Vanadate-resistant yeast mutants are defective in protein glycosylation

Spontaneous recessive orthovanadate-resistant mutants of Saccharomyces cerevisiae were obtained in five complementation groups, and all show defects in protein glycosylation that mimic the previously isolated mnn mutants. Three of the groups are allelic to the known mnn8, mnn9, and mnn10 mutants, whereas the other two groups show other glycosylation defects. The vanadate-resistant phenotype was associated with enhanced hygromycin B sensitivity. The glycosylation phenotypes of the mutants are all reflections of defects in glycoprotein trafficking, and the easy isolation of vanadate-resistant or hygromycin B-sensitive mutants should facilitate the study of this process.