Schizosaccharomyces pombe exo1 is involved in the same mismatch repair pathway as msh2 and pms1

Abstract

Besides the MutLS-like system, Schizosaccharomyces pombe has an additional pathway of mismatch repair. This minor pathway, producing short excision tracts, repairs C/C and, with lower efficiency, other mismatches also. We investigated the involvement of the exol+, msh2+ and pmsl+ genes in the two pathways. The exol+ gene encodes a 5' to 3' exonuclease, while msh2+ and pmsl+ are homologs of Escherichia coli mutS and mutL, respectively. Intragenic two-factor crosses showed that exol+, msh2+ and pmsl+ are involved in the major, but not in the C/C-correcting, pathway. Post-meiotic segregation frequencies and mitotic mutation rates in single and double mutants supported this finding. Furthermore, msh2Δ was epistatic over exolΔ, and the Exol enzyme is likely to be redundant with other exonucleases.