Inohira K, Hara T, Matsuura E T
Department of Biology, Ochanomizu University, Tokyo, Japan.
Mol Biol Evol. 1997 Aug;14(8):814-22. doi: 10.1093/oxfordjournals.molbev.a025822.
We have determined the nucleotide sequences of two regions within the A+T-rich region of mitochondrial DNA (mtDNA) in the siIII type of Drosophila simulans and the maI type of D. mauritiana. The sequences of the two regions in siIII and maI are almost identical. The sequences include elements corresponding to the type I and type II repeats elements and the T-stretches as reported in D. melanogaster; an approximately 340-bp region (A region) adjacent to the tRNA(Ile) gene includes a part of the type II repeat element, and an approximately 440-bp region (B region) includes a central portion of the A+T-rich region between the type I and type II repeat arrays. Each sequence of the two species was compared with those of D. melanogaster and D. yakuba. The sequences of the A region are relatively well conserved among the four species. The alignment of the two sequences of the B region with those of D. melanogaster and D. yakuba requires numerous insertions/deletions. For both regions, nucleotide differences between D. simulans or D. mauritiana and D. melanogaster are similar to those between the two and D. yakuba. The tendency is obvious in a subregion within the type II repeat element in the A region. These findings suggest that the rate of nucleotide substitution in the subregion is accelerated in the lineage leading to D. melanogaster. Loss of functional constraint in the stem-loop-forming sequence is proposed for this acceleration.
我们已经测定了拟暗果蝇（Drosophila simulans）的siIII型和毛里求斯果蝇（D. mauritiana）的maI型线粒体DNA（mtDNA）富含A+T区域内两个区域的核苷酸序列。siIII型和maI型中这两个区域的序列几乎相同。这些序列包含与黑腹果蝇（D. melanogaster）中报道的I型和II型重复元件以及T序列相对应的元件；与tRNA（Ile）基因相邻的一个约340 bp的区域（A区域）包含II型重复元件的一部分，一个约440 bp的区域（B区域）包含I型和II型重复阵列之间富含A+T区域的中心部分。将这两个物种的每个序列与黑腹果蝇和雅库布果蝇（D. yakuba）的序列进行了比较。A区域的序列在这四个物种中相对保守。B区域的两个序列与黑腹果蝇和雅库布果蝇的序列比对需要大量的插入/缺失。对于这两个区域，拟暗果蝇或毛里求斯果蝇与黑腹果蝇之间的核苷酸差异与它们和雅库布果蝇之间的差异相似。这种趋势在A区域II型重复元件内的一个子区域中很明显。这些发现表明，在导致黑腹果蝇的谱系中，该子区域的核苷酸替换率加快。有人提出，这种加速是由于茎环形成序列中功能限制的丧失。
