PRECISE MAPPING OF THE HOMOTHALLISM GENES HML AND HMR IN SACCHAROMYCES CEREVISIAE

Abstract

The HML and HMR loci carry unexpressed copies of MAT a and MATα information, and a replica of that information is transposed to MAT during mating-type interchange in Saccharomyces yeasts. A negative control mechanism keeps silent the information located at the HML and HMR loci. We mapped these loci by constructing strains in which these loci are expressed. In these strains, the mating type of the segregants is dependent upon the allele at HML and HMR. This novel approach is independent of their switching function. HML is located on the left arm of chromosome III distal to his4 by about 26.8 centimorgans (cM). HMR maps on the right arm of the same chromosome distal to thr4 by about 39.8 cM and proximal to MAL2 by about 1.0 cM. The results allow the exact placement of these loci and are in accord with the observations made by Harashima and Oshima (1976).

The Saccharomyces cerevisiae Chromosome III Left Telomere Has a Type X, but Not a Type Y′, ARS Region

“…The telomere previously isolated and characterized (9,15,16,27) is representative of the Y'-containing telomere class, although the existence of the Y'-lacking class has been spec- ulated (16,29,30). We report here the isola class telomere by chromosome walking from chromosome III left (IIIL) end (11,18,19,23). region, localized to a heterodisperse 1.8-kb (+ [bp]) EcoRI fragment on IIIL, consists of a 1. adjacent to a 0.6-kb (±200 bp) T region of 5'-C repeat sequence.…”

Mating Type Control in Saccharomyces cerevisiae: a Frameshift Mutation at the Common DNA Sequence, X, of the HMLα Locus

“…Mating type information is also coded for by two additional loci, HML and HMR, on the left (HML) and right (HMR) arms of the same chromosome, each ca. 65 centimorgans distal to the centromere (12,23). The HML and HMR loci each have two codominant alleles, HMLa and HMLa and HMRa and HMRa, like the MATa and MATa alleles of the MAT locus.…”