GPA1^Val-50 Mutation in the Mating-Factor Signaling Pathway in Saccharomyces cerevisiae

Abstract

The GPA1 gene of Saccharomyces cerevisiae encodes a protein that is highly homologous to the α subunit of mammalian hetrotrimeric G proteins and is essential for haploid cell growth. A mutation of the GPA1 protein, GPAl^Val-50, in which Gly-50 was replaced by valine, could complement the growth defect of a GPA1 disruption, gpa1::HIS3. However, cells with gpa1::HIS3 expressing the GPA1^Val-50 protein were supersensitive to α-factor in a short-term incubation but resumed growth after long-term incubation even after exposure to high concentrations of α-factor. The former phenotype associated with GPA1^Val-50 is recessive, and the latter phenotype is dominant to GPA1 ⁺. The supersensitivity of GPA1^Val-50 to α-factor was dependent on STE2 and STE4, which demonstrates that this GPA1^Val-50-produced phenotype requires the mating-factor receptor and the β subunit of the G protein. The double mutant of sst2-1 GPA1^Val-50 recovered from division arrest, which suggested that SST2 is not required for recovery of the GPA1^Val-50 mutant.