MATING-TYPE MUTATIONS IN SCHIZOSACCHAROMYCES POMBE: ISOLATION OF MUTANTS AND ANALYSIS OF STRAINS WITH AN h - or h + PHENOTYPE

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Abstract
Mutants defective in various steps of the sexual cycle have been isolated from homothallic strains of Schizosaccharomyces pombe by Bresch, Müller and Egel (1968). These mutants include heterothallic h + and h - strains. We have isolated additional h + and h -mutants from homothallic strains. Those mutants which are due to mutations in the mating-type region were analyzed in detail. Our results show that the mating-type gene mat2 not only has a function in copulation and meiosis, but that it also regulates the formation of the map1 gene product (map1 is a mating-type auxiliary gene). Some of the h - mutants have lost only one of the three functions while others are defective in at least two, and perhaps all three, functions. Further, we show that the mat1 - allele of h90 strains can mutate to mat1 + but that mutations in mat2 appear to affect the mutational behavior of mat1. Finally, we describe a new inactive mating-type allele, mat2*, which is different from mat2 0 in that it can mutate to mat2 +.

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