Mating-induced mating-type cassette conversion in Saccharomyces cerevisiae.

Area of Science:

• Molecular and Cellular Biology
• Yeast Genetics
• Epigenetics

Background:

• Previous work showed a specific yeast strain fragment's mobility changes upon mating.
• This fragment's behavior was linked to the sir4-11 mutation and rho degrees status.

Purpose of the Study:

• To investigate the mechanism behind mating-type cassette conversion in Saccharomyces cerevisiae.
• To determine the role of the sir4-11 mutation and rho degrees status in this conversion.
• To identify the conditions under which mating-type conversion occurs across all loci.

Main Methods:

• Genetic crosses involving specific Saccharomyces cerevisiae strains with defined mating-type loci (HML, MAT, HMR) and mutations (sir4-11).
• Analysis of restriction fragment electrophoretic mobility to detect changes in mating-type loci.
• Genotyping of resulting diploid strains to confirm mating-type cassette conversions.

Main Results:

• The rho degrees status of the sir4-11 strain is not essential for the observed mating-type conversion.
• The altered fragment contained HMRalpha instead of HMRa, indicating conversion at the HMR locus.
• Conversion of HMLa to HMLalpha and MATa to MATalpha was observed in specific crosses, particularly when loci were non-silenced.

Conclusions:

• A subset of Saccharomyces cerevisiae strains possesses factors that induce the conversion of a mating-type cassettes to alpha mating-type.
• This mating-type cassette conversion can occur at all three loci (HML, MAT, HMR) provided they are in a non-silenced state.
• The sir4-11 mutation and rho degrees status are not prerequisites for this mating-type conversion phenomenon.