A NOVEL ADAPTER-RELATED PROTEIN COMPLEX

Coat proteins are required for the budding of the transport vesicles t hat mediate membrane traffic pathways, but for many pathways such prot eins have not yet been identified. We have raised antibodies against p 47, a homologue of the medium chains of the adaptor complexes of clath rin-coated vesicles (Pevsner, J., W. Volknandt, B.R. Wong, and R.H. Sc heller. 1994, Gene (Amst.). 146:279-283), to determine whether this pr otein might be a component of a new type of coat. p47 coimmunoprecipit ates with three other proteins: two unknown proteins of 160 and 25 kD, and beta-NAP, a homologue of the beta/beta'-adaptins, indicating that it is a subunit of an adaptor-like heterotetrameric complex. However, p47 is not enriched in preparations of clathrin-coated vesicles. Recr uitment of the p47-containing complex onto cell membranes is stimulate d by GTP gamma S and blocked by brefeldin A, indicating that, like oth er coat proteins, its membrane association is regulated by an ARF. The newly recruited complex is localized to non-clathrin-coated buds and vesicles associated with the TGN. Endogenous complex in primary cultur es of neuronal cells is also localized to the TGN, and in addition, so me complex is associated with the plasma membrane. These results indic ate that the complex is a component of a novel type of coat that facil itates the budding of vesicles from the TGN, possibly for transporting newly synthesized proteins to the plasma membrane.