Complete mitochondrial genome of sea urchin: Mesocentrotus nudus (Strongylocentrotidae, Echinoida).

The complete nucleotide of mitochondrial DNA of a sea urchin Mesocentrotus nudus was determined for the first time. It is 15,709 bp in length, containing 2 rRNA, 22 tRNA and 13 protein-coding genes generally found in other echinoderm species. The gene order and structure of the genome are identical to those of other Strongylocentrotidae species. The genome was composed of 29.3% A, 23.4% C, 29.5% T and 17.8% G, showing a slight AT bias (58.8%). The G is the least used base and markedly lower at the third codon position (12.74%). Twelve of the 13 mitochondrial protein-coding genes use ATG as their start codon while the ATP8 gene starts with GTG. The control region is 125 bp in length and contains a G-stretch of 19 nucleotides, a typical DNA structure of the echinoid mitochondrial genomes.