REGULATION OF ASSOCIATION OF A 58-KDA PERIPHERAL MEMBRANE-PROTEIN (58K) WITH THE GOLGI-APPARATUS - ITS MEMBRANE-BINDING PROPERTIES RELATED TO BUT DISTINCT FROM THOSE OF COP-I COAT PROTEINS

A 58-kDa membrane protein (58K) is a peripherally Golgi-associated pro tein that is capable of binding microtubules in vitro. Since microtubu les and their associated proteins play important roles in the organiza tion and dynamics of membrane-bounded organelles, we analyzed the beha vior of 58K when cells were treated with reagents that are known to af fect the Golgi morphology and the membrane binding of peripheral Golgi proteins. The 58K bound to Golgi membranes in an ATP-independent mann er, and was not associated with the Golgi tubules induced by treatment of cells with brefeldin A. These data indicate that, unlike kinesin w hich is an ATP-dependent molecular motor along microtubules, 58K is no t directly involved in the formation of Golgi tubules. Upon treatment of cells with ATP-depletion reagents and with combinations of brefeldi n A and other reagents, the Golgi disintegration appeared to be couple d with dissociation of 58K from Golgi membranes. By contrast, the Golg i disintegration was not always coupled with dissociation of beta-COP, component of the COP I coat protein complex, membrane association of which has been proposed to suppress the Golgi tubulation. These data s uggest a possibility that membrane association of 58K, rather than tha t of the COP I coat, plays some role in maintenance of the integral Go lgi structure.