TRIMERIC G-PROTEIN ALPHA-SUBUNITS OF THE GS AND GI FAMILIES LOCALIZEDAT THE GOLGI MEMBRANE

The occurrence of individual G proteins within Golgi membranes from li ver and from adrenal medulla were analyzed by Western blotting. Two sp lice variants of G alpha s and also G alpha i-3 were found in both tis sues. Additionally, G alpha i-2, its 43-kDa splice variant and G alpha o were strongly labeled in Golgi of adrenal medulla. Golgi preparatio ns of liver contained comparable quantities of G alpha i-2 and a secon d variant of 46 kDa, but no G alpha o was detected. Immunoelectron mic roscopic studies of the above Golgi preparations showed that both C al pha i-2 and G alpha i-3 are localized at multivesicular structures ide ntified as Golgi complexes. The occurrence of two stimulatory G protei ns (G alpha s-S and G alpha s-L) and three or four alpha subunits of t he Gi/Go type as components of the Golgi membrane support the notion t hat formation of different vesicle types might be regulated by individ ual stimulatory and inhibitory G proteins. (C) 1995 Academic Press, In c.