Regulation of Development in Fission Yeast
In the Yeast Schizosaccharomyces pombe, copulation and meiosis appear to be regulated by the mating-type genes, mat1 and mat2 (Leupold, Cold Spring Harbor Symp. Quant. Biol. 23: 161, 1958). A mat2 gene mutant, meI1, has been reported which is normal with respect to copulation but defective with respect to meiosis. From homothallic strains, we have isolated new mat2 mutants representing three additional groups: 1) mutants unable to self-copulate but still able to turn on the mating-type auxiliary gene maps and still normal with respect to the meiosis function; 2) mutants unable to self-copulate as they cannot turn on map1, but still normal with respect to the meiosis function; and 3) mutants which are nonfunctional both with respect to self-copulation and to meiosis. Furthermore, we have found a new group of genes which appear to regulate the activity of the mat1 and mat2 genes. Homothallic h 90 colonies normally exhibit a homogeneous black color after exposure to iodine vapors (non-sporulating colonies turn yellow). The mutants found in h 90 strains were neither homogeneously black nor yellow but rather were mottled in appearance. Further studies hint that this group of at least four genes may act as specific mutator genes for the mating-type region, changing the region from an active mat1--inactive mat2 to an inactive mat1--active mat2 and vice versa.