Mutual Repression of Haploid Genes in Diploid Yeast

Abstract

THE expression of the same genes can be studied in both haploid and diploid cells of certain yeasts. If the genes control primarily haploid mating type traits, then it is interesting to know whether these genes are expressed in the diploid which does not mate. In the agglutinative yeast, Hansenula wingei, the two haploid mating types (strains 5 and 21) produce cell surface glycoproteins which are complementary and which are responsible for the strong adhesion between cells during sexual agglutination^1–3. The diploid hybrid, however, is completely non-agglutinative. This lack of agglutination in the diploid could be the result of a mutual repression of the synthesis of both complementary agglutination factors, or synthesis followed by mutual neutralization or inactivation of these glycoproteins. We have evidence that the genes controlling the haploid agglutination types are mutually repressed in the diploid.