BINDING OF COATOMER TO GOLGI MEMBRANES REQUIRES ADP-RIBOSYLATION FACTOR

Coatomer, a complex of seven proteins, appears to be the precursor of the coat structure of non-clathrin-coated Golgi-derived vesicles. Anot her component of this vesicle coat is the cytosolic protein ADP-ribosy lation factor (ARF). Like coatomer, ARF appears to reversibly associat e with Golgi membranes. We now report that ARF is required for coatome r binding to Golgi membranes and that myristoylated, but not non-myris toylated, ARF is the required species. We utilize an antibody directed against the beta-subunit of coatomer (beta-COP) to follow coatomer bi nding. ARF and beta-COP bind stoichiometrically to Golgi membranes. AR F-dependent beta-COP binding requires a membrane-associated protein, i s saturable, and is enhanced in the presence of stable GTP analogues l ike guanosine 5'-O-(3-thiotriphosphate) (GTPgammaS). ARF and beta-COP bind sequentially to Golgi membranes, since beta-COP can be bound to r eisolated membranes that had been previously incubated with ARF and GT PgammaS. We conclude that membrane-bound ARF confers to Golgi membrane s all of the requirements for specific beta-COP binding.