猪瘟病毒属于黄病毒科瘟病毒属，对我国养猪业造成严重威胁。该病毒编码的非结构蛋白NS5B是一种依赖RNA的RNA聚合酶，在病毒RNA基因组复制过程中发挥核心作用。与黄病毒科的丙型肝炎病毒和乙型脑炎病毒的聚合酶相比，猪瘟病毒NS5B拥有一段独特的、约90个氨基酸的N端结构域（NTD）。已有研究表明该NTD可调节聚合酶功能，但具体机制不明；而已报道的瘟病毒NS5B的晶体结构中亦缺乏NTD的结构信息。我们近期在NS5B相关研究中发现了NTD调控聚合酶功能的关键证据，将在本项目中进一步利用蛋白质晶体学方法获取NTD自身及其与聚合酶相互作用的三维结构信息，利用体外生物化学方法研究NTD对聚合酶催化过程的调控机制，并在此基础上利用重组病毒对NTD的生物学功能进行体内验证。同时，我们还将基于NTD的结构与功能信息寻找干预NS5B聚合酶功能的新策略，为针对NS5B的抗病毒研究提供科学依据。

The classical swine fever virus (CSFV) belongs to the Pestivirus genus in the Flaviviridae family, and is a serious threat to the pig industry in China. NS5B, a nonstructural protein encoded by CSFV, possesses RNA-dependent RNA polymerase function and plays essential roles in viral RNA genome replication. Compared to other Flaviviridae polymerases such as those from hepatitis C virus and Japanese encephalitis virus, the CSFV NS5B includes a unique 90-residue N-terminal domain (NTD). Biochemical studies have suggested that NTD regulates the polymerase function in NS5B, but the mechanistic details remain elusive. In addition, structural information of NTD is lacking in available pestivirus NS5B crystal structures. Recently, we have obtained key evidences toward the understanding of the regulatory roles of NS5B NTD, and will proceed to unravel the mechanisms in this project. We will obtain the structural information of NTD itself and its interaction with the core polymerase region by protein crystallography. We will also investigate how NTD regulates polymerase function through in vitro biochemical approaches, and will then validate the biological function of NTD in vivo using recombinant viruses. Moreover, we will try to find intervention strategies against NS5B based on the structure and function of NTD, and to provide a scientific basis for antiviral studies targeting CSFV NS5B.