title: Initiation codons in mammalian mitochondria: differences in genetic code in the organelle.
abstract: The bovine mitochondrial gene products ND2 and ND4, components of NADH dehydrogenase, have been purified from a chloroform/methanol extract of mitochondrial membranes, and the human mitochondrial gene products ND2 and cytochrome b have been obtained by similar procedures. They have been identified by comparison of their amino-terminal protein sequences with those predicted from DNA sequences of bovine and human mitochondrial DNA. All of the proteins have methionine as their amino-terminal residue. In bovine ND2, this residue is encoded by the "universal" isoleucine codon AUA, and the sequences of human cytochrome b and bovine ND2 demonstrate that AUA also encodes methionine in the elongation step of mitochondrial protein synthesis. In human ND2, the amino-terminal methionine is encoded by AUU, which, as in the "universal" genetic code, is also used as an isoleucine codon in elongation. Thus, AUU has a dual coding function which is dependent upon its context.
authors.affiliation: MRC Laboratory of Molecular Biology, Cambridge, U.K.
authors.forename: I M
authors.initials: IM
authors.lastname: Fearnley
authors.forename: J E
authors.initials: JE
authors.lastname: Walker
mesh_terms: D000251:Adenosine Triphosphatases / Q000235:genetics* / Q000302:isolation & purification; D000596:Amino Acids / Q000032:analysis; D000818:Animals; D002417:Cattle; D003062:Codon; D003579:Cytochrome Reductases / Q000235:genetics*; D003573:Cytochrome b Group / Q000235:genetics* / Q000302:isolation & purification; D004272:DNA, Mitochondrial / Q000235:genetics*; D005260:Female; D005796:Genes; D006801:Humans; D046911:Macromolecular Substances; D008928:Mitochondria / Q000201:enzymology*; D008929:Mitochondria, Heart / Q000201:enzymology*; D008970:Molecular Weight; D009245:NADH Dehydrogenase / Q000235:genetics* / Q000302:isolation & purification; D010920:Placenta / Q000201:enzymology; D012333:RNA, Messenger; D013367:Submitochondrial Particles / Q000201:enzymology
chemical_list: D000596:Amino Acids; D003062:Codon; D003573:Cytochrome b Group; D004272:DNA, Mitochondrial; D046911:Macromolecular Substances; D012333:RNA, Messenger; D003579:Cytochrome Reductases; D009245:NADH Dehydrogenase; D000251:Adenosine Triphosphatases