病毒与宿主在相互博弈过程中，病毒毒力过强或宿主过度免疫反应均不利于两者自身生存。两者共生的调控机制多种多样。前期研究表明H5N1禽流感病毒因其NS1蛋白效应区自然缺失EALQR基序而致毒力减弱，可以和宿主共生，但系统性的致病机制研究不足。针对该基序影响病毒致病表型的现象，拟从其调控病毒复制、基因转录翻译以及免疫信号通路等病毒与宿主相互作用层面入手，利用生化实验和结构生物学等技术手段，通过确定该基序影响NS1二聚体结构和TRIM25寡聚化，进而减弱RNA结合能力及TRIM25介导的RIG-I泛素化，同时利用拯救的重组病毒感染关键基因敲除的细胞或小鼠，在病毒水平和生理状态下验证该基序的生物学效应，初步阐明该基序调控病毒复制和宿主免疫应答的分子基础。本研究成果将揭示病毒为了生存而降低对宿主的致病力，从而达到和宿主共生的调控机制，同时为研发流感减毒疫苗以及小分子药物奠定理论基础。

Too strong virulence or abundant immune responses are harmful to the both sides during the battle between the virus and the host immune system. It has been reported that there are a number of various ways to reach a commensal status. Our previous study indicated that an H5N1 avian influenza virus isolated from swine in the field with a naturally-deleted EALQR motif in its non-structural protein 1 (NS1) effector domain is attenuated to SPF chickens and could replicate well in the chickens without any clinical symptoms.However, the scientific question is that the pathogenesis in animals or cells is not fully investigated yet. Our current project aims to reveal a new mechanism by how the naturally-deleted NS1 without EALQR motif affects virus replication, host gene transcription and translation and innate signaling pathway, resulting in the virulent attenuation. Using the techniques of biochemistry or structure biology, etc, we would anticipate elucidating the naturally-deleted NS1 weakens the TRIM25-mediated RIG-I ubiquitination and RIG-I recognizing and binding to double-stranded RNA by destorying TRIM25 oligomerization and NS1 dimerization, further impairing the inhibition of activation of RIG-I signaling pathway and IFN production. Meanwhile, based on the reverse genetic system of influenza virus and the CRISPR-Cas9 technology, we will confirm the functions of EALQR motif at the live influenza virus level and physiological condition by infecting key gene-knockout (such as RIG-I-/-, TRIM25-/-) cells or mice with different rescued viruses. Our expected data will uncover the molecular basis of virus-host commensalism via decreasing the blockade of host antiviral responses, and provide the support for the development of attenuated vaccines and small molecular drugs against influenza viruses.