ABSTRACT
By antibody screening of a rat liver and a rat heart cDNA library in lambda gt11 two clones coding for the liver- and heart-specific subunit VIa of rat cytochrome c oxidase were isolated. In the heart cDNA sequence a TAA stop codon was found in frame 18 bp 5' upstream of the first methionine codon, thus excluding a leader sequence for this protein. The two cDNAs contain the full-length coding region of two subunits. The amino acid sequences of the two subunits show only 50% homology, whereas 74% homology was found between rat heart and bovine heart subunit VIa. By Northern blot analysis it is shown that the gene for subunit VIa from heart is only expressed in heart and skeletal muscle, whereas that from liver is also expressed in kidney, brain, heart and weakly in muscle.
Subject(s)
DNA/genetics , Electron Transport Complex IV/genetics , Liver/enzymology , Myocardium/enzymology , Amino Acid Sequence , Animals , Base Sequence , Blotting, Northern , Cloning, Molecular , Codon/genetics , Molecular Sequence Data , Protein Sorting Signals/genetics , RNA/analysis , Rats , Sequence Homology, Nucleic AcidABSTRACT
A rat genomic library was screened with a cDNA probe coding for rat liver cytochrome c oxidase subunit VIc (COX-VIc). Out of 16 clones mapped, four inserts were different and did not overlap. Two inserts that gave strong hybridization signals were characterized by sequence analysis. These data show that we have cloned two different genes for rat COX-VIc. The rat COX-VIc-2 gene contains four exons and three introns. The 5' boundary of the first exon was mapped by primer extension experiments. The nucleotide sequence of the first three exons is identical to the sequence of the rat liver cDNA probe; thus, we can conclude that this gene is expressed in rat liver. The second gene (COX-VIc-1) is 88% homologous to the rat liver cDNA and contains an open reading frame of 228 nucleotides capable of coding for a full-length COX-VIc polypeptide of 76 amino acids. This predicted translation product is 79% homologous to the rat liver peptide. The absence of introns and other factors, such as the presence of a 13-bp direct repeat and a poly(A) addition signal, indicate that this locus is a processed gene which may have evolved from spliced mRNA intermediates.
