Lu Y, Wambach M, Katze M G, Krug R M
Department of Molecular Biology and Biochemistry, Rutgers, State University of New Jersey, Piscataway 08855, USA.
Virology. 1995 Dec 1;214(1):222-8. doi: 10.1006/viro.1995.9937.
The NS1 protein of influenza A virus binds not only to poly(A) and a stem-bulge region in U6 small nuclear RNA (snRNA), but also to double-stranded (ds) RNA. Binding assays with NS1 protein mutants established that the previously identified RNA-binding domain of the NS1 protein is required for binding to ds RNA as well as for binding to poly(A) and U6 snRNA. In addition, dsRNA competed with U6 snRNA for binding to the NS1 protein, consistent with both RNAs sharing the same binding site on the protein. As a consequence of its binding to dsRNA, the NS1 protein blocks the activation of the dsRNA-activated protein kinase (PKR) in vitro. This kinase phosphorylates the alpha subunit of eukaryotic translation initiation factor 2 (elF-2 alpha), leading to a decrease in the rate of initiation of translation. Assays using purified PKR and purified elF2 demonstrated that the NS1 protein blocks the dsRNA activation of PKR, and experiments using reticulocyte extracts showed that the NS1 protein blocks the inhibition of translation caused by dsRNA activation of PKR. The implications of these results for control mechanisms occurring in influenza virus-infected cells are discussed.
甲型流感病毒的NS1蛋白不仅能与多聚腺苷酸（poly(A)）以及U6小核RNA（snRNA）中的一个茎环结构区域结合，还能与双链（ds）RNA结合。对NS1蛋白突变体进行的结合试验表明，先前确定的NS1蛋白的RNA结合结构域对于与dsRNA结合以及与poly(A)和U6 snRNA结合都是必需的。此外，dsRNA与U6 snRNA竞争与NS1蛋白的结合，这与两种RNA在该蛋白上共享相同的结合位点一致。由于其与dsRNA的结合，NS1蛋白在体外可阻断dsRNA激活蛋白激酶（PKR）的激活。该激酶使真核翻译起始因子2（elF-2α）的α亚基磷酸化，导致翻译起始速率降低。使用纯化的PKR和纯化的elF2进行的试验表明，NS1蛋白可阻断PKR的dsRNA激活，而使用网织红细胞提取物进行的实验表明，NS1蛋白可阻断由PKR的dsRNA激活所导致的翻译抑制。文中讨论了这些结果对流感病毒感染细胞中发生的调控机制的影响。
