The genetic instabilities of the mating type locus in fission yeast

Abstract

Certain genetic instabilities of the “mating type locus” in the yeast Schizosaccharomyces pombe are interpreted in terms of transposition: Homothallic strains are characterized by two adjacent mating type genes (mat1 ⁻ mat2 ⁺) with sexually complementary functions. One of these genes (mat2 ⁺) is able to duplicate itself, and the duplicated copy maps at the position of mat1 ⁻. The former function of mat1 ⁻ is lost (owing to insertion), and only becomes reactivated when the inserted sequence (mat1 ⁺) is again excised. Analyses of analogous instabilities expressed by the partially defective mutation mat2 ⁺-B102 have substantiated this transposition scheme. Homothallism is acribed to alternate and mutually exclusive activation of mat1 ⁻ or mat2 ⁺ genes.