RHO gene products, putative small GTP-binding proteins, are important for activation of the CAL1/CDC43 gene product, a protein geranylgeranyltransferase in Saccharomyces cerevisiae.

Two multicopy suppressors of the cal1-1 mutation in the yeast Saccharomyces cerevisiae have been isolated and characterized. They are identical to the yeast RHO1 and RHO2 genes, which encode putative small GTP-binding proteins. Multiple copies of either RHO gene suppressed temperature-sensitive growth of the cal1-1 mutant but did not suppress the cal1 null mutant. Genetic analysis suggests that overproduction of either RHO gene product acts for activation of the CAL1 gene product.