Garey J R, Wolstenholme D R
Department of Biology, University of Utah, Salt Lake City 84112.
J Mol Evol. 1989 May;28(5):374-87. doi: 10.1007/BF02603072.
The nucleotide sequence of a segment of the mitochondrial DNA (mtDNA) molecule of the liver fluke Fasciola hepatica (phylum Platyhelminthes, class Trematoda) has been determined, within which have been identified the genes for tRNA(ala), tRNA(asp), respiratory chain NADH dehydrogenase subunit I (ND1), tRNA(asn), tRNA(pro), tRNA(ile), tRNA(lys), ND3, tRNA(serAGN), tRNA(trp), and cytochrome c oxidase subunit I (COI). The 11 genes are arranged in the order given and are all transcribed from the same strand of the molecule. The overall order of the F. hepatica mitochondrial genes differs from what is found in other metazoan mtDNAs. All of the sequenced tRNA genes except the one for tRNA(serAGN) can be folded into a secondary structure with four arms resembling most other metazoan mitochondrial tRNAs, rather than the tRNAs that contain a T psi C arm replacement loop, found in nematode mtDNAs. The F. hepatica mitochondrial tRNA(serAGN) gene contains a dihydrouridine arm replacement loop, as is the case in all other metazoan mtDNAs examined to date. AGA and AGG are found in the F. hepatica mitochondrial protein genes and both codons appear to specify serine. These findings concerning F. hepatica mtDNA indicate that both a dihydrouridine arm replacement loop-containing tRNA(serAGN) gene and the use of AGA and AGG codons to specify serine must first have occurred very early in, or before, the evolution of metazoa.
已经确定了肝片吸虫（扁形动物门，吸虫纲）线粒体DNA（mtDNA）分子一段的核苷酸序列，其中已鉴定出tRNA（ala）、tRNA（asp）、呼吸链NADH脱氢酶亚基I（ND1）、tRNA（asn）、tRNA（pro）、tRNA（ile）、tRNA（lys）、ND3、tRNA（serAGN）、tRNA（trp）和细胞色素c氧化酶亚基I（COI）的基因。这11个基因按给定顺序排列，且都从分子的同一条链转录而来。肝片吸虫线粒体基因的总体顺序与其他后生动物mtDNA中的不同。除tRNA（serAGN）基因外，所有已测序的tRNA基因都能折叠成具有四个臂的二级结构，这与大多数其他后生动物线粒体tRNA相似，而不像线虫mtDNA中含有TψC臂替代环的tRNA。肝片吸虫线粒体tRNA（serAGN）基因含有一个二氢尿苷臂替代环，迄今为止在所有其他已检测的后生动物mtDNA中都是如此。在肝片吸虫线粒体蛋白质基因中发现了AGA和AGG，这两个密码子似乎都指定丝氨酸。这些关于肝片吸虫mtDNA的发现表明，含有二氢尿苷臂替代环的tRNA（serAGN）基因以及使用AGA和AGG密码子指定丝氨酸的现象肯定在后生动物进化的早期或之前就已出现。
