Control of sporulation in yeast: SAD1-a mating-type specific, unstable alteration that uncouples sporulation from mating-type control

Abstract

Normally, in order to sporulate, a diploid yeast cell must be heterozygous (MATa/MATα) at the mating-type locus. In a new mutant, this requirement is circumvented by SAD1. This alteration is mating-type specific; it allows sporulation of MATα/ MATα. MATα/mata-1, and MATα/matα-2 diploid cells, but not MATa/MATa or MATa/0 (monosomic) strains. Other than acquiring the ability to sporulate, SAD1 cells behave as wild-type MATα/MATα strains; they exhibit medial budding, normal mating factor production and response and mate with normal mating efficiencies and kinetics. The segregation of SAD1 is often bizarre; for example, MATα/MATα strains which were constructed to be heterozygous SAD1/+ often segregate 4 SAD1:0+progeny and strains which were constructed to be homozygous SAD1/ SAD1 sometimes segregated 1 SAD1:3+progeny. The genetic analyses of SAD1 suggest that it is dominant and is located ∼30 cM from MAT on chromosome III.