The novel mitochondrial gene arrangement of the cattle tick, Boophilus microplus: Fivefold tandem repetition of a coding region

We sequenced across all of the gene boundaries in the mitochondrial genome of the cattle tick, Boophilus microplus, to determine the arrangement of it s genes. The mtDNA of B. microplus has a coding region, composed of tRNA(Gl u) and 60 bp of the 3' end of ND1, that is repeated five times. Boophilus m icroplus is the first coelomate animal known to have more than two copies o f a coding sequence. The mitochondrial genome of B, microplus has other unu sual features, including (1) reduced T arms in tRNAs, (2) an AT bias in cod on use, (3) two control regions that have evolved in concert, (4) three gen e rearrangements, and (5) a stem-loop between tRNA(Gln) and tRNA(Phe). The short T arms and small control regions (CRs) of B. microplus and other tick s suggest strong selection for small genomes. Imprecise termination of repl ication beyond its origin, which can account for the evolution of tandem re peats of coding regions in other mitochondrial genomes, cannot explain the evolution of the fivefold repeated sequence in the mitochondrial genome of B. microplus. Instead, slipped-strand mispairing or recombination are the m ost plausible explanations for the evolution of these tandem repeats.