title: Putative antirecombinase Srs2 DNA helicase promotes noncrossover homologous recombination avoiding loss of heterozygosity.
abstract: DNA damage alone or DNA replication fork arrest at damaged sites may induce DNA double-strand breaks and initiate homologous recombination. This event can result in a crossover with a homologous chromosome, causing loss of heterozygosity along the chromosome. It is known that Srs2 acts as an antirecombinase at the replication fork: it is recruited by the SUMO (a small ubiquitin-related modifier)-conjugated DNA-polymerase sliding clamp (PCNA) and interferes with Rad51/Rad52-mediated homologous recombination. Here, we report that Srs2 promotes another type of homologous recombination that produces noncrossover products only, in collaboration with PCNA and Rad51. Srs2 proteins lacking the Rad51-binding domain, PCNA-SUMO-binding motifs, or ATP hydrolysis-dependent DNA helicase activity reduce this noncrossover recombination. However, the removal of either the Rad51-binding domain or the PCNA-binding motif strongly increases crossovers. Srs2 gene mutations are epistatic to mutations in the PCNA modification-related genes encoding PCNA, Siz1 (a SUMO ligase) and Rad6 (a ubiquitin-conjugating protein). Knocking out RAD51 blocked this recombination but enhanced nonhomologous end-joining. We hypothesize that, during DNA double-strand break repair, Srs2 mediates collaboration between the Rad51 nucleofilament and PCNA-SUMO and directs the heteroduplex intermediate to DNA synthesis in a moving bubble. This Rad51/Rad52/Srs2/PCNA-mediated noncrossover pathway avoids both interchromosomal crossover and imprecise end-joining, two potential paths leading to loss of heterozygosity, and contributes to genome maintenance and human health.
authors.affiliation: Center for Genetic Resource Education and Development, Kyoto Institute of Technology, 1 Matsugasaki, Sakyo-ku, Kyoto 606-8585, Japan.
authors.forename: Tohru
authors.initials: T
authors.lastname: Miura
authors.forename: Takehiko
authors.initials: T
authors.lastname: Shibata
authors.forename: Kohji
authors.initials: K
authors.lastname: Kusano
mesh_terms: D053903:DNA Breaks, Double-Stranded; D004265:DNA Helicases / Q000235:genetics*; D017931:DNA Primers / Q000235:genetics; D055786:Gene Knockout Techniques; D059765:Homologous Recombination / Q000502:physiology*; D019656:Loss of Heterozygosity / Q000502:physiology*; D016297:Mutagenesis, Site-Directed; D012441:Saccharomyces cerevisiae / Q000201:enzymology*; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics*; D013045:Species Specificity
chemical_list: D017931:DNA Primers; D029701:Saccharomyces cerevisiae Proteins; C061376:SRS2 protein, S cerevisiae; D004265:DNA Helicases
keywords: NHEJ; SDSA; bubble migration
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