小黄鱼(Larimichthys polyactis)线粒体基因组结构与特征

COMPLETE SEQUENCE AND GENE ORGANIZATION OF MITOCHONDRIAL DNA OF THE SMALL YELLOW CROAKER LARIMICHTHYS POLYACTIS

采用长片段扩增策略,获得鲈形目石首鱼科黄鱼属小黄鱼的线粒体基因组全序列。组装分析结果表明,其长度为16470bp,H链碱基组成呈明显反G偏倚,G含量仅为16%。13个蛋白质基因起始密码子均为ATG。COI基因的终止密码子为AGA,ND1和ND3基因为TAG,COII、ND4和Cytb基因为不完全终止密码子T,其余7个基因都是完整的TAA。在小黄鱼mtDNA中发现2个特殊发夹结构,一个是轻链复制起始区(OL)的发夹环,位于tRNA簇,环区T含量仅为9%,而G含量达45%,这与哺乳动物和爪蟾该区域富含T有所不同。另一个假定发夹结构位于ATP6基因末端,这种二级结构可能与准确转录有关。该mtDNA控制区长度为799bp,5′端含有9个连续TA串联重复和2个5′-ATGTA---TACAT-3′重复,与已报道的鱼类扩展终止相关序列模式恰恰相反;中央控制区仅识别出CSB-E结构;保守序列区含有CSB-1,2,3,其中CSB-2具有高度保守性。对小黄鱼和大黄鱼的mtDNA比较进化研究,根据分子钟假说,估计二者线粒体基因组的进化分歧时间为4.8百万年前。

Based on the conserved region in mitochondrial DNA of Perciformes, the primers were designed to determine the complete mtDNA sequence of small yellow croaker Larimichthys polyactis by long PCR technique. As sequenced, the length was 16470bp, containing 13 protein-coding genes, two rRNA genes, 22 tRNA genes and non-coding regions. The total base composition of H strand was characterized by the negative bias for G （16%）. All protein-coding genes of L. polyactis mtDNA used ATG as the initiation codons. Seven proteincoding genes terminated with TAA. COI gene ended with TGA; ND1 and ND3 genes ended with TAG; and COII, ND4, Cyt b genes ended with incomplete stop codon, i.e. a single stop nucleotide T. Two putative hairpin structures were detected in this species. One was in the origin of the light strand replication （OL）, which was located in a cluster of five tRNA genes （tRNA-Trp, Ala, Asn, Cys and Tyr）. The other hairpin structure was identified in the end of ATP6 gene, This secondary structure might be related to the mtDNA transcription. The control region of L. polyactis was located between tRNAPro and tRNAPhe, with 799bp in length. Nine copies of TA tandem repeats and two repeats ＂-ATGTA---TACAT-＂ were found in 5′-end of control region. Only CSB-E was detected in central conserved domain. Three conserved sequence blocks CSB-1, CSB-2 and CSB-3 were found at the 3′-end of the control region. CSB-2 was the most conservative in fishes. Compared with the mtDNA of large yellow croaker L. crocea, the DNA sequence similarity of 12S and 16S rRNA genes was the highest （96%）, while the amino acid sequence similarity of ND6 gene was the lowest （83%）. According to the molecular clock, the divergence between small and large yellow croaker happened 4.8 million years ago by compared with their mtDNA sequences.