Genetic interaction between shibire and comatose mutations in Drosophila suggest a role for snap-receptor complex assembly and disassembly for maintenance of synaptic vesicle cycling.

NSF is an ATPase required for the fusion of secretory vesicles with plasma membrane. Conditional comatose (Drosophila homolog of N-ethylmaleimide sensitive fusion factor (NSF)) mutations in Drosophila block synaptic transmission at restrictive temperature. Current models hold that NSF-mediated dissociation of SNARE (SNAp REceptor) complexes on mature synaptic vesicles primes them for exocytic release. Paralysis in comt mutants thus reflects defective exocytosis due to buildup of unresolved SNARE complexes. Here, we analyze effects of blocking synaptic vesicle recycling on behavioral, physiological and biochemical phenotypes of comt. Behavioral recovery of comt animals and recovery of comt synapses, as assayed by electroretinograms, after exposure to high temperature is faster if synaptic vesicle recycling is simultaneously blocked using shi(ts) mutants. Concurrently, 7S complex buildup in comt shi double mutants is substantially lower than in comt mutants alone. In addition, we find that 7S complexes can form on presynaptic plasma membrane if NSF is inhibited after synaptic-vesicle depletion. Thus, our experiments demonstrate a need for continuous NSF activity required not only for dissociating cis-SNARE complexes on plasma membrane after exocytosis, but also for maintaining these cis-SNARE complexes in a dissociated state.