Isolation and characterization of a cDNA clone for bovine cytochrome c oxidase subunit IV.

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Abstract
A c [complementary] DNA clone was isolated for the precursor to subunit IV of bovine cytochrome c oxidase (ferrocytochrome c:oxygen oxidoreductase, EC 1.9.3.1). A cDNA library was constructed from poly(A)+ RNA of adult beef liver by insertion of cDNA into the plasmid vector pBR322. Transformants were screened by colony hybridization with 2 mixtures of [32P]-labeled synthetic oligodeoxyribonucleotides. There were 20,000 transformants screened with a mixture of heptadecamers complementary to all 16 possible sequences encoding amino acids 98-103 and 2 cDNA clones were obtained encoding subunit IV amino acid sequences. The DNA sequence of the larger (416 base-pair) insert was determined, which contains the coding sequence for amino acids 1-107 of the mature protein and an NH2-terminal extension (presequence). The deduced amino acid sequence of the mature protein is identical with the previously protein sequence; the sequence of the NH2-terminal extension contains a potential initiator methionine at amino acid -22 from the NH2-terminus of the processed protein. The presequence is quite basic and contains several Arg, including one at the processing site. No hydrophobic region analogs to that found in bacterial and eukaryotic signal peptides is present, but there are homologies with other mitochondrial protein presequences, which may include a common signal for their destination and processing.