The first analysed archegoniate mitochondrial gene (COX3) exhibits extraordinary features

The first mitochondrial-encoded gene of an archegoniate has been identified, cloned and sequenced. The cytochrome oxidase III gene (cox3) of the moss Physcomitrella patens consists of a 618 bp open reading frame with high homology (around 72%) to known cox3 sequences of higher plants. Nevertheless, it is a quarter shorter than these. The cox3 gene of P. patens contains no introns and reveals a G + C-content of 41.3%. The region containing the cox3 gene exists as a single copy in the mitochondrial genome as shown by restriction mapping. In the 5' flanking sequence a putative ribosome binding site and a putative secondary structure were found. Two main transcripts of 2.4 kb and 2.6 kb were detected indicating a complex mitochondrial transcription pattern possibly due to co-transcription. Additional open reading frames were found downstream from, as well as upstream of, the cox3 gene. In Western blots a polyclonal cox3 antibody from yeast detected one single band with an apparent molecular weight of 22 kDa.