Proteins needed for vesicle budding from the golgi complex are also required for the docking step of homotypic vacuole fusion

Vam2p/Vps41p is known to be required for transport vesicles with vacuolar c argo to bud from the Golgi, Like other VAM-encoded proteins, which are need ed for homotypic vacuole fusion, we now report that Vam2p and its associate d protein Vam6p/Vps39p are needed on each vacuole partner for homotypic fus ion. In vitro vacuole fusion occurs in successive steps of priming, docking , and membrane fusion. While priming does not require Vam2p or Vam6p, the f unctions of these two proteins cannot be fulfilled until priming has occurr ed, and each is required for the docking reaction which culminates in trans -SNARE pairing. Consistent with their dual function in Golgi vesicle buddin g and homotypic fusion of vacuoles, approximately half of the Vam2p and Vam 6p of the cell are recovered from cell lysates with purified vacuoles.