TRIMERIC G-PROTEINS REGULATE THE CYTOSOL-INDUCED REDISTRIBUTION OF GOLGI ENZYMES INTO THE ENDOPLASMIC-RETICULUM

Streptolysin O-permeabilized cells incubated with a high concentration (5-10 mg/ml) of cytosolic proteins and ATP-generating system exhibit redistribution into the endoplasmic reticulum (ER) of Golgi integral p roteins (mannosidase Il, galactosyltransferase, TGN 38), detected by i mmunofluorescence. In addition, mannosidase II is detected in the ER o f cells exposed to a high concentration of cytosolic proteins and proc essed for immunoelectron microscopy by immunoperoxidase. The redistrib ution process requires ATP and is not affected by previous microtubule depolymerization. Ultrastructural observations indicate that Golgi di sassembly occurs by budding of coated vesicles. This stage of the proc ess is inhibited by GTP gamma S, AlF(3-5), transducin beta gamma subun its, and mastoparan, indicating the involvement of trimeric G proteins . At a later stage, vesicles lose their coats acid fuse with the ER, T his part of the process does not occur in cells incubated at either 15 degrees C or 20 degrees C, or exposed to N-ethylmaleimide. In cells t reated with either cholera or pertussis toxin Golgi redistribution int o the ER shows a 50-fold lower requirement for cytosolic factors than in untreated cells. These data suggest a regulatory role for both as a nd al trimeric G proteins in the normal Golgi-ER retrograde transport taking place in intact cells.