A total of 76 different nucleotide acid sequences of MHC gene, which were classed as 20 alleles, were identified in 185 clones from 16 resistant and 21 susceptible "whole red" color patterns of Cyprinus carpio var. Color individuals using the specific primer pair of DABF and DABR. The 624 bp-long nucleotide fragment consisted of the exonl,exon2,exon3 and exon4,encoding signal peptide,Bl domain, B2 domain and part transmembrane,respectively. There were 144 nucleotide(52. 17% )and 70 amino acid(76.07% ) variable sites in the 276 bp-long pi domain, whereas the nucleotide and amino acid variable sites were 98 (34. 75% )and 50(53. 19% ) in the 282 bp-long B2 domain. It was obviously found that Bl domain had more variable sites than B2 domain. Mean while, 23 variable sites were observed in total 24 peptide binding residues(PBR)of β1 domain. The ω values(<ω = dN/ds) were 1. 367,0. 886,and 0. 754 for PBR and non-PBR of the Bl domain,and for B2 domain,respectively,implying positive selection pressure conducted on the MHC-DAB gene (especially for Bl domain) of C. Carpio var. Color. The percentage (13. 75% )of Cyca-DAB3 * 15 was significantly higher in the resistant stock than that (3. 81% ) in the susceptible stock (P < 0.05). Interestingly,the Cyca-DAB3 *09 and Cyca-DAB3 * 10 were only found in the resistant stock,with percentage of 3. 75% (P <0.05), whereas the Cyca-DAB3 * 02 and Cyca-DAB3 * 14 were only observed in the susceptible stock, with the percentage of 7. 62% (P <0. 05) and 8. 57% (P < 0. 01), respectively. The present results would be useful to conduct the disease-resistant breeding program in the C. Carpio var. Color.%利用一对特异性引物DABF和DABR,分别从21尾感病和16尾抗病“全红”体色瓯江彩鲤的cDNA中,扩增出长度为624 bp的MHC-DAB基因片段.共测序185个有效克隆,获得76个不同的核苷酸序列.MHC-DAB基因片段包括第1～4外显子,分别编码信号肽、β1和β2结构域及跨膜区.长度为276 bp的β1结构域有144个核苷酸变异位点(52.17％)和70个氨基酸变异位点(76.07％),而长度为282 bp的β2结构域只有98个核苷酸变异位点(34.75％)和50个氨基酸变异位点(53.19％),显示β1结构域的变异要明显大于β2结构域.在β1结构域的24个抗原结合位点(PBR)上,有23个发生了变异.β1结构域的PBR、非抗原结合位点( non-PBR)及β2结构域的ω值(ω=dN/ds)分别为1.367、0.886和0.754,表明“全红”体色瓯江彩鲤MHC-DAB基因(特别是β1结构域)在进化过程中受到正向选择作用.在所得的20个不同的等位基因中,基因DAB3*15在抗病群体中出现的频率(13.75％)显著高于感病群体中出现的频率(3.81％)(P＜0.05)；基因DAB3*09和DAB3*10的出现频率都为3.75％(P＜0.05),仅存在于抗病群体中；而基因DAB3*02和DAB3*14的出现频率分别为7.62％ (P ＜0.05)和8.57％(P＜0.01),仅存在于感病群体中.
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