国产IBV疫苗株核衣壳蛋白基因的亲缘关系

利用自行设计的引物Cx和Cs，通过RT－PCR方法分别扩增出鸡传染性支气管炎病毒（IBV）D41株，H120GD株、H120SH株、H52GD株等4个国产疫苗株和标准强毒M41－E4株完整的N基因cDNA,然后将其分别克隆到pGEM T-Easy或pMD 18-T载体中并测序。测序结果表明，这5个IBV毒株可分2组，其中D41株，H120GD株和H120SH株为一组，它们的核苷酸和推导氨基酸序列同源性为99．7％－99．8％和99．0％－99．5％，而H52GD株与M41－E4株构成另一组，其核苷酸和推导氨基酸序列同源性为99．7％和99．5％；而2组之间的最大同源性仅为91．0％和93．2％。在系统发生进化树上，这2组分别位于不同的分支簇上。值得注意的是，国内的H52GD株与国外报道的H52株不在同一分支簇上，相反却与国内强毒M41－E4株以及国外报道的M41株在同一分支簇上。这一结果表明，国内的H52GD疫苗株与国外报道的H52疫苗株不同，它们在亲缘关系上更靠近M41－E4株和M41株。

Genetic Relationship of Nucleocapsid Gene of Domestic IBV Vaccine Strains

The nucleocapsid protein gene(N gene) of IBV strain D41,H120GD,H120SH,H52GD and M41-E4 were amplified by RT-PCR with a pair of specific oligonucleotide primers(Cx/Cs) and cloned into plasmid pGEM-T Easy and pMD 18-T respectively.The inserts were sequenced and the results revealed that the complete N genes of strains D41,H120GD,H120SH,H52GD and M41-E4 were all composed of 1 230 bp,coding for 409 amino acids respectively.Sequence analysis revealed that the five IBV strains could be divided into two groups,i.e.,strains D41,H120GD and H120SH formed one group and there was 99.7%-99.8% nucleotide sequence homology and 99.0%-99.5% deduced amino acid sequence homology between strains D41,H120GD and H120SH;while strains H52GD and M41-E4 constituted another group and they had 99.7% nucleotide sequence homology and 99.5% deduced amino acid sequence homology each other.But the highest homology between the two groups was only 91.0% and 93.2%.The two groups fell into two different branches of a phylogenetic tree.It was noteworthy that domestic vaccine strain H52GD was not in the same branch with foreign H52 strain,but with domestic virulent M41-E4 strain and foreign M41 strain.The study suggested domestic H52 strain(H52GD) was different from foreign H52 strain because the former was more genetically related to domestic virulent M41-E4 strain and foreign M41 strain.