Abstract: To construct and express a single chain variable(ScFv) fragment against ricin, VH and VL genes of anti-murine RT monoclonal antibody were cloned by RT-PCR from hybridoma cell secreting anti-RT McAb. ScFv gene was spliced by sequence overlap extending (SOE) PCR. ScFv gene was cloned into pMAL-p2X expression vector and transformed into TB1 E.coli. After positive clones were induced by IPTG for 18 hours，the identification of recombinant protein was detected by Western blotting. ScFv gene of VL-(Gly4Ser)3-VH was constructed successfully. The VH chain consisted of 363 bp and encoded 121 amino acids. The VL chain consisted of 324 bp and encoded 108 amino acids. SDS-PAGE and Western blotting analysis showed that the RT-ScFv gene was expressed in TB1 E.coli. The ScFv antibody expressed by pMAL-p2X fused with MBP tag protein and the relative molecular mass of fusion protein was about 75 ku. The expression vector of pMAL-RT-ScFv fusion protein was constructed successfully，and procured high performance expression.

Key words: 4D12; ScFv; protein expression; ricin