Mitochondrial inner membrane insertase that mediates the insertion of both mitochondrion-encoded precursors and nuclear-encoded proteins from the matrix into the inner membrane. Links mitoribosomes with the inner membrane (PubMed:22904327). Forms pores capable of accommodating translocating protein segments (PubMed:22829595). Essential for the activity and assembly of cytochrome c oxidase (PubMed:22904327). Plays a central role in the translocation and export of the N-terminal part of the COX2 protein into the mitochondrial intermembrane space. Interacts with the large ribosome subunit of mitochondrial ribosome (PubMed:14657017, PubMed:22904327). Interacts directly with MRP20 (PubMed:14657017). Interacts with OXA1 (PubMed:25609543). The availability of nuclear- and mitochondrial-encoded substrates influences the inner- membrane distribution. Leads to reduced steady-state levels and activities of the mitochondrial ATP/ADP carrier protein AAC2. Present with 6550 molecules/cell in log phase SD medium. Belongs to the OXA1/ALB3/YidC family.