Coa1 links the Mss51 post-translational function to Cox1 cofactor insertion in cytochrome c oxidase assembly

The assembly of cytochrome c oxidase (CcO) in yeast mitochondria is shown to be dependent on a new assembly factor designated Coa1 that associates with the mitochondrial inner membrane. Translation of the mitochondrial-encoded subunits of CcO occurs normally in coa1 Delta cells, but these subunits fail to accumulate. The respiratory defect in coa1D cells is suppressed by highcopy MSS51, MDJ1 and COX10. Mss51 functions in Cox1 translation and elongation, whereas Cox10 participates in the biosynthesis of heme a, a key cofactor of CcO. Respiration in coa1D and shy1 Delta cells is enhanced when Mss51 and Cox10 are coexpressed. Shy1 has been implicated in formation of the heme a(3)-Cu-B site in Cox1. The interaction between Coa1 and Cox1, and the physical and genetic interactions between Coa1 and Mss51, Shy1 and Cox14 suggest that Coa1 coordinates the transition of newly synthesized Cox1 from the Mss51: Cox14 complex to the heme a cofactor insertion involving Shy1. coa1D cells also display a mitochondrial copper defect suggesting that Coa1 may have a direct link to copper metallation of CcO.