Delarbre C, Barriel V, Tillier S, Janvier P, Gachelin G
Unité de Biologie Moléculaire du Gène, Institut National de la Santé et de la Recherche Médicale, Institut Pasteur, Paris, France.
Mol Biol Evol. 1997 Aug;14(8):807-13. doi: 10.1093/oxfordjournals.molbev.a025821.
We have cloned the mitochondrial DNA fragment extending from tRNA-Leu to the cytochrome oxidase subunit 1 (COI) genes of Branchiostoma lanceolatum, Myxine glutinosa, Lampetra fluviatilis, and Scyliorhinus caniculus and have determined their respective gene sequences and organization. In all four species, this region contains the ND1 and ND2 genes and the genes coding eight tRNAs, namely, tRNA-Ile, -Gln, -Met, -Trp, -Ala, -Asn, -Cys, and -Tyr. The gene order is the same in the hagfish, lamprey and dogfish. In the lancelet, the location of the tRNA genes is slightly different. The mitochondrial code of Myxine, Lampetra, and Scyliorhinus is identical to that of vertebrates. The code used by the lancelet is the same with the exception of AGA (a stop codon in vertebrates), which codes for glycine in the lancelet. From the comparison of the four maps with already published ones for other species, we propose that the main features of the craniate mtDNA between the ND1 and COI genes were established in the common ancestor to cephalochordates and vertebrates more than 400 MYA. The origin of replication of the light-strand (Ori-L), usually located between the tRNA-Asn and tRNA-Cys genes in vertebrates, was not found in the lancelet, hagfish, or lamprey (Lampetra). In contrast, it was found in the dogfish. Thus the position of Ori-L was established for the first time in the common ancestor to the Chondrichthyes and Osteichthyes and remained present in all later-emerging vertebrates.
我们克隆了文昌鱼、盲鳗、七鳃鳗和小斑猫鲨从tRNA-亮氨酸到细胞色素氧化酶亚基1（COI）基因的线粒体DNA片段，并确定了它们各自的基因序列和组织结构。在所有这四个物种中，该区域包含ND1和ND2基因以及编码8种tRNA的基因，即tRNA-异亮氨酸、-谷氨酰胺、-甲硫氨酸、-色氨酸、-丙氨酸、-天冬酰胺、-半胱氨酸和-酪氨酸。盲鳗、七鳃鳗和鲨鱼的基因顺序相同。在文昌鱼中，tRNA基因的位置略有不同。盲鳗、七鳃鳗和小斑猫鲨的线粒体密码与脊椎动物的相同。文昌鱼使用的密码与脊椎动物相同，只是AGA（在脊椎动物中为终止密码子）在文昌鱼中编码甘氨酸。通过将这四个图谱与已发表的其他物种的图谱进行比较，我们提出，在头索动物和脊椎动物的共同祖先中，早在4亿多年前就确立了ND1和COI基因之间有头类线粒体DNA的主要特征。轻链复制起点（Ori-L）通常位于脊椎动物的tRNA-天冬酰胺和tRNA-半胱氨酸基因之间，在文昌鱼、盲鳗或七鳃鳗中未发现。相反，在鲨鱼中发现了它。因此，Ori-L的位置首次在软骨鱼纲和硬骨鱼纲的共同祖先中确立，并在所有后来出现的脊椎动物中保留下来。
