Mating factor dependence of G1 cell cycle mutants of Saccharomyces cerevisiae

Mutants in four G1 cdc strains of Saccharomyces cerevisiae were isolated which failed to show division arrest in the presence of -factor. The cell cycle properties, terminal arrest morphology and mating competence of these mutants at the restrictive temperature were examined. The G1 specific arrest of the cdc 36 and cdc39 mutants is dependent upon the availability of an intact mating factor response system in Mat a cells. Cdc28 and cdc37 mutants exert their cell cycle blocks independently of the mating factor pathway. It is likely that the nature of the primary growth defect in cdc36 and cdc39 mutants is such that the -factor pathway is activated in the absence of the pheromone at the restrictive temperature and that G1 arrest is a secondary consequence of a non-cycle specific event in such mutants.