The structure of transposable yeast mating type loci

Area of Science:

• Molecular Biology
• Yeast Genetics

Background:

• The mating type locus (MAT) in Saccharomyces cerevisiae determines yeast mating behavior.
• Silent mating type loci (HMR and HML) are known to influence the active MAT locus.

Purpose of the Study:

• To elucidate the structural organization and sequence homology of mating type loci in Saccharomyces cerevisiae.
• To investigate the DNA sequences involved in mating type interconversion.

Main Methods:

• Isolation of a recombinant plasmid containing the MAT alpha mating type locus.
• Hybridization studies using restriction fragments of MAT, HMR, and HML loci.
• Recombinant lambda clone isolation and heteroduplex analysis to compare locus structures.

Main Results:

• All mating type loci (MAT, HMR, HML) share common DNA sequences.
• Alpha-phenotype loci (MAT alpha, HML alpha) contain an 850 bp alpha-specific sequence; a-phenotype loci (MATa, HMRa) contain a 700 bp a-specific sequence.
• Homologous flanking regions of varying lengths exist, with HML alpha and HMRa showing differential homology to MAT loci.

Conclusions:

• The structural organization of mating type loci supports models of DNA transposition for mating type switching.
• Specific DNA sequences are characteristic of HML loci, regardless of their a- or alpha-specific content.
• These findings provide insights into the genetic mechanisms underlying mating type determination and switching in yeast.