Required for vesicle-mediated transport. Catalyzes the fusion of transport vesicles within the Golgi cisternae. Is also required for transport from the endoplasmic reticulum to the Golgi stack. Seems to function as a fusion protein required for the delivery of cargo proteins to all compartments of the Golgi stack independent of vesicle origin (By similarity). ATP + H2O = ADP + H(+) + phosphate Binds 1 Mg(2+) ion per subunit. Homohexamer. Nervous system and secretory tissues. The highest levels are detected in embryos before and during cellularization. After onset of gastrulation the highest levels of expression appear in embryonic regions that give rise to endodermal and ectodermal tissues including the midgut and hindgut. Belongs to the AAA ATPase family. It is uncertain whether Met-1 or Met-9 is the initiator. Truncated N-terminus.