Abstract: Objective To express phoS2 in Escherichia coli，purify the recombinant protein，preliminary evaluate its antigenicity and specificity by Western blot. MethodsExpression plasmid of phoS2 was constructed with DNA recombinant technique. Positive clones were chosen using emzyme digestion and polymerase chain reaction. Recombinant plasmid was transformed into E.coli. Then phoS2 was induced to express. The expression of phoS2 was identified by SDS-polyacrylamid gel electrophoresis (SDS-PAGE); the recombinant protein was purified; the antigenicity and specificity of phoS2 protein was analyzed by Western blot. ResultsphoS2 was highly expressed in E.coli，the amount of phoS2 protein in E.coli BL21 occupied more than 40% of total bacterial proteins. Purified protein could react strongly with serum samples from the patients with tuberculosis, but could not react with serum samples from healthy control. ConclusionThe recombinant phoS2 protein was expressed mostly in inclusion body form in E.coli. The Results indicated that the recombinant phoS2 antigen showed higher antigenic specificity and immunoreactivity，had potential application value in diagnosis of tuberculosis.

Key words: Escherichia coli, Phosphate transport proteins, Recombinant proterins