Working model for vacuole to vacuole fusion and its regulation. Abbreviations: Sec17p (17), Sec18p (18), Nyv1p, Ykt6p, and Vti1 (v [individually] or v3), Vam3p (t), Vam7p (s), pro-alkaline phosphatase (Pro-ALP), alkaline phosphatase (ALP), GTPγs, guanosine 5′-[γ-thio]triphosphate. ∗ on the t-SNARE indicates the activated state of the protein after priming. Inhibitors are written in italics. Arrows indicate activators, bars indicate inhibitors. See text for details.