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

Abstract

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.