Required for protein transport to the vacuole. Involved in two vesicle trafficking steps to the prevacuolar compartment (PVC), regulating the docking of endosomes and Golgi vesicles to the PVC by interacting with PEP7/VAC1 on the PVC membrane and promoting SNARE complex formation. Alternates between an inactive form bound to GDP and an active form bound to GTP. Activated by the guanine nucleotide-exchange factor (GEF) VPS9 and inactivated by GTPase-activating proteins (GAPs) GYP1 and GYP3. Interacts in its active GTP-bound form with PEP7/VAC1. Present with 8759 molecules/cell in log phase SD medium. Belongs to the small GTPase superfamily. Rab family.