Mitochondrial gene order is not conserved in arthropods: prostriate and metastriate tick mitochondrial genomes

The entire mitochondrial genome was sequenced in a prostriate tick, Ixodeshexagonus, and a metastriate tick, Rhipicephalus sanguineus. Both genomesencode 22 tRNAs, 13 proteins, and two ribosomal RNAs. Prostriate ticks arebasal members of Ixodidae and have the same gene order as Limuluspolyphemus. In contrast, in R. sanguineus, a block of genes encoding NADHdehydrogenase subunit 1 (ND1), tRNA(Leu)(UUR), tRNA(Leu)(CUN), 16S rDNA,tRNA(Val), 12S rDNA, the control region, and the tRNA(Ile) and tRNA(Gln)have translocated to a position between the tRNA(Glu) and tRNA(Phe) genes.The tRNA(Cys) gene has translocated between the control region and thetRNA(Met) gene, and the tRNA(Leu)(CUN) gene has translocated between thetRNA(Ser)(UCN) gene and the control region. Furthermore, the control regionis duplicated, and both copies undergo concerted evolution. Primers thatflank these rearrangements confirm that this gene order is conserved in allmetastriate ticks examined. Correspondence analysis of amino acid and codonuse in the two ticks and in nine other arthropod mitochondrial genomesindicate a strong bias in R. sanguineus towards amino acids encoded byAT-rich codons.