Isolation and characterization of two novel ras superfamily genes in Saccharomyces cerevisiae.

We have isolated two novel genes, designated as RHO3 (on chromosome IX) and RHO4 (on chromosome XI), belonging to the ras superfamily, from the yeast Saccharomyces cerevisiae. Deletion of RHO4 did not affect cell growth, but deletion of RHO3 caused a severe growth delay and a decrease in cell viability. The rho3 and rho4 disrupted genes displayed synthetic lethality at 30 degrees C. RHO3 and RHO4 seem to have overlapping functions in cell growth, because the growth defect in rho3 cells was suppressed by overexpression of RHO4 despite the low homology (about 35%) at the amino acid sequence level between the RHO3 and RHO4 proteins.