Accessory component of the V0 complex of vacuolar(H+)-ATPase (V-ATPase), a multisubunit enzyme composed of a peripheral complex (V1) that hydrolyzes ATP and a membrane integral complex (V0) that translocates protons (PubMed:29526695). V-ATPase is responsible for acidifying and maintaining the pH of intracellular compartments (PubMed:29526695). Functions with VMA21 in assembly of the V0 complex (PubMed:18799613). V-ATPase is a heteromultimeric enzyme composed of a peripheral catalytic V1 complex (components A to H) attached to an integral membrane V0 proton pore complex (components: a, c, c', c'', d, e, f and VOA1) (PubMed:29526695). Interacts with VMA21 (PubMed:18799613). Associates with the assembling V0 complex (PubMed:18799613). Reduces association of VMA6 with the V-type proton ATPase (PubMed:29526695). Decreases VPH1 protein level (PubMed:29526695). Present with 12764 molecules/cell in log phase SD medium. Belongs to the VOA1 family.