Campbell N J, Barker S C
Department of Parasitology, University of Queensland, Brisbane, Australia.
Mol Biol Evol. 1999 Jun;16(6):732-40. doi: 10.1093/oxfordjournals.molbev.a026158.
We sequenced across all of the gene boundaries in the mitochondrial genome of the cattle tick, Boophilus microplus, to determine the arrangement of its genes. The mtDNA of B. microplus has a coding region, composed of tRNA(Glu) and 60 bp of the 3' end of ND1, that is repeated five times. Boophilus microplus is the first coelomate animal known to have more than two copies of a coding sequence. The mitochondrial genome of B. microplus has other unusual features, including (1) reduced T arms in tRNAs, (2) an AT bias in codon use, (3) two control regions that have evolved in concert, (4) three gene 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 ticks suggest strong selection for small genomes. Imprecise termination of replication beyond its origin, which can account for the evolution of tandem repeats 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 most plausible explanations for the evolution of these tandem repeats.
我们对微小牛蜱（Boophilus microplus）线粒体基因组中的所有基因边界进行了测序，以确定其基因排列。微小牛蜱的线粒体DNA有一个编码区，由tRNA（Glu）和ND1 3'端的60个碱基对组成，该编码区重复了五次。微小牛蜱是已知的第一种拥有超过两个编码序列拷贝的真体腔动物。微小牛蜱的线粒体基因组还有其他不寻常的特征，包括：（1）tRNA中的T臂缩短；（2）密码子使用偏向于AT；（3）两个协同进化的控制区；（4）三次基因重排；（5）tRNA（Gln）和tRNA（Phe）之间的一个茎环结构。微小牛蜱和其他蜱类较短的T臂及较小的控制区表明对小基因组有强烈的选择作用。复制在其起点之外的不精确终止，虽然可以解释其他线粒体基因组中编码区串联重复序列的进化，但无法解释微小牛蜱线粒体基因组中五倍重复序列的进化。相反，滑链错配或重组是这些串联重复序列进化的最合理的解释。
