Abstract: Objective To analyze the difference of GRA7 gene of Toxoplasma gondii different isolated strains and express GRA7 in Escherichia coli. Methods The GRA7 gene was amplified from genomes of T.gondii isolates by PCR and was cloned into pGEX-4T-1. The recombinant plasmid was transformed into JM109 and sent to be sequenced. The sequence was analyzed with CLUSTALW (an internet tool). The recombinant plasmid was induced by IPTG to express the fusion protein，which was identified by SDS-PAGE and Western blot with positive sera. The protein was purified and used as a diagnostic antigen for ELISA to test serum samples. Results There was no difference among the sequences of T.gondii GRA7 gene from different isolates. The recombinant plasmid pGEX-4T-1/GRA7 induced by IPTG was expressed in E.coli. It was a GST fusion protein and could react with human and rabbit positive sera analyzed by Western blot. Conclusion The GRA7 gene of T.gondii isolates is highly conservative. The GRA7 is expressed as a recombinant protein in Escherichia coli, which shows an immunoreactivity.

Key words: Toxoplasma gondii, Dense granule protein 7 (GRA7), Sequence analysis, Gene expression, immunoreactivity