Scaffold protein that participates in the c-ring assembly of mitochondrial ATP synthase (F(1)F(0) ATP synthase or complex V) by facilitating the membrane insertion and oligomer formation of the subunit c/ATP5MC1 through its interaction (By similarity). Therefore, participates in the early stage of mitochondrial ATP synthase biogenesis and also protects subunit c/ATP5MC1 against intramitochondrial proteolysis (PubMed:31652072, PubMed:28173120). In addition, binds the mitochondrial proton-transporting ATP synthase complexes I and may play a role in the stability of its membrane-bound subassemblies (By similarity). Homooligomer. Interacts (homooligomer form) with ATP5MC1; this interaction facilitates the oligomer formation of subunit c/ATP5MC1 (c-ring) and the c-ring membrane insertion and also protects ATP5MC1 against intramitochondrial proteolysis. Interacts with the core subunits TMEM126B, NDUFAF1, ECSIT and ACAD9 of the MCIA complex. Interacts with ATP5MC3, TMEM242 AND TIMMDC1. Mostly located within the inner cristae membrane. Higher expressed in the heart than in the liver (at protein level). Homozygous knockout mice for Tmem70 are embryonically lethal at about 9.5 days post coitum and exhibit profound growth retardation (PubMed:28173120). Embryos exhibit delayed development of the cardiovascular system and a disturbed heart mitochondrial ultrastructure, with concentric or irregular cristae structures (PubMed:28173120). Belongs to the TMEM70 family.