The essential yeast NLT1 gene encodes the 64 kDa glycoprotein subunit of the oligosaccharyl transferase

The yeast oligosaccharyl transferase catalyzes the glycosylation of asparagine residues in secreted, vesicular, and membrane proteins. A complex of at least four membrane-bound polypeptides is responsible for oligosaccharyl transferase activity. Amino acid sequences from the 64 kDa glycoprotein subunit of the complex were used to clone the essential NLT1 (N-linked oligosaccharyl transferase) gene. The Nlt1p gene product is a processed, multiply glycosylated type I membrane protein; it has an extensive amino-terminal soluble domain, a potential hydrophobic transmembrane domain, and a short carboxy-terminal soluble domain. The Nlt1p is significantly similar than the mammalian ribophorin I, a component of the mammalian oligosaccharyl transferase complex, and the enzyme is conserved throughout eukaryotic evolution.