Beta-COP, a 110 Kd Protein Associated with Non-clathrin-coated Vesicles and the Golgi Complex, Shows Homology to Beta-adaptin

We have cloned and sequenced beta-COP, a peripheral 110 kd Golgi membrane protein. beta-COP shows significant homology to beta-adaptin. It is present in a membrane-bound form and in a cytosolic complex of 13-14S, with a Stokes radius of approximately 10 nm and an estimated Mr of approximately 550,000. By immunofluorescence labeling, beta-COP is associated with the structures of the Golgi complex. Immunoelectron microscopy has localized beta-COP to non-clathrin-coated vesicles and cisternae of the Golgi complex. These coated vesicles accumulate in rat liver Golgi fractions treated with GTP gamma S and strongly label for beta-COP. Our data suggest that beta-COP is a component of a coat associated with vesicles and cisternae of the Golgi complex.