Switching genes in Schizosaccharomyces pombe: their influence on cell viability and recombination

Summary In Schizosaccharomyces pombe, mutations in 10 swi genes are known which reduce but not abolish mating-type (MT) switching in homothallic (h⁹⁰) strains. Three classes (Ia, Ib, and II) of swi genes are distinguished. Three swi1 alleles are nonsense mutations. In strains with mutations in two or three swi genes, a cumulative reduction of MT switching only occurs if the genes belong to different classes. The class 1a combinations swi1 swi7 and swi3 swi7 are lethal. Besides its influence on MT switching, swi5 also reduces the frequencies of meiotic intragenic recombination and gene conversion in the ade6 locus.We dedicate this paper to Professor Kaudewitz on the occasion of his retirement