Primary structure of the smallest (6.4-kDa) subunit of human and bovine ubiquinol-cytochrome c reductase deduced from cDNA sequences.

Amino acid sequences of the smallest subunit of human and bovine ubiquinol-cytochrome c reductase were deduced from nucleotide sequence of recombinant cDNA clones isolated by screening the corresponding cDNA libraries. Both proteins were composed of 56 amino acids. They were 84% homologous to each other in the coding nucleotide sequences and 88% homologous in the amino acid sequences. Southern blot analysis with human DNA suggested the presence of a single gene coding for the protein. Northern blot of human mRNAs from different tissues confirmed the existence of a single species of transcript among the tissues but the human gene is highly expressed in bioenergetically active tissues like heart and skeletal muscle.