Structural organization and evolution of the liver isoform gene for bovine cytochrome c oxidase subunit VIIa.
Subunit VIIa of mammalian cytochrome c oxidase is one of three nuclear-encoded subunits that exhibit isoforms, existing predominantly as an H-form in cardiac and skeletal muscle tissues and as an L-form in others. We have isolated and characterized the L-isoform gene (COX7aL). It is 5.4 kb long, consists of four exons, and is located at a CpG island. Sp1 sites and an NRF1 site are located in an approximately 100-bp region immediately upstream of the gene. Comparison of the sequence and organization with the previously described H-isoform gene shows identical intron-exon organizations, with the first intron of both isoform genes splitting the presequence coding region almost identically. These results suggest that the isoform genes arose by duplication from a common ancestor prior to the mammalian radiation and that the ancestor already contained the presequences. In addition, four processed pseudogenes of the L-type have been isolated and characterized, one of which (COX7aLP1) contains no deletions, insertions, or frame-shifts and can encode a precursor protein of 83 amino acids. Construction of a phylogenetic tree employing extant COX7aL cDNA and bovine pseudogene sequences suggests that the expressed bovine gene and COX7aLP1 arose from a gene duplication event 4.6-6.8 Mya.
Seelan
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RS
Department of Molecular Biology and Genetics, Wayne State University School of Medicine, Detroit, Michigan 48201.
Grossman
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LI
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D005075:Biological Evolution; D002417:Cattle / Q000235:genetics*; D017931:DNA Primers; D003576:Electron Transport Complex IV / Q000235:genetics*; D005091:Exons; D015971:Gene Expression Regulation, Enzymologic; D006801:Humans; D007438:Introns; D007527:Isoenzymes / Q000235:genetics*; D008099:Liver / Q000201:enzymology*; D046911:Macromolecular Substances; D008969:Molecular Sequence Data; D009132:Muscles / Q000201:enzymology; D009206:Myocardium / Q000201:enzymology; D010802:Phylogeny; D016133:Polymerase Chain Reaction; D011544:Pseudogenes; D051381:Rats; D015183:Restriction Mapping; D017386:Sequence Homology, Amino Acid
D017931:DNA Primers; D007527:Isoenzymes; D046911:Macromolecular Substances; D003576:Electron Transport Complex IV