不同H9N2亚型鸭流感病毒NS1基因克隆和功能进化分析

禽流感病毒（AIV）在高免疫压力情况下会发生变异而逃避免疫系统的监视。其NS1蛋白共有230个氨基酸，其中前73个氨基酸残基以二聚体形式存在，包含了所有RNA的结合活性。NS1的氨基端1—73位是mRNA的结合区，氨基端1—100位是双股RNA依赖性蛋白激酶（PKR）的结合区。PKR抗病毒作用机制如下：病毒侵染宿主细胞时，在宿主干扰素的诱导下，双股RNA与PKR结合，同时真核翻译启动子α亚单位发生磷酸化，导致PKR的激活。激活的PKR能同时抑制宿主细胞和病毒mRNA的翻译，从而最终抑制入侵病毒在细胞中的有效繁殖和扩散。

Cloning and Phylogenetic Analysis of NS1 Genes from Different Isolates of H9N2 Subtype Duck Influenza Virus

Objective] The study aimed to lay a foundation for the further studies on function mechanism of NS1 protein in the interspecies transmission of waterfowl influenza virus. Method] Using the serologic assay and the specific RT-PCR method, some strains of H9 subtype waterfowl influenza virus were isolated from the 12 to 20 day-old muscovy duck flocks without any clinical symptoms in different areas of Guangdong Province. Four of these strains, including A/duck/ZQ/303/2007(H9N2) (A3 for short), A/Duck/FJ/301/2007(H9N2) (C1 for short), A/Duck/NH/306/2007(H9N2) (D6 for short), A/duck/SS/402/2007(H9N2) (E2 for short), and a strain named A/duck/ZC/2007(H9N2) (L1 for short) from a muscovy duck died of avian influenza virus (AIV), were used for NS1 gene cloning and sequencing. Subsequently, the obtained NS1 gene sequences were compared with other NS1 sequences registered in GenBank, and the phylogenetic analysis was also conducted. Result] When compared with the H9N2 AIV NS1 sequences in GenBank, the NS1 genes of the four AIV strains A3, C1, D6 and E2 displayed homologies ranging from 99% to 100% at nucleotide level, and 95% to 100% at amino acid level; while the NS1 gene of L1 strain displayed homology ranging from 94% to 97% at nucleotide level, and 93% to 98% at amino acid level. The phylogenetic tree demonstrated that A3, C1, D6 and E2 were highly resemblant, and L1 was closest to AY66473 (chicken, 2003). By comparison with the NS1 gene sequences of L1, AF523514 (duck), AY664743 (chicken) and EF155262.1 (quail) using DNAstar, A3, C1, D6 and E2 presented nucleotide variations at site 21(R→Q), 70, 71(KE→EG), 86 (A→S), 124 (V→M) and 225 (S→N), and amino acid variations at site 21, 70, 71 and 86 in dsRNA-dependent protein kinase (PKR) binding domain of NS1 gene, which induced the evident variations of antigenic determinant and surface probability plot of NS1 protein. Conclusion] This study suggested that the amino acid sequence variation in PKR binding domain of NS1 protein had something to do with the virus pathogenicity.