Abstract
Studies of heterothallic and homothallic strains of Saccharomyces cerevisiae have led to the suggestion that mating-type information is located at three distinct sites on chromosome 3, although only information at the mating-type (MAT) locus is expressed (Hicks, Strathern and Herskowitz, 1977). We have found that the recessive mutation cmt permits expression of the normally silent copies of mating-type information at the HMa and HMα loci. In haploid strains carrying HMa and HMα, the cmt mutation allows the simultaneous expression of both a and α information, leading to a nonmating ("MATa/MATα") phenotype. The effects of cmt can be masked by changing the mating-type information at HMa or HMα. For example, a cell of genotype MATa hma HMα cmt has an a mating type, while a MATα hma HMα cmt strain is nonmating. Expression of mating-type information at the HM loci can correct the mating and sporulation defects of the mata* and matα10 alleles. Meiotic segregants recovered from cmt/cmt diploids carrying the mat mutations demonstrate that these mutants are not "healed" to normal MAT alleles, as is the case in parallel studies using the homothallism gene HO.—All of the results are consistent with the notion that the HMa and hmα alleles both code for α information, while HMα and hma both code for a information. The cmt mutation demonstrates that these normally silent copies of mating-type and sporulation information can be expressed and that the information at these loci is functionally equivalent to that found at MAT. The cmt mutation does not cause interconversions of mating-type alleles at MAT, and it is not genetically linked to MAT, HMa, HMα or HO. In cmt heterozygotes, cmt becomes homozygous at a frequency greater than 1% when the genotype at the MAT locus in mata*/MATα or matα10/MATa.
Full Text
The Full Text of this article is available as a PDF (1.4 MB).
Selected References
These references are in PubMed. This may not be the complete list of references from this article.
- Gunge N., Nakatomi Y. Genetic Mechanisms of Rare Matings of the Yeast SACCHAROMYCES CEREVISIAE Heterozygous for Mating Type. Genetics. 1972 Jan;70(1):41–58. doi: 10.1093/genetics/70.1.41. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Haber J. E. Bisexual mating behavior in a diploid of Saccharomyces cerevisiae: evidence for genetically controlled non-random chromosome loss during vegetative growth. Genetics. 1974 Nov;78(3):843–858. doi: 10.1093/genetics/78.3.843. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Harashima S., Nogi Y., Oshima Y. The genetic system controlling homothallism in Saccharomyces yeasts. Genetics. 1974 Aug;77(4):639–650. doi: 10.1093/genetics/77.4.639. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Harashima S., Oshima Y. Mapping of the homothallic genes, HM alpha and HMa, in Saccharomyces yeasts. Genetics. 1976 Nov;84(3):437–451. doi: 10.1093/genetics/84.3.437. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Hopper A. K., Hall B. D. Mutation of a heterothallic strain to homothallism. Genetics. 1975 May;80(1):77–85. doi: 10.1093/genetics/80.1.77. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Kassir Y., Simchen G. Regulation of mating and meiosis in yeast by the mating-type region. Genetics. 1976 Feb;82(2):187–206. doi: 10.1093/genetics/82.2.187. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Mackay V., Manney T. R. Mutations affecting sexual conjugation and related processes in Saccharomyces cerevisiae. II. Genetic analysis of nonmating mutants. Genetics. 1974 Feb;76(2):273–288. doi: 10.1093/genetics/76.2.273. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Manuilova E. S., Shapiro N. I. Izuchenie geneticheskogo kontrolia chuvstvitel'nosti kletok mlekopitaiushchikh k letal'nomu i mutagennomu deistviiu ul'trafioletovykh luchei. Genetika. 1973 Nov;9(11):82–89. [PubMed] [Google Scholar]