Mutations in the CYS4 gene provide evidence for regulation of the yeast vacuolar H+-ATPase by oxidation and reduction in vivo.

The vma41-1 mutant was identified in a genetic screen designed to identify novel genes required for vacuolar H+-ATPase activity in Saccharomyces cerevisiae. The VMA41 gene was cloned and shown to be allelic to the CYS4 gene. The CYS4 gene encodes the first enzyme in cysteine biosynthesis, and in addition to cysteine auxotrophy, cys4 mutants have much lower levels of intracellular glutathione than wild-type cells. cys4 mutants display the pH-dependent growth phenotypes characteristic of vma mutants and are unable to accumulate quinacrine in the vacuole, indicating loss of vacuolar acidification in vivo. The vacuolar proton-translocating ATPases (V-ATPase) is synthesized at normal levels and assembled at the vacuolar membrane in cys4 mutants, but its specific activity is reduced (47% of wild type) and the activity is unstable. Addition of reduced glutathione to the growth medium complements the pH-dependent growth phenotype, partially restores vacuolar acidification, and restores wild type levels of ATPase activity. The CYS4 gene was deleted in a strain in which the catalytic site cysteine residue implicated in oxidative inhibition of the yeast V-ATPase has been mutagenized (Liu, Q., Leng, X.-H., Newman, P., Vasilyeva, E., Kane, P. M., and Forgac, M. (1997) J. Biol. Chem. 272, 11750-11756). This catalytic site point mutation suppresses the effects of the cys4 mutation. The data indicate that the acidification defect of cys4 mutants arises from inactivation of the vacuolar ATPase in the less reducing cytosol resulting from loss of Cys4p activity and provide the first evidence for the modulation of V-ATPase activity by the redox state of the environment in vivo.