002; PubMed Scopus Google Scholar, S.C. Nat. Biol. 2002; PubMed Scopus Google Scholar). Recent and studies have an ability of BRCA2 to ssDNA via three DNA binding that are present in many proteins H. J. E. Y. N. Chen Science. 2002; PubMed Scopus Google Scholar). It has been that BRCA2 as a recombination mediator in S.C. Nat. Biol. 2002; PubMed Scopus Google Scholar, H. J. E. Y. N. Chen Science. 2002; PubMed Scopus Google Scholar). a role the recombination of BRCA2 cells and the ability of these cells to DNA Rad51 S.C. Nat. Rev. Mol. Cell Biol. 2003; 4: 435-445Crossref PubMed Scopus (809) Google Scholar). the of multiple Rad51 binding in BRCA2 could that a number of Rad51 molecules are by BRCA2 to ssDNA to the assembly of the presynaptic filament. Rad54, a DNA Translocase and Supercoiling Rad51 has only a modest ability to a D-loop, of a of Rad54 renders D-loop formation highly (2Symington L.S. Microbiol. Mol. Biol. Rev. 2002; 66: 630-670Crossref PubMed Scopus (815) Google Scholar, 10Krejci L. Chen L. Van Komen S. Sung P. Tomkinson A. Prog. Nucleic Acids Res. Mol. Biol. 2003; 74: 159-201Crossref PubMed Scopus (58) Google Scholar, G. Stratton S. Sung P. Nature. 1998; PubMed Scopus Google Scholar). Rad54, a of the protein has a that is on for The free from ATP the of Rad54 on duplex which positive of protein and negative it (Fig. (10Krejci L. Chen L. Van Komen S. Sung P. Tomkinson A. Prog. Nucleic Acids Res. Mol. Biol. 2003; 74: 159-201Crossref PubMed Scopus (58) Google Scholar, 17Ristic D. Wyman C. Paulusma C. Kanaar R. Proc. Natl. Acad. Sci. U. S. A. 2001; 98: 8454-8460Crossref PubMed Scopus (110) Google Scholar, 18Van Komen S. Petukhova G. Sigurdsson S. Stratton S. Sung P. Mol. Cell. 2000; 6: 563-572Abstract Full Text Full Text PDF PubMed Scopus (190) Google Scholar). The negative by Rad54 to transient of the DNA strands Komen S. Petukhova G. Sigurdsson S. Stratton S. Sung P. Mol. Cell. 2000; 6: 563-572Abstract Full Text Full Text PDF PubMed Scopus (190) Google Scholar). that the activity of Rad54 the DNA and and recombination (2Symington L.S. Microbiol. Mol. Biol. Rev. 2002; 66: 630-670Crossref PubMed Scopus (815) Google Scholar, 10Krejci L. Chen L. Van Komen S. Sung P. Tomkinson A. Prog. Nucleic Acids Res. Mol. Biol. 2003; 74: 159-201Crossref PubMed Scopus (58) Google Scholar). The and DNA of Rad54 are by Rad51 (2Symington L.S. Microbiol. Mol. Biol. Rev. 2002; 66: 630-670Crossref PubMed Scopus (815) Google Scholar, 10Krejci L. Chen L. Van Komen S. Sung P. Tomkinson A. Prog. Nucleic Acids Res. Mol. Biol. 2003; 74: 159-201Crossref PubMed Scopus (58) Google Scholar). Although the Rad51 presynaptic filament likely a random collision mechanism to search for homology in the incoming duplex molecule, Rad54 may endow the presynaptic filament with the ability to scan the duplex for homology. The negative by Rad54 both paranemic and plectonemic DNA joint formation (Fig. from the homologous pairing Rad54 also the of DNA branch migration (20Solinger J.A. Heyer W.D. Proc. Natl. Acad. Sci. U. S. A. 2001; 98: 8447-8453Crossref PubMed Scopus (78) Google Scholar). on duplex Rad54 bound Rad51 from its This of Rad54 may be for Rad51 from made DNA joints, the of Rad51 and DNA branch migration J.A. Heyer W.D. Mol. Cell. 2002; Full Text Full Text PDF PubMed Scopus Google Scholar). and protein has been described in S. cerevisiae and (10Krejci L. Chen L. Van Komen S. Sung P. Tomkinson A. Prog. Nucleic Acids Res. Mol. Biol. 2003; 74: 159-201Crossref PubMed Scopus (58) Google Scholar). has a that its on duplex DNA to in the like In addition, Rad51 and the Rad51-mediated D-loop reaction (2Symington L.S. Microbiol. Mol. Biol. Rev. 2002; 66: 630-670Crossref PubMed Scopus (815) Google Scholar, 10Krejci L. Chen L. Van Komen S. Sung P. Tomkinson A. Prog. Nucleic Acids Res. Mol. Biol. 2003; 74: 159-201Crossref PubMed Scopus (58) Google Scholar, G. Sung P. Klein H. Genes Dev. 2000; PubMed Scopus Google Scholar). can promote DNA branch migration and Rad51 from duplex DNA is not a of mitotic recombination and has a on meiotic recombination (2Symington L.S. Microbiol. Mol. Biol. Rev. 2002; 66: 630-670Crossref PubMed Scopus (815) Google Scholar, M. Shinohara A. Bishop D.K. 2003; Google Scholar). a activity T. H. Nucleic Acids Res. 2002; PubMed Scopus Google Scholar) by Rad54 number of members are involved in and DNA repair C.M. G. 2002; 3: PubMed Scopus Google Scholar). this several have Rad54, a canonical of the protein also has a In these that A. A. Kowalczykowski S.C. Nat. Biol. 2003; PubMed Scopus Google Scholar) and the of DNA into to M. Van Komen S. J.E. Sung P. J. Biol. Chem. 2003; Full Text Full Text PDF PubMed Scopus Google Scholar, V. Genes Dev. 2002; PubMed Scopus Google Scholar), it that Rad54 from S. cerevisiae and the ability to A. A. Kowalczykowski S.C. Nat. Biol. 2003; PubMed Scopus Google Scholar, M. Van Komen S. J.E. Sung P. J. Biol. Chem. 2003; Full Text Full Text PDF PubMed Scopus Google Scholar, V. Genes Dev. 2002; PubMed Scopus Google Scholar). Furthermore, S. cerevisiae Rad54 M. Van Komen S. J.E. Sung P. J. Biol. Chem. 2003; Full Text Full Text PDF PubMed Scopus Google Scholar). The of Rad54 is by Rad51 and requires ATP by Rad54 A. A. Kowalczykowski S.C. Nat. Biol. 2003; PubMed Scopus Google Scholar, M. Van Komen S. J.E. Sung P. J. Biol. Chem. 2003; Full Text Full Text PDF PubMed Scopus Google Scholar, V. Genes Dev. 2002; PubMed Scopus Google Scholar). In two of the Rad54 with the Rad51 presynaptic filament in D-loop reactions duplex In fact, a more D-loop reaction seen when a to the that the recombination factors have to with M. Van Komen S. J.E. Sung P. J. Biol. Chem. 2003; Full Text Full Text PDF PubMed Scopus Google Scholar, V. Genes Dev. 2002; PubMed Scopus Google Scholar). The ability of Rad54 to is likely to its DNA and M. Van Komen S. J.E. Sung P. J. Biol. Chem. 2003; Full Text Full Text PDF PubMed Scopus Google Scholar), as has been for the from yeast and A. M. R. T. Cell. 2000; Full Text Full Text PDF PubMed Scopus Google Scholar). HR are highly and to multiple of Studies in the past years have helped define the of many core recombination factors. However, several In the functional among the recombination or in a to be The in which BRCA1 HR efficiency is not Genetic analyses have that HR is to and negative by a number of DNA T.J. Hickson I.D. DNA Repair (Amst.). 2002; 1: 175-207Crossref PubMed Scopus (45) Google Scholar, M. Nature. 2003; 423: PubMed Scopus Google Scholar), and studies are to the HR of these (21Krejci L. Van Komen S. Li Y. Villemain J. Reddy M.S. Klein H. Ellenberger T. Sung P. Nature. 2003; 423: 305-309Crossref PubMed Scopus (503) Google Scholar, M. Nature. 2003; 423: PubMed Scopus Google Scholar, Y. B. G. M. Mol. Cell. Biol. 2003; PubMed Scopus Google Scholar, X. J. C. Kowalczykowski S.C. E. F. Nature. 2003; 423: PubMed Scopus Google Scholar, M. Science. 2003; PubMed Scopus Google Scholar). It to be seen Rad54 or in with factors in it can be with that the from the mechanism of HR in cancer and