Protein farnesylation is critical for maintaining normal cell morphology and canavanine resistance in Schizosaccharomyces pombe

Protein farnesyltransferase (FTase) plays important roles in the growth and differentiation of eukaryotic cells. In this paper, we report the identifi cation of the Schizosaccharomyces pombe gene cpp1(+) encoding the beta-subu nit of FTase. The predicted amino acid sequence of the cpp1(+) gene product shares significant similarity with FTase beta-subunits from a variety of o rganisms. S. pombe FTase purified from E. coli exhibits high enzymatic acti vity toward the CAAX farnesylation motif substrates (where C represents cys teine, A represents aliphatic amino acid, and X is preferentially methionin e, cysteine, serine, alanine, or glutamine) while showing little preference for CAAL geranylgeranylation motif substrates (where L represents leucine or phenylalanine). cpp1(+) is not essential for growth as shown by gene dis ruption; however, mutant cells exhibit rounded or irregular cell morphology , Expression of a geranylgeranylated mutant form, Ras1-CVIL, which can bypa ss farnesylation, rescues these morphological defects. We also identify a n ovel phenotype of cpp1(-) mutants, hypersensitivity to canavanine. This app ears to be due to a 3-4-fold increase in the rate of arginine uptake as com pared with wild-type cells. Expression of the geranylgeranylated mutant for m of a novel farnesylated small GTPase, SpRheb, is able to suppress the ele vated arginine uptake rate. These results demonstrate that protein farnesyl ation is critical for maintaining normal cell morphology through Ras1 and c anavanine resistance through SpRheb.