Subunit 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:8509410). V-ATPase is responsible for acidifying and maintaining the pH of intracellular compartments (PubMed:8509410). This subunit is a non-integral membrane component of the membrane pore domain and is required for proper assembly of the V0 sector (PubMed:8509410). Might be involved in the regulated assembly of V1 subunits onto the membrane sector or alternatively may prevent the passage of protons through V0 pores (PubMed:8509410). 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). Present with 1630 molecules/cell in log phase SD medium. Belongs to the V-ATPase V0D/AC39 subunit family.