Transposable mating type genes in Saccharomyces cerevisiae

Abstract

A functional copy of the α mating type gene of Saccharomyces cerevisiae has been cloned by transformation in yeast. Using the Southern blotting procedure it has been shown that three distinct genetic loci implicated in mating type interconversion (HML, HMR and MAT) contain sequences homologous to the cloned fragment. The restriction fragment associated with each locus exhibits a characteristic size which can be correlated with the mating type allele present at that locus. The characteristic size difference between the a and α genetic elements made it possible to demonstrate that the homothallic interconversion of mating types in this yeast occurs by DNA rearrangement as proposed in the ‘cassette hypothesis’.