N-ethylmaleimide sensitive fusion protein (originally termed N-ethylmaleimide sensitive factor, hence the acronym NSF) is the name of a protein that is critically involved in the release of neurotransmitter at the neuronal synapse. The name was given to the protein by James Rothman and colleagues at Princeton University, as they identified NSF by the observation that it was inactivated by treatment with N-ethylmaleimide. NSF is an ATPase whose activity is thought to drive the fusion of the synaptic vesicle with the presynaptic plasma membrane at the synapse, resulting in release of the contents of the vesicle into the synaptic cleft.