Has a role in the formation of the multivesicular body (MVB). Required for the sorting of lipids to form intralumenal vesicles and for fluid-phase transport to the vacuole. Required for sorting the plasma membrane proteins STE2 and STE3 into the MVB. Acts a cofactor of VSP4, promotes the oligomerization of VPS4 and stimulates its ATPase activity by 6- to 8-fold. Homodimer (in cytoplasm). Interacts with VPS4; the interaction requires the dimeric structure of VTA1; 6 homodimers of VTA1 appear to associate with the dodecameric VSP4 complex; the interaction is ADP-dependent. Interacts with SNF7; the interaction requires DID2. Interacts with DID2. Interacts with VPS60; the interaction occurs at he endosomal membrane. Present with 4400 molecules/cell in log phase SD medium. Belongs to the VTA1 family.