Homo- and heterothallic sexual types in Schizosaccharomyces pombe var. malidevorans

Summary Although some differences are remarkable, the sexual system of Schizosaccharomyces pombe var. malidevorans is, in principle, compatible with that of Schizosaccharomyces pombe var. pombe. It has two heterothallic types analogous to Leupold's h ⁺ h^–, and a homothallic type, called spotty, which resembles h ⁹⁰. In addition, pseudoheterothallic types (pseudo-h ^– and pseudo-h ⁺) similar to certain mutants of S.p.v. pombe defective in conjugation were also found, as well as a homothallic type (grey) which has not been described in S. p. v. pombe. Genetic analysis of various hybrids constructed by mating and protoplast fusion revealed the probable genetic determination of the sexual types. Assuming a mating-type region similar to that of S.p.v. pombe, a five-gene-system can be supposed. The mat-locus is the residence of the expressible mating type information (either plus or minus), one gene determines whether the clone is homo- or heterothallic, another one regulates the intensity of mating and sporulation, and two are responsible for accomplishing certain mating-type dependent conjugation functions.