ACTION OF BREFELDIN-A BLOCKED BY ACTIVATION OF A PERTUSSIS-TOXIN-SENSITIVE G-PROTEIN

IN many mammalian cells brefeldin A interferes with mechanisms that keep the Golgi apparatus separate from the endoplasmic reticulum 1-8. The earliest effect of brefeldin A is release of the coat protein beta-COP from the Golgi 9-11. This release is blocked by pretreatment with GTP-gamma-S or AlF4- (ref. 12). The AlF4- ion activates heterotrimeric C proteins 13 but not proteins of the ras superfamily 14, suggesting that a heterotrimeric G protein might control membrane transfer from the endoplasmic reticulum to the Golgi. We report here that mastoparan, a peptide that activates heterotrimeric G proteins 15,16, promotes binding of beta-COP to Golgi membranes in vitro and antagonizes the effect of brefeldin A on beta-COP in perforated cells and on isolated Golgi membranes. This inhibition is greatly diminished if cells are pretreated with pertussis toxin before perforation., Thus, a heterotrimeric G protein of the G(i)/G(o) subfamily regulates association of coat components with Golgi membranes.