Mutants of that are derepressed for meiosis and spore formation have been isolated and characterized genetically. All are the result of single, recessive nuclear mutations that fall into four linkage groups. Three of these groups are represented by and 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 the mutation complemented all other mutations but were very closely linked to the locus. The fourth linkage group was represented by a mutation conferring temperature-sensitive growth and derepressed sporulation on homozygous diploids grown between 25 °C and 30 °C on media containing galactose or glycerol, but not glucose, as energy source. Above 30 °C this mutant lysed on all media. The mutation it carried failed to complement available mutations. These data bring to five the number of loci at which mutation can lead to derepressed sporulation ( and ). The locus has been mapped 13.9 cM to the left of the centromere on chromosome XV, adjacent to the gene. Diploid strains homozygous for mutations are genetically unstable, giving rise to asporogenous mutants at high frequency, usually as the result of a second mutation unlinked to the mutation. Diploids homozygous for these mutations, and for mutations, show an altered regulation of the formulation of at least three polypeptides normally subject to carbon source repression.


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