The pcDNA3.1mycHisA plasmids encoding CAT [17] , NSD6-30, NSD31-55, NSD56-80, NSD81-105, NSD106-130, NSD131-155, NSD156-180, NSD181-205, NSD206-230, NSD231-248, NSD249-265, NSs-E253-255A/D257-259A, NSs-E253-255A or NSsD257-259A were linearized, and in vitro transcribed by using mMESSAGE mMACHINE T7 Ultra kit (Ambion) according to manufacturer's instruction. The linearized CAT DNA contained myc-His tag at the 39end.