Mitochondrial membrane insertase that mediates the cotranslational insertion of integral membrane proteins into the mitochondrial inner membrane (PubMed:17936786, PubMed:33602856, PubMed:7991568). Essential for the activity and assembly of cytochrome oxidase (PubMed:17936786, PubMed:7991568). Required for the correct biogenesis of ATP synthase and complex I in mitochondria (PubMed:17936786, PubMed:7991568).