Sexual Differentiation Is Controlled by a Protein Kinase Encoded by the ran1⁺ Gene in Fission Yeast

Excerpt

Fission yeast is a haploid ascomycete that switches mating-type every few cell divisions during vegetative growth (Egel 1977; Beach 1983). Under conditions of nutrient deprivation, cells of opposite mating-type (h⁺ or h⁻), which have become arrested in the G₁ phase of the cell cycle, conjugate to form a diploid zygote (Egel 1971; Nurse and Bissett 1981). The zygote, now heterozygous at the mating-type locus (h⁺/h⁻), enters the premeiotic S phase and then undergoes two meiotic divisions that lead to the formation of a four-spored ascus.

Temperature-sensitive lethal mutations that allow haploid cells to sporulate have recently been described (Nurse 1985; Iino and Yamamoto 1985a,b). Loss of function of the ran1⁺ gene bypasses two normally essential requirements for sporulation: (1) heterozygosity at the mating-type locus and (2) nutritional deprivation. In this paper we summarize experiments that characterize the transition from vegetative growth to meiosis in normal diploid strains and compare this...