Ribophorin I is an essential subunit of oligosaccharyltransferase (OST), which is also known as Dolichyl-diphosphooligosaccharide--protein glycosyltransferase, (EC:2.4.1.119). OST catalyses the transfer of an oligosaccharide from dolichol pyrophosphate to selected asparagine residues of nascent polypeptides as they are translocated into the lumen of the rough endoplasmic reticulum. Ribophorin I and OST48 are though to be responsible for OST catalytic activity [1]. Both yeast and mammalian proteins are glycosylated but the sites are not conserved. Glycosylation may contribute towards general solubility but is unlikely to be involved in a specific biochemical function [2] Most family members are predicted to have a transmembrane helix at the C terminus of this region.

1: The oligosaccharyltransferase complex from pig liver: cDNA cloning, expression and functional characterisation. Hardt B, Aparicio R, Bause E; Glycoconj J 2000;17:767-779. PMID:11443278

2: The essential yeast NLT1 gene encodes the 64 kDa glycoprotein subunit of the oligosaccharyl transferase. Pathak R, Parker CS, Imperiali B; FEBS Lett 1995;362:229-234. PMID:7720878