Initiation of Sporulation in Saccharomyces cerevisiae. Mutations Causing Derepressed Sporulation and G1 Arrest in the Cell Division Cycle

Abstract

S. cerevisiae mutants derepressed for meiosis and spore formation were isolated and genetically characterized. All are the result of single, recessive nuclear mutations that fall into 4 linkage groups. Three of these groups are represented by spd1, spd3, and spd4 mutations, which in homozygous diploids confer poor growth and extensive sporulation on a range of non-fermentable media. Haploids carrying any of these mutations are arrested under these conditions in the G1 phase of the cell division cycle as large unbudded cells. The alleles of spd2 mutation complemented all other mutations but were very closely linked to the spd1 locus. The 4th linkage group was represented by a mutation conferring temperature-sensitive growth and derepressed sporulation on homozygous diploids grown between 25.degree. and 30.degree. C on media containing galactose or glycerol, but not glucose, as energy source. Above 30.degree. C, this mutant lysed on all media. The mutation it carried failed to complement available cdc25 mutations. These data bring to 5 the number of loci at which mutation can lead to derepressed sporulation (spd1, spd3, spd4, cdc25 and cdc35). The spdl locus mapped 13.9 centimorgans to the left of the centromere on chromosome XV, adjacent to the SUP3 gene. Diploid strains homozygous for spd mutations are genetically unstable, giving rise to asporogenous mutants at high frequency, usually as the result of a 2nd mutation unlinked to the spd mutation. Diploids homozygous for these mutations, and for spd mutations, show an altered regulation of the formulation of at least 3 polypeptides normally subject to C source repression.