Objective To make high efficiency expression of the SAG2 gene from Toxoplasma gondii RH strain in E.coli and study the antigenicity of the expressed product. Methods The SAG2 gene fragment of T.gondii RH strain amplified by PCR method from genome DNA was cloned into the pMD-18T vector and transformed into E.coli DH5α. After nucleotide sequencing, the SAG2 gene fragment was subcloned into the expression vector pET23a with correct orientation and transformed into E.coli DH5α. The plasmid from the correct clone identified by PCR method and endonuclease digestion was transformed into E.coli BL21(DE3) and induced for expression. The expressed product was studied by SDS PAGE and Western blot. Results 502 bp gene fragment was amplified by PCR as anticipated. Nucleotide sequencing showed a 100% homology with that of the published sequence in GenBank. The molecular weight of the expressed protein was about Mr 19000. Western blotting indicated that the antigenicity of the protein was specific. Conclusion The plasmid pET 23a SAG2 was constructed and a high efficiency expression of the SAG2 gene from T.gondii RH strain was made. The expressed product shows a specific antigenicity.
