Results

Background An in vitro assay has been devised (Balch et al., 1984a) that measures the transport of the vesicular stomatitis virus-encoded glycoprotein (VSV-G) from the cis cisternae of Golgi stacks in fractions prepared from a mutant Chinese hamster ovary (CHO) cell line (defective in N-acetylglucosaminyl [GlcNAc] transferase 1) to the medial cisternae of wild-type CHO Golgi stacks; the addition of tritiated GlcNAc from its sugar nucleotide donor marks the arrival of VSV-G at the acceptor compartment and serves as a quantitative measure of the entire transport reaction. Analysis of kinetic intermediates formed during the in vitro transport pathway has revealed several sequential stages in the maturation of a transport vesicle prior to fusion (Figure 1; Balch et al., 1984b; Wattenberg et al., 1988; Malhotra et al., 1988; Orci et al., 1989). Inhibition of transport with the nucleotide analog GTPyS blocks the maturation of vesicles early in the pathway, resulting in an accumulation of coated vesicles that have transferred from donor to