Title: Control of yeast cell types by mobile genes: A test
Abstract: The yeast Saccharomyces cerevisiae changes cell types by switching the alleles of the mating type locus ( MAT ) from a to α and vice versa. In the cassette model, these switches—e.g., from a to α—occur when a replica of silent α information (an α “cassette”) replaces the resident a cassette at the mating type locus and is thereby expressed. We have identified a mutation in the locus postulated to be the silent α information ( HML α) and find that a mutation is introduced into the mating type locus as a result of interconversion: HML α - MAT α cells switch to MAT a and then to MAT α - . The MAT α - mutation leads to defective mating and behaves like some previously identified MAT α - mutations. These observations satisfy the prediction of the cassette and controlling element models that genetic information is transmitted from HML α to the mating type locus.