title: Mutations leading to expression of the cryptic HMRa locus in the yeast Saccharomyces cerevisiae.
abstract: Mutations leading to expression of the silent HMRa information in Saccharomyces cerevisiae result in sporulation proficiency in mata1/MAT alpha diploids. An example of such a mutation is sir5-2, a recessive mutation in the gene SIR5. As expected, haploids carrying the sir5-2 mutation are nonmaters due to the simultaneous expression of HMRa and HML alpha, resulting in the nonmating phenotype of an a/alpha diploid. However, sir5-2/sir5-2 mata1/MAT alpha diploids mate as alpha yet are capable of sporulation. The sir5-2 mutation is unlinked to sir1-1, yet the two mutations do not complement each other: mata1/MAT alpha sir5-2/SIR5 SIR1/sir1-1 diploids are capable of sporulation. In this case, recessive mutations in two unlinked genes form a mutant phenotype, in spite of the presence of the normal wild-type alleles. The PAS1-1 mutation, Provider of a Sporulation function, is a dominant mutation tightly linked to HMRa. PAS1-1 does not affect the mating ability of a strain, yet it allows diploids lacking a functional MATa locus to sporulate. It is proposed that PAS1-1 leads to partial expression of the otherwise cryptic a1 information at HMRa.
mesh_terms: D000818:Animals; D005786:Gene Expression Regulation; D005800:Genes, Fungal; D000072235:Mating Factor; D009154:Mutation; D010455:Peptides / Q000235:genetics; D010675:Pheromones / Q000235:genetics; D012441:Saccharomyces cerevisiae / Q000235:genetics*; D013172:Spores, Fungal
chemical_list: D010455:Peptides; D010675:Pheromones; D000072235:Mating Factor