Assembly factor that plays a role in the assembly of the respiratory chain supercomplexes (SCs) composed of ubiquinol-cytochrome c oxidoreductase (cytochrome b-c1 complex, complex III, CIII) and cytochrome c oxidase (complex IV, CIV). Involved in the recruitment of COX13 and RCF2 into cytochrome c oxidase. May also be required for late-stage assembly of the COX12 and COX13 subunits (PubMed:22342701, PubMed:22405070, PubMed:22310663). Required for the generation and maintenance of a normal proton motive force (PMF) across the inner mitochondrial membrane (IMM) by preventing proton leakage through an inactive population of CIV that accumulates when RCF1 and/or RCF2 proteins are absent (PubMed:30683696, PubMed:31591265). Associates with a subpopulation of the cytochrome bc1-cytochrome c oxidase supercomplexes (PubMed:19750512, PubMed:22342701, PubMed:22405070, PubMed:22310663). Associates in substoichiometric amounts with complex IV (PubMed:22310663). Interacts with COX3 (PubMed:22310663). Increases frequency of mitochondrial genome loss. Promotes reactive oxygen species (ROS) generation. Present with 1210 molecules/cell in log phase SD medium. Belongs to the AIM31 family.