suppressor of mating-type locus mutations in Saccharomyces cerevisiae : Evidence for and identification of cryptic mating-type loci

• Published in: Genetics (Austin) Vol. 93; no. 4; pp. 877 - 901
• Main Authors: Rine, J, Strathern, J.N, Hicks, J.B, Herskowitz, I
• Format: Journal Article
• Language: English
• Published: United States Genetics Soc America 01.12.1979
• Subjects: Chromosome Mapping; Investigations; Mutation; Phenotype; Saccharomyces cerevisiae - genetics; Saccharomyces cerevisiae - physiology; Spores, Fungal; Suppression, Genetic; yeasts
• ISSN: 0016-6731; 1943-2631; 1943-2631
• DOI: 10.1093/genetics/93.4.877

A mutation has been identified that suppresses the mating and sporulation defects of all mutations in the mating-type loci of S. cerevisiae. This suppressor, sir1-1, restores mating ability to mat alpha 1 and mat alpha 2 mutants and restores sporulation ability to mat alpha 2 and mata1 mutants. MATa sir1-1 strains exhibit a polar budding pattern and have reduced sensitivity to alpha-factor, both properties of a/alpha diploids. Furthermore, sir1-1 allows MATa/MATa, mat alpha 1/mat alpha/, and MAT alpha/MAT alpha strains to sporulate efficiently. All actions of sir1-1 are recessive to SIR1. The ability of sir1-1 to supply all functions necessary for mating and sporulation and its effects in a cells are explained by proposing that sir1-1 allows expression of mating type loci which are ordinarily not expressed. The ability of sir1-1 to suppress the mat alpha 1-5 mutation is dependent on the HMa gene, previously identified as required for switching of mating types from a to alpha. Thus, as predicted by the cassette model, HMa is functionally equivalent to MAT alpha since it supplies functions of MAT alpha. We propose that sir1-1 is defective in a function. Sir ("Silent-information regulator"), whose role may be to regulate expression of HMa and HM alpha.