DAD1 Background Information
Membrane proteins of the endoplasmic reticulum (ER) may be localized by mechanisms that involve retention, retrieval, or a combination of both (1,2). ER localization information has been found in cytoplasmic, transmembrane, or luminal domains (2). Specific retrieval mechanisms have been identified for luminal ER proteins, which contain a KDEL domain, and for type I transmembrane proteins carrying a dilysine motif (2). The mammalian oligosaccharyltransferase (OST) is a protein complex that is composed of four rough ER-specific, type I transmembrane proteins: ribophorins I and II (RI and RII), OST48, and DAD1 (also designated defender against apoptotic death) (1,3,4). The ribophorins are integral membrane glycoproteins that localize exclusively to the rough endoplasmic reticulum (5,6). There is affinity between the cytoplasmically located N-terminal region of DAD1 and the short cytoplasmic tail of OST48 to place DAD1 firmly into the OST complex (3-5). The OST affects the cotranslational N-glycosylation of newly synthesized polypeptides (1).
