Yeast Kex1p is a Golgi-associated membrane protein: deletions in a cytoplasmic targeting domain result in mislocalization to the vacuolar membrane

Kexlp is a glycoprotein which receives Asn-linked glycosylation in a multistep process (Cooper and Bussey, 1989) . The initial event occurs in the ER where core oligosaccharides are attached to the protein. The observed difference in molecular mass of ~ 3-4 kD between Kexlp labeled for 10 min and that of Kexlp produced in tunicamycintreated cells suggests that two of the three predicted lumenal Asn acceptor residues are glycosylated. The Ash-linked core oligosaccharides undergo a modification in a post-ER compartment that increases the mass of Kexlp by 1-2 kD, demonstrating that Kexlp does not receive an extensive outer chain (Cooper and Bussey, 1989) . Such a modification was reduced in a secl mutant which blocks intra-Golgi transport, and was unaffected in a secl mutant that prevents secretory vesicle fusion with the plasma membrane (Novick et al., 1981; Cooper and Bussey, 1989) .