Galpha protein dependent and independent effects of human RGS1 expression in yeast

Regulators of G-protein Signalling (RGS) regulate the functional lifetime of G-Protein Coupled Receptor (GPCR)-activated heterotrimeric G-protein by serving as GTPase Accelerating Proteins (GAPs) for the G(alpha) subunit. A number of mammalian RGSs can functionally replace the yeast RGS containing SST2 gene and inhibit GPCR signalling. Using yeast strains harbouring a G(betagamma)-responsive FUS1-LacZ reporter gene, we demonstrate that heterologously expressed mammalian RGS1 also serves to decrease basal signalling in the absence of agonist. Although this effect was dependent on the expression of a GPA1-encoded functional G(alpha) protein, the GPCR itself was nevertheless not required. Using the GAL1 inducible promoter to express RGS1, we further demonstrate that in addition to serving as a GAP for Gpa1p in yeast, RGS1 is a dosage-dependent inhibitor of growth. This effect is specific to RGS1 since growth is not altered in cells expressing either mammalian RGS2 or RGS5. We further demonstrate that neither of the two yeast G(alpha) proteins is responsible for mediating this growth inhibitory effect of RGS1. Taken together, our results indicate that RGS1 can function in both G-protein-dependent and -independent manners in yeast.