Sequence analysis of the mitochondrial genome of Sarcophyton glaucum: Conserved gene order among octocorals

The nucleotide sequence for an 11,715-bp segment of the mitochondrial genom e of the octocoral Sarcophyton glaucum is presented, completing the analysi s of the entire genome for this anthozoan member of the phylum Cnidaria. Th e genome contained the same 13 protein-coding and 2 ribosomal RNA genes as in other animals. However, it also included an unusual mismatch repair gene homologue reported previously and codes for only a single tRNA gene. Inter mediate in length compared to two other cnidarians (17,443 and 18,911 bp), this organellar genome contained the smallest amount of noncoding DNA (428, compared to 1283 and 781 nt, respectively), making it the most compact one found for the phylum to date. The mitochondrial genes of S. glaucum exhibi ted an identical arrangement to that found in another octocoral, Renilla ko likeri, with five protein-coding genes in the same order as has been found in insect and vertebrate mitochondrial genomes. Although gene order appears to be highly conserved among octocorals, compared to the hexacoral, Metrid ium senile, few similarities were found. Like other metazoan mitochoadrial genomes, the A + T composition was elevated and a general bias against codo ns ending in G or C was observed. However, an exception to this was the inf requent use of TGA compared to TGG to code for tryptophan. This divergent c odon bias is unusual but appears to be a conserved feature among two rather distantly related anthozoans.