Pont-Kingdon G, Vassort C G, Warrior R, Okimoto R, Beagley C T, Wolstenholme D R
Department of Biology, University of Utah, Salt Lake City, UT 84112, USA.
J Mol Evol. 2000 Oct;51(4):404-15. doi: 10.1007/s002390010103.
The 3231-nucleotide-pair (ntp) sequence of one end of one of the two linear mitochondrial (mt) DNA molecules of Hydra attenuata (phylum Cnidaria, class Hydrozoa, order Anthomedusae) has been determined. This segment contains complete genes for tRNA(f-Met), l-rRNA, tRNA(Trp), subunit 2 of cytochrome c oxidase (COII), subunit 8 of ATP synthetase (ATPase8), and the 5' 136 ntp of ATPase6. These genes are arranged in the order given and are transcribed from the same strand of the molecule. As in two other cnidarians, the hexacorallian anthozoan Metridium senile and the octocorallian anthozoan Sarcophyton glaucum, the mt-genetic code of H. attenuata is near standard. The only modification appears to be that TGA specifies tryptophan rather than termination. Also as in M. senile and S. glaucum, the encoded H. attenuata mt-tRNA(f-Met) has primary and secondary structural features resembling those of Escherichia coli initiator tRNA(t-Met). As the encoded mt-tRNA(Trp) cannot be folded into a totally orthodox secondary structure, two alternative forms are suggested. The encoded H. attenuata mt-l-rRNA is 1738 nt, which is 451 nt shorter than the M. senile mt-l-rRNA. Comparisons of secondary structure models of these two mt-l-rRNAs indicate that most of the size difference results from loss of nucleotides in the H. attenuata molecule at a minimum of 46 locations, which includes elimination of six distinct helical elements.
已确定了细螅（刺胞动物门、水螅纲、花水母目）两个线性线粒体（mt）DNA分子之一一端的3231个核苷酸对（ntp）序列。该片段包含tRNA（f-Met）、l-rRNA、tRNA（Trp）、细胞色素c氧化酶亚基2（COII）、ATP合酶亚基8（ATPase8）以及ATPase6的5'端136个ntp的完整基因。这些基因按给定顺序排列，并从分子的同一条链转录。与另外两种刺胞动物，即六放珊瑚亚纲的海葵和八放珊瑚亚纲的海鳃一样，细螅的线粒体遗传密码接近标准密码。唯一的修改似乎是TGA编码色氨酸而非终止密码子。同样与海葵和海鳃一样，细螅编码的线粒体tRNA（f-Met）具有与大肠杆菌起始tRNA（t-Met）相似的一级和二级结构特征。由于编码的线粒体tRNA（Trp）无法折叠成完全正统的二级结构，因此提出了两种替代形式。细螅编码的线粒体l-rRNA为1738个nt，比海葵的线粒体l-rRNA短451个nt。对这两种线粒体l-rRNA二级结构模型的比较表明，大部分大小差异是由于细螅分子中至少46个位置的核苷酸缺失造成的，其中包括六个不同螺旋元件的缺失。
