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Deletions and single base pair changes in the yeast mating type locus that prevent homothallic mating type
Summary
Mutations in Saccharomyces cerevisiae prevent mating type switching by altering DNA sequences near the Y/Z border. This region is crucial for efficient mating type allele conversion.
Area of Science:
- Molecular Biology
- Genetics
- Yeast Biology
Background:
- Homothallic mating type switching in Saccharomyces cerevisiae is a complex genetic process.
- Specific DNA sequences within the mating type (MAT) locus regulate this conversion.
- Understanding these regulatory sequences is key to deciphering mating type determination.
Purpose of the Study:
- To identify and characterize cis-acting mutations that disrupt mating type switching in yeast.
- To pinpoint the DNA regions essential for efficient MAT allele conversion.
- To elucidate the molecular mechanisms underlying mating type switching.
Main Methods:
- Generating deletions within the MAT locus in rad52 mutant yeast.
- Selecting for non-switching survivors to isolate mutations.
- DNA sequencing of spontaneous inc mutations.
- Restriction fragment analysis of mutated MAT loci.
Main Results:
- Several deletions and spontaneous mutations were found to prevent mating type switching.
- All deletions removed a Hha I restriction site at the Y alpha/Z border.
- Specific base pair substitutions in the Z region (Z2 and Z6) altered the Y alpha/Z border and disrupted switching.
Conclusions:
- The region near the Y/Z border is essential for efficient MAT allele switching.
- This region likely functions as an enzyme recognition site for nucleolytic cleavage of MAT DNA.
- Mutations affecting this site directly impair the mating type conversion process.