INTERACTION OF SEC4 WITH GDI PROTEINS FROM BOVINE BRAIN, DROSOPHILA-MELANOGASTER AND SACCHAROMYCES-CEREVISIAE - CONSERVATION OF GDI MEMBRANE DISSOCIATION ACTIVITY

Rab GDP dissociation inhibitor (Rab GDI), will induce the dissociation of GDP-bound rab3A from synaptic membranes and will inhibit GDP disso ciation from Sec4, a member of the Rab subgroup of the Ras GTPase supe rfamily which is required for exocytosis in Saccharomyces cerevisiae. We report that Rab GDI releases GDP-bound Sec4 from yeast membranes. d GDI, a Drosophila homologue can similarly inhibit GDP dissociation fro m Sec4 and release GDP-bound Sec4 from yeast membranes. An activity pa rtially purified from yeast cytosol dissociates GDP-bound Sec4 from ye ast membranes, suggesting that yeast also possess a GDI protein that f unctions to recycle Sec4 from its target membrane.