Complex III (cytochrome bc1) is a protein complex of the mitochondrial inner membrane that transfers electrons from ubiquinol to cytochrome c. UQCC1 and UQCC2 are complex III assembly factors participating in cytochrome b biogenesis [].
This family represents mitochondrial respiratory chain complex III (or cytochrome b-c1 complex) assembly factors, including cytochrome B pre-mRNA-processing protein 6 (Cbp6) from yeast and its human orthologue Ubiquinol-Cytochrome c Reductase Complex Assembly Factor 2 (UQCC2) [, ]. These proteins have diverged significantly among eukaryotes and UQCC2/Cbp6 have an overall low amino acid conservation []. UQCC2 interacts with UQCC1, the human orthologue of the Cbp6 binding partner Cbp3, to form a complex necessary for cytochrome b biogenesis []. Cbp3-Cbp6 complex interacts with mitochondrial ribosomes for efficient translation of cytochrome b transcript and it also interacts with newly synthesized cytochrome b to assist its correct assembly []. These proteins contain a LRY-like N-terminal sequence being related to the LYR superfamily of proteins, which function as subunits or assembly factors for respiratory complexes I, II, III, and V [].
