Over Expression of the Ag85B Gene of Mycobacterium tuberculosis in Escherichia coli

Objective To obtain recombinant Ag85B protein in large quantities by stable expression of the gene encoding for Ag85B antigen of Mycobacterium tub erculosis in E.coli. Methods Expression plasmid was constructed with DNA recombi nant technique. Positive clones were screened using doubled digestion and polyme rase chain reaction. Recombinant plasmid was transformed into E.coli. Then E.col i carrying recombinant plasmid were induced to express Ag85B. The expression of Ag85B antigen was identified by SDS-polyacrylamid gel electrophoresis (PAGE). S tained gel was scanned to detect expression level of recombinant antigen. Result s Gel stained with Coomassie blue G 250 showed that the induced E.coli carrying recombinant plasmid could produce Ag85B protein at high level, about 33%to 38% of total cellular proteins. The combinant Ag85B antigen existed mostly in inclus ion bodies. Conclusion Recombinant Ag85B antigen of Mycobacterium tuberculosis w as espressed in high level as inclusion bodies in E.coli.