Regulation of yeast mating-type interconversion: feedback control of HO gene expression by the mating-type locus

• Published in: Proceedings of the National Academy of Sciences - PNAS 1983-05, Vol.80 (10), p.3035-3039
• Main Authors: Jensen, Robert, Sprague, George F., Herskowitz, Ira
• Format: Article
• Language: English
• Subjects: Cells; Diploidy; DNA; DNA probes; DNA, Fungal - genetics; Feedback; Gene Expression Regulation; Genetic loci; Genetic mutation; Haploidy; Heterozygote; Plasmids; Recombination, Genetic; Reproduction; RNA; RNA, Fungal - genetics; Saccharomyces cerevisiae; Saccharomyces cerevisiae - genetics; Yeasts
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.80.10.3035

The ultimate product of yeast mating-type interconversion is a stable a/α diploid cell. A haploid cell carrying the HO gene gives rise to a diploid cell in a two-step process: first, the cell switches mating type as a result of genetic rearrangement (cassette substitution) catalyzed by HO; then, cells of opposite type mate to form a/α diploids. Mating-type interconversion does not occur in a/α diploids despite the presence of the HO gene. We have identified a plasmid carrying the HO gene by screening a yeast clone bank (constructed in vector YEp13) for plasmids that allow mating-type switching by ho cells. The yeast segment responsible for mating-type interconversion integrates by homology at the ho locus, thus confirming that it carries HO. Using the HO gene as a probe, we find that strains with an active mating-type interconversion system produce HO RNA, whereas a/α HO/HO cells do not and that this inhibition requires products of both the MATa1 and MATa2 genes. Thus, mating-type interconversion does not occur in a/α HO/HO cells because the HO gene product is not synthesized. These results demonstrate the following: (i) The mating-type locus, proposed on genetic grounds to be a regulatory locus, controls expression of an unlinked gene (HO) at the level of RNA production. (ii) The HO gene is under negative feedback control: its expression is inhibited after successful completion of diploidization (formation of a/α diploids).