Expression of MF alpha 1 in MATa cells supersensitive to alpha-factor leads to self-arrest.

MATa cells of Saccharomyces cerevisiae defective in both the SST1 and SST2 gene products exhibit self-arrest when they express the MF alpha 1 gene under the control of the GAL1 promoter. This response to endogenously produced pheromone can be alleviated by mutations which prevent the production of, or response to, alpha-factor. Suppressors of the self-arrest phenotype include a class of mutants which remain responsive to low levels of pheromone, but are resistant to high levels of alpha-factor. One of these mutants has been mapped to chromosome X, 31 cM distal to SUP4, and defines a new locus designated STE18.