The involvement of Srs2 in post-replication repair and homologous recombination in fission yeast

Homologous recombination is important for the repair of double-strand breaks and daughter strand gaps, and also helps restart stalled and collapsed replication forks. However, sometimes recombination is inappropriate and can have deleterious consequences. To temper recombination, cells have employed DNA helicases that unwind joint DNA molecules and/or dissociate recombinases from DNA. Budding yeast Srs2 is one such helicase. It can act by dissociating Rad51 nucleoprotein filaments, and is required for channelling DNA lesions to the post-replication repair (PRR) pathway. Here we have investigated the role of Srs2 in controlling recombination in fission yeast. Similar to budding yeast, deletion of fission yeast srs2 results in hypersensitivity to a range of DNA damaging agents, rhp51-dependent hyper-recombination and synthetic sickness when combined with rqh1(-) that is suppressed by deleting rhp51, rhp55 or rhp57. Epistasis analysis indicates that Srs2 and the structure-specific endonuclease Mus81-Eme1 function in a sub-pathway of PRR for the tolerance/repair of UV-induced damage. However, unlike in Saccharomyces cerevisiae, Srs2 is not required for channelling lesions to the PRR pathway in Schizosaccharomyces pombe. In addition to acting as an antirecombinase, we also show that Srs2 can aid the recombinational repair of camptothecin-induced collapsed replication forks, independently of PRR.