An NSF function distinct from ATPase-dependent SNARE disassembly is essential for Golgi membrane fusion

The precise biochemical role of N-ethylmaleimide-sensitive factor (NSF) in membrane fusion mediated by SNARE proteins is unclear. To provide further i nsight into the function of NSF, we have introduced a mutation into mammali an NSF that, in Drosophila dNSF-1, leads to temperature-sensitive neuropara lysis. This mutation is like the comatose mutation and renders the mammalia n NSF temperature sensitive for fusion of postmitotic Golgi vesicles and tu bules into intact cisternae. Unexpectedly, at the temperature that is permi ssive for membrane fusion, this mutant NSF binds to, but cannot disassemble , SNARE complexes and exhibits almost no ATPase activity. A well-characteri zed NSF mutant containing an inactivating point mutation in the catalytic s ite of its ATPase domain is equally active in the Golgi-reassembly assay. T hese data indicate that the need for NSF during postmitotic Golgi membrane fusion may be distinct from its ATPase-dependent ability to break up SNARE pairs.