Sodium orthovanadate-resistant mutants of Saccharomyces cerevisiae show defects in Golgi-mediated protein glycosylation, sporulation and detergent resistance.

Orthovanadate is a small toxic molecule that competes with the biologically important oxyanion orthophosphate. Orthovanadate resistance arises spontaneously in Saccharomyces cerevisiae haploid cells by mutation in a number of genes. Mutations selected at 3 nM sodium orthovanadate have different degrees of vanadate resistance, hygromycin sensitivity, detergent sensitivity and sporulation defects. Recessive vanadate-resistant mutants belong to at least six genetic loci. Most mutants are defective in outer chain glycosylation of secreted invertase (van1, van2, van4, van5, van6, VAN7-116 and others), a phenotype found in some MNN or VRG mutants. The phenotypes of these vanadate-resistant mutants are consistent with an alteration in the permeability or specificity of the Golgi apparatus. The previously published VAN1 gene product has a 200 amino acid domain with 40% identity with the MNN9 gene product and 70% identity with the ANP1 gene product. Cells containing the van1-18, mnn9 (vrg6) or anp1 mutations have some phenotypic similarities. The VAN2 gene was isolated and its coding region is identified and reported. It is an essential gene on chromosome XV and its translated amino acid sequence predicts a unique 337 amino acid protein with multiple transmembrane domains.