Characterization of the complete mitochondrial genome of Bombyx mori strain H9 (Lepidoptera: Bombycidae).

The complete mitochondrial genome (mitogenome) of Bombyx mori strain H9 (Lepidoptera: Bombycidae) is 15,670base pairs (bp) in length, encoding 13 protein-coding genes (PCGs), two rRNA genes, 22 tRNA genes and a control region. The nucleotide composition of the genome is highly A+T biased, accounting for 81.31%, with a slightly positive AT skewness (0.059). The arrangement of 13 PCGs is similar to that of other sequenced lepidopterans. All the PCGs are initiated by ATN codons, except for the cytochrome c oxidase subunit 1 (cox1) gene, which is proposed by the TTAG sequence as observed in other lepidopterans. Unlike the other PCGs, the cox1 and cytochrome c oxidase subunit 2 (cox2) genes have incomplete stop codons consisting of just a T. All tRNAs have typical structures of insect mitochondrial tRNAs, which is different from other sequenced lepidopterans. The structure of A+T-rich region is similar to that of other sequenced lepidopterans, including non-repetitive sequences, the ATAGA binding domain, a 18bp poly-T stretch and a poly-A element upstream of transfer RNA M (trnM) gene. Phylogenetic analysis shows that the domesticated silkmoth B. mori originated from the Chinese Bombyx mandarina.