Switch-domain mutations in the Saccharomyces cerevisiae G protein alpha-subunit Gpa1p identify a receptor subtype-biased mating defect.
The response to pheromone in Saccharomyces cerevisiae involves a heterotrimeric G protein composed of Gpa1p (alpha subunit), Ste4p (beta) and Ste18p (gamma). The switch II region of G alpha subunits is involved in several protein-protein interactions and an intrinsic GTPase activity. To investigate the role of this region of Gpa1p, we have analyzed the effect of switch II mutations. The Q323 analog in G alpha subunits and Ras is implicated in GTP hydrolysis. Mutation of the Q323 residue of Gpa1p resulted in constitutive activation of the pheromone response pathway and eliminated the ability to interact with Ste4p, consistent with a defect in GTPase activity. Mutation of residue A59 of Ras and the analogous G alphas residue has had quite different effects. The analogous Gpa1p G321T mutation resulted in phenotypes consistent with a less severe GTPase defect, but also led to an unexpected mating phenotype: mating was decreased in both mating types, but the defect was 1000-fold more severe in alpha cells than in a cells. In addition the G321T mutation resulted in an unusual pheromone response phenotype. We discuss the possibility that these phenotypes may reflect a differential role for the switch II region in activation by the a- and alpha-factor receptors.
DeSimone
S M
SM
Department of Microbiology and Molecular Genetics, Markey Center for Molecular Genetics, University of Vermont, Burlington 05405-0068, USA.
Kurjan
J
J
D005656:Fungal Proteins / Q000235:genetics* / Q000276:immunology; D044385:GTP-Binding Protein alpha Subunits; D043802:GTP-Binding Protein alpha Subunits, Gq-G11; D019204:GTP-Binding Proteins / Q000235:genetics* / Q000276:immunology; D005800:Genes, Fungal / Q000235:genetics*; D005812:Genes, Switch / Q000235:genetics*; D020962:Heterotrimeric GTP-Binding Proteins; D010641:Phenotype; D017354:Point Mutation / Q000235:genetics*; D011487:Protein Conformation; D012441:Saccharomyces cerevisiae / Q000235:genetics* / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins; D012724:Sex Attractants / Q000378:metabolism
D005656:Fungal Proteins; D044385:GTP-Binding Protein alpha Subunits; D029701:Saccharomyces cerevisiae Proteins; D012724:Sex Attractants; D019204:GTP-Binding Proteins; C084293:GPA1 protein, S cerevisiae; D043802:GTP-Binding Protein alpha Subunits, Gq-G11; D020962:Heterotrimeric GTP-Binding Proteins