McKnight M L, Shaffer H B
Section of Evolution and Ecology, University of California, Davis 95616, USA.
Mol Biol Evol. 1997 Nov;14(11):1167-76. doi: 10.1093/oxfordjournals.molbev.a025726.
We report the presence, in the mitochondrial DNA (mtDNA) of all of the sexual species of the salamander family Ambystomatidae, of a shared 240-bp intergenic spacer between tRNAThr and tRNAPro. We place the intergenic spacer in context by presenting the sequence of 1,746 bp of mtDNA from Ambystoma tigrinum tigrinum, describe the nucleotide composition of the intergenic spacer in all of the species of Ambystomatidae, and compare it to other coding and noncoding regions of Ambystoma and several other vertebrate mtDNAs. The nucleotide substitution rate of the intergenic spacer is approximately three times faster than the substitution rate of the control region, as shown by comparisons among six Ambystoma macrodactylum sequences and eight members of the Ambystoma tigrinum complex. We also found additional inserts within the intergenic spacers of five species that varied from 87-444 bp in length. The presence of the intergenic spacer in all sexual species of Ambystomatidae suggests that it arose at least 20 MYA and has been a stable component of the ambystomatid mtDNA ever since. As such, it represents one of the few examples of a large and persistent intergenic spacer in the mtDNA of any vertebrate clade.
我们报告了在蝾螈科所有有性物种的线粒体DNA（mtDNA）中，tRNAThr和tRNAPro之间存在一个共享的240碱基对基因间隔区。我们通过展示虎纹钝口螈（Ambystoma tigrinum tigrinum）1746碱基对的mtDNA序列来阐述该基因间隔区的背景信息，描述了钝口螈科所有物种中该基因间隔区的核苷酸组成，并将其与钝口螈及其他几种脊椎动物mtDNA的其他编码区和非编码区进行比较。通过对六个太平洋钝口螈（Ambystoma macrodactylum）序列和虎纹钝口螈复合体的八个成员进行比较发现，该基因间隔区的核苷酸替换率大约是控制区替换率的三倍。我们还在五个物种的基因间隔区内发现了额外的插入片段，其长度在87至444碱基对之间变化。钝口螈科所有有性物种中都存在该基因间隔区，这表明它至少在2000万年前就已出现，并且自此一直是钝口螈mtDNA的一个稳定组成部分。因此，它代表了任何脊椎动物类群mtDNA中大型且持久的基因间隔区的少数例子之一。
