TEMPERATURE-SENSITIVE PARALYTIC MUTATIONS DEMONSTRATE THAT SYNAPTIC EXOCYTOSIS REQUIRES SNARE COMPLEX ASSEMBLY AND DISASSEMBLY

The neuronal SNARE complex is formed via the interaction of synaptobre vin with syntaxin and SNAP-25. Purified SNARE proteins assemble sponta neously, while disassembly requires the ATPase NSF. cycles of assembly and disassembly have been proposed to drive lipid bilayer fusion. How ever, this hypothesis remains to be tested in vivo. We have isolated a Drosophila temperature-sensitive paralytic mutation in syntaxin that rapidly blocks synaptic transmission at nonpermissive temperatures. Th is paralytic mutation specifically and selectively decreases binding t o synaptobrevin and abolishes assembly of the 7S SNARE complex. Temper ature-sensitive paralytic mutations in NSF (comatose) also block synap tic transmission, but over a much slower time course and with the accu mulation of syntaxin and SNARE complexes on synaptic vesicles. These r esults provide in vivo evidence that cycles of assembly and disassembl y of SNARE complexes drive membrane trafficking at synapses.