A novel protein, R sf1/ P xd1, is critical for the single‐strand annealing pathway of double‐strand break repair in S chizosaccharomyces pombe

The process of single‐strand annealing ( SSA ) repairs DNA double‐strand breaks that are flanked by direct repeat sequences through the coordinated actions of a series of proteins implicated in recombination, mismatch repair and nucleotide excision repair ( NER ). Many of the molecular and mechanistic insights gained in SSA repair have principally come from studies in the budding yeast S accharomyces cerevisiae . However, there is little molecular understanding of the SSA pathway in the fission yeast S chizosaccharomyces pombe . To further our understanding of this important process, we established a new chromosome‐based SSA assay in fission yeast. Our genetic analyses showed that, although many homologous components participate in SSA repair in these species indicating that some evolutionary conservation, S aw1 and S lx4 are not principal agents in the SSA repair pathway in fission yeast. This is in marked contrast to the function of S aw1 and S lx4 in budding yeast. Additionally, a novel genus‐specific protein, R sf1/ P xd1, physically interacts with R ad16, S wi10 and S aw1 in vitro and in vivo . We find that R sf1/ P xd1 is not required for NER and demonstrate that, in fission yeast, R sf1/ P xd1, but not S aw1, plays a critical role in SSA recombination.