TUBULAR MEMBRANE INVAGINATIONS COATED BY DYNAMIN RINGS ARE INDUCED BYGTP-GAMMA-S IN NERVE-TERMINALS

THE mechanisms through which synaptic vesicle membranes are reinternal ized after exocytosis remain a matter of debate(1-5). Because several vesicular transport steps require GTP hydrolysis(6-9), GTP-gamma S may help identify intermediates in synaptic vesicle recycling. In GTP-gam ma S-treated nerve terminals, we observed tubular invaginations of the plasmalemma that were often, but not always, capped by a clathrin-coa ted bud, Strikingly, the walls of these tubules were decorated by tran sverse electron-dense rings that were morphologically similar to struc tures formed by dynamin around tubular templates(10,11). Dynamin is a GTPase implicated in synaptic vesicle endocytosis(12-14) and here we s how that the wails of these membranous tubules, but not their distal e nds, were positive for dynamin immunoreactivity, These findings demons trate that dynamin and clathrin act at different sites in the formatio n of endocytic vesicles, They strongly support a role for dynamin in t he fission reaction and suggest that stabilization of the GTP-bound co nformation of dynamin leads to tubule formation by progressive elongat ion of the vesicle stalk.