SNARE complex protein that binds to cis-SNARE complexes on membranes and is required for vesicular transport between the endoplasmic reticulum and the Golgi apparatus and for homotypic vacuole fusion. During the priming step of membrane fusion, is released from cis-SNARE complexes by SEC18 to establish a pool of unpaired SNAREs, which are required for interactions in trans during docking and fusion steps. Can displace HOPS from SNARE complexes, which may be a prerequisite for trans-SNARE complex disassembly and subsequent rounds of priming, docking and fusion. Binds to vacuolar cis-SNARE complexes composed of the v-SNAREs NYV1, VTI1 and YKT6, and the t-SNAREs VAM3 and VAM7. Interacts with SEC18. Belongs to the SNAP family.