Role ofRAD52Epistasis Group Genes in Homologous Recombination and Double-Strand Break Repair

Abstract

The process of homologous recombination is a major DNA repair pathway that operates on DNA double-strand breaks, and possibly other kinds of DNA lesions, to promote error-free repair. Central to the process of homologous recombination are the RAD52 group genes (RAD50, RAD51, RAD52, RAD54, RDH54/TID1, RAD55, RAD57, RAD59, MRE11, and XRS2), most of which were identified by their requirement for the repair of ionizing-radiation-induced DNA damage in Saccharomyces cerevisiae. The Rad52 group proteins are highly conserved among eukaryotes, and Rad51, Mre11, and Rad50 are also conserved in prokaryotes and archaea. Recent studies showing defects in homologous recombination and double-strand break repair in several human cancer-prone syndromes have emphasized the importance of this repair pathway in maintaining genome integrity. Although sensitivity to ionizing radiation is a universal feature of rad52 group mutants, the mutants show considerable heterogeneity in different assays for recombinational repair of double-strand breaks and spontaneous mitotic recombination. Herein, I provide an overview of recent biochemical and structural analyses of the Rad52 group proteins and discuss how this information can be incorporated into genetic studies of recombination

Genetic evidence for a role of Saccharomyces cerevisiae Mph1 in recombinational DNA repair under replicative stress

“…The lagging strand could provide a template for elongation of the terminated leading strand. Reinstalling of the replication fork via HR could proceed by invasion of the terminated strand into the sister chromatid duplex and elongation of the 3 end, followed by disruption of the D-loop in a mechanism similar to synthesis-dependent strand annealing (SDSA; Symington, 2002). Another type of DNA damage arising during DNA synthesis and manageable by HR are double-stranded ends.…”

Synergistic action of the Saccharomyces cerevisiae homologous recombination factors Rad54 and Rad51 in chromatin remodeling

“…Genetic studies have found an involvement of Rad54 protein in homologous recombination and the DNA homology-directed elimination of DNA breaks and other chromosome lesions [3,17]. Consistent with the genetic data, studies with purified proteins have shown synergistic interactions of Rad54 with Rad51, in a manner that (1) greatly improves the ability of Rad51 to mediate the DNA strand invasion reaction with both naked and chromatinized DNA templates, and (2) enhances the ATPase, DNA supercoiling, DNA strand opening, DNA branch migration, and chromatin remodeling functions of Rad54 [9,10,[12][13][14]16].…”

“…Like many members of the Swi2/Snf2 protein family, Rad54 remodels chromatin structure, and this chromatin remodeling activity requires ATP hydrolysis [12][13][14]. Moreover, Rad54 utilizes the free energy from ATP hydrolysis to accelerate the DNA strand transfer reaction [15,16] and to process branched DNA structures [16], including the Holliday junction [16], that are expected to be generated during certain HR reactions [17].…”

“…D-loop formation is catalyzed by a recombinase enzyme, either Rad51 or Dmc1 [18], in a reaction termed homologous DNA pairing [17,19,20]. Like their prokaryotic counterparts E. coli RecA and T4 UvsX, Rad51 and Dmc1 form a filamentous structure, referred to as the presynaptic filament, on ssDNA [18,19].…”

“…Assembly of the presynaptic filament requires ATP binding by the recombinase protein [19,20], and ATP hydrolysis by the DNA-bound recombinase promotes the turnover of the presynaptic filament [21][22][23][24]. All the subsequent biochemical steps, including the capture of the duplex DNA partner and the search for homology in the engaged ssDNA and dsDNA molecules, that lead to D-loop formation occur within the confines of the presynaptic filament [17,19,20]. Thus, the presynaptic filament represents the key catalytic recombinase-DNA complex critical for the successful initiation and completion of the HR reaction.…”