Ribophorin I is an essential subunit of oligosaccharyltransferase (OST), which is also known as Dolichyl-diphosphooligosaccharide--protein glycosyltransferase, (EC:188.8.131.52). OST catalyzes 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. 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 Most family members are predicted to have a transmembrane helix at the C-terminus of this region.