Required for assembly of cytochrome c oxidase (complex IV). With COX14, regulates negatively COX1 translation and is involved in MSS51 association with newly synthesized COX1. Component of 250-400 kDa complexes called cytochrome oxidase assembly intermediates or COA complexes composed at least COA3, COX14, COX5A, SHY1 and SSC1. Interacts with COX1 and MSS51. Present with 2530 molecules/cell in log phase SD medium. Belongs to the COA3 family.