A recessive mutant allele, mef1-84, of a novel locus mapping on the left arm of chromosome I, between ade3 and ura1, 5 cM apart from lys5, confers temperature-sensitive growth and mating deficiency at the non-restrictive temperatures for growth. Two other mutations suppress the phenotype conferred by mef1-84: sts1-1 suppresses the temperature-sensitive growth only, and smd1-35 suppresses both temperature-sensitive growth and mating deficiency.