[Objective] The aim was to clone the conserved sequences of cry gene and express them in Rosetta （DE3）. [Method] Specific primers were designed according to NCBI database information and the conserved sequences of cry gene were amplified by PCR from Bt transgenic cotton. Then recombinant plasmids were constructed and expressed in E. coil strain Rosetta （DE3）. Finally, the effects of different concentrations and inducing time of IPTG on the expression level of protein were investigated. [Result] Two conserved sequences （304 and 853 bp respectively） of cry gene were amplified. The result of SDS-PAGE confirmed that the recombinant plasmids pGEX-4t-I-304 and pGEX-4t-1-853 could express fusion proteins by IPTG induction and the molecular weight of protein products was 39 and 62.4 kDa respectively, which was in accordance with predicted result. The optimal protein ex- pression conditions were confirmed as induction with 0.15 mmol/L IPTG for 7 h. [Conclusion] This study prepared the ground for the further detection of Bt transgenic crops.
