Genes required for initiation and resolution steps of mating-type switching in fission yeast.

Open Access
Publisher Website
Google Scholar
Abstract
The fission yeast S. pombe switches mating type by transposition of a copy of DNA derived from either of the 2 storage cassettes, mat2-P and mat3-M, into the expression locus, mat1. The recombinational event of switching is initiated by a double-stranded DNA break present in approximately 20% of the molecules at mat1. Mutants (53) defective in switching of mating type were isolated previously and each was assigned to 1 of 10 linkage groups. One group consists of cis-acting mutations at mat1, which reduce the amount of the DNA double-strand cut. The remaining 9 groups are mutations in genes that are unlinked to the mating-type locus and are studied here. Three (swil, -3, -7) are required for formation of the double-strand cut, whereas the others are not. Mutants of 3 genes (swi4, -8, -9) undergo high-frequency rearrangement of the mating-type locus indicative of errors of resolution of recombinational intermediates. The remaining 3 (swi2, -5, -6) have normal levels of cut, do not make errors of resolution, and possibly are required either for efficient utilization of the cut or determining the directionality of switching. The switching process can be dissected into genetically distinguishable steps.