中文摘要：

猪瘟病毒（CSFV）疫苗株Thiverval株与亲本病毒Alfort株相比，最明显的区别就是其3′-UTR含有一定长度的插入序列。本研究通过反向遗传学操作，构建了3′-UTR含有19nt、32nt以及插入片段完全缺失的CSFVThiverval株全长cDNA感染性克隆，将突变病毒基因组进行体外转录，利用BHK-21细胞转染、PK-15细胞传代增殖的方式成功的从3种重组突变感染性克隆中拯救出活病毒粒子，表明CSFV疫苗株3′-UTR插入片段并不影响病毒的拯救。通过3′-UTR二级结构模拟，发现疫苗株的插入片段导致3′-UTR空间构型发生改变、自由能升高、影响二级结构的稳定性，可能是导致疫苗株毒力减弱的原因之一。

英文摘要：

The Thiverval vaccine strain of classical swine feuer virus （CSFV） differs from its parent Alfort strain by having an insertion in the 3′-UTR of genome. In this study, a series of CSFV Thiverval strain infectious cDNA clone with different insertions or complete deletion of insertion in the 3′-UTR were constructed through reverse genetics. Viruses were rescued from all the cDNA clone using the BHK-21 cells for transfection and PK-15 cells for multiplication. The results showed that insertion in 3′-UTR of attenuated CSFV did not effect the virus rescue, and it was not the decisive factor for maintaining viable virus. Secondary structure Modeling of the 3′-UTR suggests that the T-rich insertion could result in the change of structure and free energy, thus affecting the stability of the 3′-UTR structure, which could account for the attenuation of vaccine strain.