THE ESSENTIAL YEAST NLT1 GENE ENCODES THE 64-KDA GLYCOPROTEIN SUBUNITOF THE OLIGOSACCHARYL TRANSFERASE

The yeast oligosaccharyl transferase catalyzes the glycosylation of as paragine residues in secreted, vesicular, and membrane proteins, A com plex of at least four membrane-bound polypeptides is responsible for o ligosaccharyl transferase activity, Amino acid sequences from the 64 k Da glycoprotein subunit of the complex were used to clone the essentia l NLT1 (N-linked oligosaccharyl transferase) gene, The Nlt1p gene prod uct is a processed, multiply glycosylated type I membrane protein; it has an extensive amino-terminal soluble domain, a potential hydrophobi c transmembrane domain, and a short carboxy-terminal soluble domain, T he Nlt1p is significantly similar than the mammalian ribophorin I, a c omponent of the mammalian oligosaccharyl transferase complex, and the enzyme is conserved throughout eukaryotic evolution.