The alpha subunit of the Saccharomyces cerevisiae oligosaccharyltransferase complex is essential for vegetative growth of yeast and is homologous to mammalian ribophorin I
UMass Chan Affiliations
Department of Biochemistry and Molecular BiologyDocument Type
ArticlePublication Date
1995-02-01Keywords
Amino Acid SequenceAsparagine
Base Sequence
Fungal Proteins
Genes, Fungal
Genes, Lethal
Genomic Library
Glycosylation
HSP70 Heat-Shock Proteins
*HexosyltransferasesMembrane ProteinsMicrosomesMolecular Sequence DataMutagenesisOligosaccharidesProtein ConformationProtein Processing, Post-TranslationalSaccharomyces cerevisiaeSequence Analysis, DNASequence Homology, Amino AcidTransferasesBiochemistryCell BiologyMolecular Biology
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Oligosaccharyltransferase mediates the transfer of a preassembled high mannose oligosaccharide from a lipid-linked oligosaccharide donor to consensus glycosylation acceptor sites in newly synthesized proteins in the lumen of the rough endoplasmic reticulum. The Saccharomyces cerevisiae oligosaccharyltransferase is an oligomeric complex composed of six nonidentical subunits (alpha-zeta), two of which are glycoproteins (alpha and beta). The beta and delta subunits of the oligosaccharyltransferase are encoded by the WBP1 and SWP1 genes. Here we describe the functional characterization of the OST1 gene that encodes the alpha subunit of the oligosaccharyltransferase. Protein sequence analysis revealed a significant sequence identity between the Saccharomyces cerevisiae Ost1 protein and ribophorin I, a previously identified subunit of the mammalian oligosaccharyltransferase. A disruption of the OST1 locus was not tolerated in haploid yeast showing that expression of the Ost1 protein is essential for vegetative growth of yeast. An analysis of a series of conditional ost1 mutants demonstrated that defects in the Ost1 protein cause pleiotropic underglycosylation of soluble and membrane-bound glycoproteins at both the permissive and restrictive growth temperatures. Microsomal membranes isolated from ost1 mutant yeast showed marked reductions in the in vitro transfer of high mannose oligosaccharide from exogenous lipid-linked oligosaccharide to a glycosylation site acceptor tripeptide. Microsomal membranes isolated from the ost1 mutants contained elevated amounts of the Kar2 stress-response protein.Source
J Cell Biol. 1995 Feb;128(4):525-36.Permanent Link to this Item
http://hdl.handle.net/20.500.14038/42617PubMed ID
7860628Related Resources
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