The non-structural protein 1 (NS1) of influenza A virus (IAV) is a key player in inhibiting antiviral response in host cells, thereby facilitating its replication. However, other roles of NS1, which are independent of antagonising host cells’ antiviral response, are less characterised. To investigate these unidentified roles, we used a recombinant virus, which lacks NS1 expression, and observed its phenotypes during the infection of antiviral defective cells (RIG-I KO cells) in the presence or absence of exogeneous NS1. Moreover, we used virus-like particle (VLP) production system to further support our findings. Our experiments demonstrated that IAV deficient in NS1 replicates less efficiently than wild-type IAV in RIG-I KO cells and this replication defect was complemented by ectopic expression of NS1. As suggested previously, NS1 is incorporated in the virion and participates in the regulation of viral transcription and translation. Using the VLP production system, in which minigenome transcription or viral protein production was unaffected by NS1, we demonstrated that NS1 facilitates viral genome packaging into VLP, leading to efficient minigenome transfer by VLP. Furthermore, the incorporation of NS1 and the minigenome into VLP were impaired by introducing a point mutation (R38A) in the double stranded RNA-binding domain of NS1. These results suggest a novel function of NS1 in improving genome packaging in a dsRNA binding-dependent manner. Taken together, NS1 acts as an essential pro-viral regulator, not only by antagonizing host immunity but also by facilitating viral replication and genome packaging.

中文翻译：

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甲型流感病毒NS1通过以dsRNA结合依赖性方式增强基因组包装来优化病毒感染性。

甲型流感病毒（IAV）的非结构蛋白1（NS1）是抑制宿主细胞中抗病毒反应从而促进其复制的关键因素。然而，NS1的其他角色，与拮抗宿主细胞的抗病毒反应无关，其特征较少。为了研究这些未知的作用，我们使用了一种缺乏NS1表达的重组病毒，并在存在或不存在外源NS1的情况下感染抗病毒缺陷细胞（RIG-I KO细胞）期间观察了其表型。此外，我们使用病毒样颗粒（VLP）生产系统进一步支持了我们的发现。我们的实验表明，在RIG-I KO细胞中，缺乏NS1的IAV的复制效率不如野生型IAV，并且这种复制缺陷得到了NS1异位表达的补充。如前所述，NS1整合在病毒体中，并参与病毒转录和翻译的调控。使用VLP生产系统，其中微型基因组转录或病毒蛋白的生产不受NS1的影响，我们证明了NS1促进了病毒基因组包装到VLP中，从而导致VLP有效地转移了微型基因组。此外，通过在NS1的双链RNA结合结构域中引入点突变（R38A），削弱了NS1和微型基因组进入VLP的能力。这些结果表明NS1以dsRNA结合依赖性方式改善基因组包装的新功能。两者合计，NS1不仅通过拮抗宿主免疫力，而且还通过促进病毒复制和基因组包装，充当着重要的前病毒调节剂。