Duplicated genes producing transposable controlling elements for the mating-type differentiation in Saccharomyces...

Area of Science:

• * Molecular Biology
• * Genetics
• * Yeast Biology

Background:

• * Homothallic genes (HML and HMR) in Saccharomyces cerevisiae control mating-type switching.
• * Understanding the mechanisms of mutation in these genes is crucial for yeast genetics.

Purpose of the Study:

• * To investigate the types and mechanisms of mutations occurring in the HML alpha/HMLa and HMRa/HMR alpha genes.
• * To explore the role of these mutations in the transition from heterothallism to homothallism.
• * To evaluate existing models of mating-type differentiation.

Main Methods:

• * Analysis of mutations in HML alpha and HMRa genes in homothallic yeast strains.
• * Use of ethyl methanesulfonate (EMS) for mutagenesis.
• * Observation of phenotypic reverse mutations and transition from heterothallism to homothallism.

Main Results:

• * Identified functional and nonfunctional mutations in HML alpha, with functional mutations predominating.
• * Observed only functional mutations (HMRa to HMR alpha) in the HMRa gene.
• * Demonstrated that mutation from heterothallism to homothallism occurred specifically in a nonfunctional HML alpha mutant.
• * Phenotypic reverse mutations were also observed.

Conclusions:

• * Functional mutations in homothallic genes are likely caused by the replacement of transposable elements, rather than direct allele conversion.
• * These findings support the controlling-element and cassette models for mating-type differentiation in yeast.
• * Nonfunctional mutations in HML alpha can facilitate the transition to homothallism.