白鱀豚MHC基因类DQB1座位第二外元的序列变异分析  

Sequence variation at exon 2 of the major histocompatibility complex DQB1-like locus in the Baiji (Lipotes vexillifer)

作　　者：严洁[1] 杨光[1] 周开亚[1] 魏辅文[2] 

机构地区：[1]南京师范大学生命科学学院遗传资源研究所,南京210097 [2]中国科学院动物研究所,北京100080

出　　处：《动物学报》2003年第4期501-507,共7页ACTA ZOOLOGICA SINICA

基　　金：国家自然科学基金 (No .3 0 2 70 2 12和No .3 0 0 70 116);国家杰出青年科学基金 (No.3 0 12 5 0 0 6);国家"2 11工程""十五"建设项目;江苏省"青蓝工程"中青年学术带头人科研基金资助~~

摘　　要：测定了 4 5个克隆的白豚 (Lipotesvexillifer)MHCⅡ类基因DQB座位第二外元 172bp的核苷酸序列 ,共获得 15种序列 ,发现了 2 2个变异位点。核苷酸的非同义替换明显多于同义替换 ,并造成了 15个氨基酸的改变。氨基酸的替换趋于集中在假定的与抗原的选择性识别相关的位点附近。白豚DQB基因的核苷酸和氨基酸序列与文献报道的白鲸 (Delphinapterusleucas)和一角鲸 (Monodonmonoceros)DQB1序列具有较高的同源性。氨基酸序列不具备人及其它一些灵长类动物DQB2基因所共有的基序 (Motif) ,而与牛DQB1基因的基序相近 ,说明本研究得到的白豚MHC序列应属于类DQB1基因。同一个体出现了多种序列的情况 ,提示白豚的DQB基因可能存在着座位重复。白豚的类DQB1座位的序列中存在多种基序的不同组合 ,推测是由于基因转换造成的.We investigated genetic variation at exon 2 (including part of the putative peptide-binding region, PBR) of the class Ⅱ major histocompatibility complex (MHC) DQB locus in the Baiji (Lipotes vexillifer). PCR products were cloned into a pMD-18T vector after purification. Almost 15 recombinant plasmids for each individual were screened out, isolated, purified, and then sequenced. Within the 172 bp nucleotide sequences of 45 clones from three individuals, 22 variable sites were determined and 15 sequences were attained. All 15 sequences did not show deletions, insertions, or stop codons, and therefore could be assumed functional in vivo. Phylogenetic trees reconstructed using the neighbor joining (NJ) method contained in the MEGA (Molecular Evolutionary Genetics Analysis) software package divided the 15 sequences into two monophyletic clades. Seven nucleotide acid and four amino acid diagnostic sites were found between these two clades. Within the four diagnostic amino acid sites, non-conservative amino acid substitution was found at site 28, suggesting that the variation at this site would be responsible for recognition and presentation of different kinds of peptides. The ratio of nonsynonymous substitutions was much higher than that of synonymous substitutions (d N/d S=6 59/2 57), which caused 15 amino acid differences. Substitutions of amino acid tended to be clustered around sites postulated to be responsible for selective peptide recognition. Nucleotide acid and amino acid sequences both showed high level of similarity (nucleotide acid: 90 7%; amino acid: 80 6%) to DQB1 alleles of the beluga whale (Delphinapterus leucas) and narwhal (Monodon monoceros). Amino acid sequences did not share motifs with human and some other primates, but showed similarity to that of BoLA-DQB1. Therefore, the present sequences were all identified as DQB1-like locus. More than two sequences were found in each individual, suggesting duplication in the locus examined. Different motif recombination among sequences were also foun

关 键 词：白鱀豚 MHC基因 DQB1座位 序列变异分析 基因重复 基因转换 

分 类 号：Q953[生物学—动物学]