The function of TCIRG1 (T cell immune regulator 1, ATPase H+ transporting V0 subunit a3, Ensembl gene identifier ENSG00000110719) is as follows. 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 (By similarity). V-ATPase is responsible for acidifying and maintaining the pH of intracellular compartments and in some cell types, is targeted to the plasma membrane, where it is responsible for acidifying the extracellular environment (By similarity). Seems to be directly involved in T-cell activation (PubMed:10329006). {ECO:0000250|UniProtKB:Q29466, ECO:0000250|UniProtKB:Q93050, ECO:0000269|PubMed:10329006}.