Genetic analysis reveals different roles of Schizosaccharomyces pombe sfr1/dds20 in meiotic and mitotic DNA recombination and repair.

DNA double-strand break (DSB) repair mediated by the Rad51 pathway of homologous recombination is conserved in eukaryotes. In yeast, Rad51 paralogs, Saccharomyces cerevisiae Rad55-Rad57 and Schizosaccharomyces pombe Rhp55-Rhp57, are mediators of Rad51 nucleoprotein formation. The recently discovered S. pombe Sfr1/Dds20 protein has been shown to interact with Rad51 and to operate in the Rad51-dependent DSB repair pathway in parallel to the paralog-mediated pathway. Here we show that Sfr1 is a nuclear protein and acts downstream of Rad50 in DSB processing. sfr1Delta is epistatic to rad18 (-) and rad60 (-), and Sfr1 is a high-copy suppressor of the replication and repair defects of a rad60 mutant. Sfr1 functions in a Cds1-independent UV damage tolerance mechanism. In contrast to mitotic recombination, meiotic recombination is significantly reduced in sfr1Delta strains. Our data indicate that Sfr1 acts in DSB repair mainly outside of S-phase, and is required for wild-type levels of meiotic recombination. We suggest that Sfr1 acts early in recombination and has a specific role in Rad51 filament assembly, distinct from that of the Rad51 paralogs.

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