A novel yeast mutant defective in the processing of ras proteins: assessment of the effect of the mutation on processing steps.

Biosynthesis of RAS1 and RAS2 proteins of Saccharomyces cerevisiae involves processing, fatty acid acylation and transport to plasma membranes. We now report the isolation of a mutant, termed dpr1, defective in these biosynthetic events. The dpr1 cells are temperature sensitive for growth and display sterile phenotype specific to a cells. The following observations were made using cells overproducing the RAS2 protein. (i) In the dpr1 cells, the RAS2 proteins remain as precursors and accumulate in the cytoplasm. (ii) The level of the RAS2 proteins in the plasma membrane of the dpr1 cells is much lower than that in the plasma membrane of wild-type cells. (iii) Fatty acid acylation appears to take place in the dpr1 cells. These results suggest that the major effect of the dpr1 mutation is in the processing of the precursor proteins, but not in their fatty acid acylation. Mutants such as dpr1 should be invaluable for further elucidation of the mechanisms of biosynthesis and transport of the RAS proteins, and presumably also a factor.