And two enzyme sites bamh i and xba i were introduced at 5 " terminal and 3 " terminal of the amplified fragment . the result of rt - pcr showed that the designed fragment was amplified with expected molecular weight and sequenced by automatic sequencing Rt - pcr结果表明,扩增出符合预期分子量大小的dna片段,经测序确定为fmdv3a 。序列分析后选取2株差异毒株进行大肠杆菌原核表达。