THE N-OLIGOSACCHARYLTRANSFERASE COMPLEX FROM YEAST

N-Oligosaccharyltransferase catalyzes the N-glycosylation of asparagin e residues of nascent polypeptide chains in the endoplasmic reticulum, a pathway highly conserved in all eukaryotes. An enzymatically active complex was isolated from microsomal membranes from Saccharomyces cer evisiae, which is composed of four proteins: Wbp1p and Swp1p (previous ly found to be encoded by two essential genes necessary for N-glycosyl ation in vivo and in vitro) and two additional proteins with a molecul ar mass of 60/62 kDa and 34 kDa. The 60/62 component represents differ entially glycosylated forms of a protein that has sequence homology to ribophorin I. Wbp1p and Swp1p reveal homology to mammalian OST 48 and ribophorin II, respectively. Ribophorin I and II and OST 48 were rece ntly shown to be constituents of the mammalian transferase from dog pa ncreas. The data reveal a high conservation of the organization of thi s enzyme activity.