Genetic characterization of an alpha-specific gene responsible for sexual agglutinability in Saccharomyces cerevisiae: mapping and gene dose effect.

A recessive ag alpha 1 mutation leads to specific defect in sexual agglutinability specifically in alpha cells of the yeast Saccharomyces cerevisiae. The cryptopleurine resistance gene cryR 1, closely linked to the mating type locus, was used to select alpha/alpha strains which emerged from alpha/alpha strains by mitotic nonreciprocal recombination, to genetically analyse ag alpha 1, since ag alpha 1 is expressed only in alpha mating type. The ag alpha 1 gene was found to be linked to the centromere tightly, to met3 at 4.4 cM, and to ilv 3 at 12 cM on chromosome X. Sexual agglutinability of alpha cells was shown to be dependent on the dose of the AG alpha 1 gene, using alpha/alpha isogenic strains carrying AG alpha 1/AG alpha 1, AG alpha 1/ag alpha 1 or ag alpha 1/ag alpha 1. The sst2-1 mutation did not suppress the ag alpha 1 mutation. Based on these results, function of the AG alpha 1 gene is discussed.