大黄鱼16SrRNA和18SrRNA基因的测定与序列分析

利用多对引物，扩增并测定出大黄鱼16SrRNA基因和18SrRNA基因的部分序列，其长度分别为1202bp和1275bp，16SrRNA基因序列的GC含量为46．12％，18SrRNA基因的Gc含量为53．oo％。将大黄鱼16SrRNA基因序列与GenBank中15种硬骨鱼类的同源序列结合，同时将其18SrRNA基因序列与GenBank中9种脊索动物的同源序列相结合，运用软件获得各自序列间差异百分比，转换和颠换数值等信息。基于这两种基因序列，利用NJ法和BI法，分别构建16种硬骨鱼类和10种脊索动物的分子系统树。18SrRNA构建的系统树包括三大支，一支为哺乳类、鸟类和爬行类共6个物种，一支为两栖类的1个物种，另一支为2种硬骨鱼类。16SrRNA构建的系统树显示大黄鱼所在的石首鱼科与鲈科和盖刺鱼科亲缘关系较近。此外还讨论了这两个基因的序列特征。

Cloning and Sequence Analysis of 16S rRNA and 18S rRNA Genes Fragments of Larimichthys crocea

The partial nucleotide sequences of 16S rRNA gene and 18S rRNA gene were amplified and determined for Larimichthys crocea by PCR with several pairs of specific primers. The nt sequences of 16S and 18S rRNA genes of L. crocea were 1 202 bp and 1 275 bp in length, respectively. The G ＋ C content of 16S rRNA gene was 46.12 % , and the G ＋ C content of 18S rRNA gene was 53.00 %. The newly determined sequence of 16S rRNA gene ofL. crocea was analyzed together with homologous sequences of 15 fish species available in the GenBank database, and the determined sequence for 18S rRNA gene was combined with homologous sequences of 9 Chordate Species downloaded from Gen- Bank. The percentage nucleotide sequence divergence, and base substitutions were analyzed with the software. Based on 18S rRNA genes sequences, molecular phylogenetic trees constructed by neighbor-joining（ N J） and Bayesian （BI） methods supported the same topology, in which 9 species of vertebrates could be divided into three major monophyletic groups. The first group contained 6 species of amniotes. The second group comprised 1 species, Bufo guttatus, the member of Amphibians （ class Amphibia）. The remaining 2 species of fish belonged to the third group, with a clade comprising L. crocea, and Scophthalmus maximus. Another phylogenetic tree for 16 sequences of fish were derived using 16S rRNA gene and the same analytical approaches： NJ and BI, and Diplophos taenia（ AB034825 ） and Sigmops gracilis （AB016274） were used the outgroup species. The present results indicated that Sciaenidae was more closely related to Pomacanthidae and Percidae within Perciformes. In addition, several characteristics of 16S and 18S rRNA genes sequences were discussed in vertebrates.