PRRSV是迄今为止报道最容易变异的RNA病毒。RNA依赖性RNA聚合酶（RdRp）影响PRRSV遗传稳定性的关键功能域还不清楚。根据化学诱变筛选得到的Ribavirin抗性PRRSV毒株具有高保真性的现象，本项目拟研究PRRSV RdRp影响病毒遗传稳定性的关键功能域。首先构建Ribavirin抗性PRRSV感染性克隆和设计RdRp突变回补试验并拯救病毒；同时构建PRRSV感染性克隆和设计PRRSV RpRd突变体并拯救病毒，分别进行病毒遗传稳定性评价，确认RdRp影响PRRSV遗传稳定性的关键位点；然后分别表达和纯化PRRSV RdRp及突变体重组蛋白，进行蛋白结晶和结构解析，比较PRRSV RdRp及其突变体蛋白结构变化，确定RdRp影响PRRSV遗传稳定性的关键功能域。本结果不仅能揭示RdRp影响PRRSV遗传稳定性的作用机制，更可为研制高保真PRRSV弱毒疫苗提供理论基础。

PRRSV is the most easily mutated RNA virus reported so far. The key functional domains of RNA-dependent RNA polymerase (RdRp) affecting the genetic stability in PRRSV remain unclear. According to the fact that the high fidelity of ribavirin resistant PRRSV strains screened by chemical mutagenesis. The project aims to study the key functional domains of PRRSV RdRp affecting the virus genetic stability. Firstly, we constructed infectious clone of ribavirin resistant PRRSV and designed site-directed mutagenesis rescue experiment of RdRp to rescue the viruses. At the same time, we constructed infectious clone of PRRSV and designed PRRSV RpRd mutant and rescued the viruses. Thereafter, we evaluated the genetic stability of the viruses to confirm the key sites of RdRp affecting the genetic stability of PRRSV. Then RdRp and its mutant recombinant protein were expressed and purified respectively, and carried out protein crystallization. At last crystalline structure analysis was used to compare the structural changes of PRRSV RdRp and its mutants, and to determine the key functional domains of RdRp affecting the genetic stability of PRRSV. The results will reveal the mechanism of RdRp affecting the genetic stability of PRRSV, as well as provide theoretical basis for the design of genetically stable high-fidelity attenuated PRRSV vaccine.