BETA'-COP, A NOVEL SUBUNIT OF COATOMER

Several lines of evidence favour the hypothesis that intracellular bio synthetic protein transport in eukaryotes is mediated by non-clathrin- coated vesicles (for a review see Rothman and Orci, 1992). The vesicle s have been isolated and a set of their surface proteins has been char acterized as coat proteins (COPs). These COPs exist in the cytosol as a preformed complex, the coatomer, which was prior to this study known to contain six subunits: four (alpha-, beta-, gamma- and delta-COP) w ith molecular weights between 160 and 58 kDa, and two additional prote ins of approximately 36 and 20 kDa, epsilon- and xi-COP. Here we descr ibe a novel subunit of the coatomer complex, beta'-COP. This subunit o ccurs in amounts stoichiometric to the established COPs both in the co atomer and in non-clathrin-coated vesicles and shows homology to the b eta-subunits of trimeric G proteins.