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基于对螺旋区随机堆积的ＲＮＡ二级结构的预测和密码子偏性计算，建立了ｐＢＶ２２０载体中外源基因高效表达的判别模型。该模型认为，外源基因的表达水平，与其５′端３０３９区域，以及３′端３０３９区域的二级结构自由能具有显著的统计学意义；其次与３′端９ｂｐ的局部密码子偏性相关。据此模型，我们设计了用于克隆表达ｒｉｃｉｎＡ链的引物。将ＰＣＲ扩增的基因克隆入ｐＢＶ２２０载体中，在ＤＨ５α宿主中获得了高效表达（表达水平在２０％以上），而且在ｐＥｘＳｅｃＩ载体系统中亦获得了高效表达。
Based on the prediction of RNA secondary structure randomly deposited in the helical region and codon bias calculation, a discriminant model of high expression of foreign genes in pBV220 vector was established. The model suggests that the expression level of exogenous gene has significant statistical significance with the free energy of the secondary structure at the 3’-3039 region and the 3’-terminal 3039 region, followed by the 3’-end 9 bp partial codon bias Sex related. Based on this model, we designed primers for the cloning of the ricin-A chain. The PCR amplified gene was cloned into pBV220 vector, which was highly expressed in DH5α host (the expression level was over 20%), and was also highly expressed in pExSecI vector system.