ABSTRACT
The mitochondrial cox2 gene has been sequenced from radish (Raphanus sativus L.). The gene is interrupted by a 1346-bp group-II intron and contains an ACG codon as the predicted translation initiation site. Analysis of cox2 cDNAs indicates that the ACG codon is not converted to an AUG codon in the mRNA, although 15 other RNA editing sites were identified. The cox2 gene from Raphanus raphanistrum, and other varieties of R. sativus, also contain an ACG as the predicted start codon; plants in the closely related genus, Brassica, do not. Western-blot analyses indicate that cox2 proteins in radish mitochondria are the same size as those found in Brassica mitochondria and different from cox2 proteins in plants where cox2 is nuclear-encoded. This finding, along with the observation that cox2 sequences are not present in the nuclear genome of radish, suggests that ACG is utilized as the radish cox2 initiation codon.