[New approach to reveal genes that control cell wall biogenesis of the yeast Saccharomyces cerevisiae].

The Mcd4 protein of Saccharomyces cerevisiae is probably involved in addition of the phosphoethanolamine moiety to the first mannose residue of the glycosylphosphatidylinositol precursor(s). However, significance of this modification is unclear. Besides, functions of the MCD4 gene also is not completely clear, since mutations in this gene may have pleiotropic manifestations, which are not obviously related to the glycosylphosphatidylinositol biosynthesis. To clarify the functions of Mcd4p we have performed a search for genes whose mutations are lethal or semilethal in combination with the ssu21 mutation in MCD4. In total, we have isolated six mutations some of which cause sensitivity to SDS and/or calcofluor white. Genes which are able to complement two of these mutations were cloned. They were MNN9 which encodes protein involved in formation of outer chains of the N-linked glycans of secretory proteins and GWT1, encoding the protein of the endoplasmic reticulum involved in the glycosylphosphatidylinositol biosynthesis. The results obtained indicate that in both cases growth inhibition was caused by defect of cell wall biogenesis and alteration of folding of secretory proteins. Search for mutations that lethal in combination with the ssu21 is an effective approach to reveal genes involved in the control of cell wall biogenesis.