TGA-Termination codon in the apocytochrome b gene from Oenothera mitochondria

Summary The apocytochrome b gene in the mitochondrial genome of Oenothera contains 1,185 base pairs (bp) in uninterrupted sequence. Comparison with the maize sequence indicates firstly that at the 5 end of the gene an additional triplet, coding for alanine, is inserted immediately behind the initiator ATG. Secondly the carboxy-terminus of the polypeptide is extended by five amino acids. The only in-frame termination codon for the Oenothera gene is a TGA triplet 15 nucleotides downstream from the maize TAG termination, which corresponds to a GAG codon in Oenothera. The plant mitochondria) tryptophan codon CGG and TGG appear to be interchangable although a bias for TGG is observed in this gene (12:1). At position 718–720 in the Oenothera nucleotide sequence TGG is found where a CGG occurs in maize, and nucleotide 361 in Oenothera gene is a T, generating a TGG codon where in maize a CGG codon is found.