The msh2 Gene of Schizosaccharomyces pombe Is Involved in Mismatch Repair, Mating-Type Switching, and Meiotic Chromosome Organization

Abstract

We have identified in the fission yeast Schizosaccharomyces pombe a MutS homolog that shows highest homology to the Msh2 subgroup. msh2 disruption gives rise to increased mitotic mutation rates and increased levels of postmeiotic segregation of genetic markers. In bandshift assays performed with msh2Δ cell extracts, a general mismatch-binding activity is absent. By complementation assays, we showed that S. pombe msh2 is allelic with the previously identified swi8 and mut3 genes, which are involved in mating-type switching. The swi8-137 mutant has a mutation in the msh2gene which causes a truncated Msh2 peptide lacking a putative DNA-binding domain. Cytological analysis revealed that during meiotic prophase of msh2-defective cells, chromosomal structures were frequently formed; such structures are rarely found in the wild type. Our data show that besides having a function in mismatch repair,S. pombe msh2 is required for correct termination of copy synthesis during mating-type switching as well as for proper organization of chromosomes during meiosis.

ACKNOWLEDGMENTS

We thank Primo Schär, Peter Munz, Christiane Rayssiguier, Carine Tornier, and Monika Molnar for helpful discussions, Henning Schmidt and Kai Ostermann for kindly providing the swi8strains, and Elmar Maier for the cosmid clones.

This work was supported by the Swiss National Science Foundation.