Essential for vacuolar biogenesis, maturation and function. Involved in the sorting of vacuolar proteins from the Golgi apparatus and their targeting to the vacuole. Acts as component of the HOPS complex that acts during the docking stage of vacuole fusion. HOPS is an effector for the vacuolar Rab GTPase YPT7 and is required for vacuolar SNARE complex assembly. It remains bound to SNARE complexes after vacuole fusion. Component of the HOPS complex which is composed of PEP5, VPS16, PEP3, VPS33, VPS39 and VPS41. HOPS associates with phosphoinositides and the PX domain of VAM7. Interacts with IVY1 and VAM7. Present with 830 molecules/cell in log phase SD medium. Belongs to the STXBP/unc-18/SEC1 family.