Activation of mating type genes by transposition in Saccharomyces cerevisiae.

Abstract

S. cerevisiae may express an a or .alpha. mating type. These cell types may be interconverted as a consequence of heritable genetic alterations at the mating type locus (MAT). According to the more general controlling element model [Oshima, Y and Takano], and the specific cassette model [Hicks, J., Strathern, J. and Herskowitz, I.], the regulatory information required for switching the MAT locus exists at 2 other loosely linked loci, HMa and HM.alpha.. Specifically, the HMa and HM.alpha. loci are proposed to carry silent .alpha. and silent a genes, respectively. According to these models, switching occurs when a replica of a silent gene replaces the resident information at the mating type locus and is thereby expressed. These models predict that mutations at the silent ("storage") loci would generate defective MAT loci subsequent to the switching process. The behavior of HM.alpha. mutants during the mating type interconversion was investigated. The results demonstrate that defective MATa alleles are generated by switching the MAT.alpha. locus in HM.alpha. mutants. Thus, the genetic information from HM.alpha. is transposed to the mating type locus. These results provide genetic evidence in support of these models.