Role of the Rab3A GTPase in regulated secretion from neuroendocrine cells.

Regulated secretion is a complex process that involves scores of distinct proteins. These proteins must assemble into machines that organize vesicle docking, membrane fusion, and recovery of vesicle components. Rab3A, a member of the Ras superfamily of GTPases, associates with secretory granule membranes of neuroendocrine cells, and mutants of Rab3A can inhibit exocytosis. A model is proposed in which Rab3A controls the assembly and disassembly of a docking complex that inhibits membrane fusion until an external signal triggers release of the Rab3A from the complex.