A mutation affecting sexual agglutinability in MATα locus of Saccharomyces cerevisiae.

A temperature-sensitive non-agglutinative mutant of Saccharomyces cerevisiae was isolated and characterized. The mutation, sag2, affected sexual agglutination, conjugation and production of α-mating pheromone at a restrictive temperature, but not the response to α-mating pheromone. Genetic analyses showed that the mutation was recessive and in the MATα locus. The sag2 mutation complemented with matα2 but not with matα1 These results suggest that sag2 is in the MATα1 gene and that at a restrictive temperature the mutation, sag2, inactivated the MATα1 product, a positive regulator of α-mating functions. The sag2 mutation is like matα1-5 in its retention of response to α-mating pheromone. However, at 25 °C, sag2 cells were competent to mate, whereas matα1-5 cells were not. Hence, sag2 is regarded as a new allele in the MATα1 gene, which we designate matα1-11.