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Polymerase chain reaction (PCR) was used to generate DNA encoding a 60 kDa stress protein of Mycobacterium paratuberculosisusing primers complementary to sequences at the 5′ and 3′ ends of 60 kDa stress protein genes (encoding the ‘65 kDa antigens’) of M. lepraeand M. tuberculosis.The predicted PCR product of 1.8kb contained the entire coding sequence of an M. paratuberculosis60kDa stress protein, with non-coding regions of 124bp and 1bp at the 5′ and 3′ ends, respectively. DNA encoding the entire ORF for the 60kDa stress protein, as well as thrombin and Factor Xa proteolytic cleavage sites, was ligated into the bacterial expression vector pGEX-2T and used to transform Escherichia colistrain JM83. Transformed bacteria, induced by IPTG, expressed an 85 kDa fusion protein comprising glutathione S-transferase (GST) and M. paratuberculosis60 kDa stress protein. This fusion protein was purified by adsorption to glutathione-agarose beads and shown to cross-react in Western blot analysis with an anti-mycobacterial 60 kDa stress protein monoclonal antibody. Recombinant M. paratuberculosis60 kDa stress protein was liberated from GST by proteolytic cleavage with either thrombin or Factor Xa enzyme. Authenticity of liberated recombinant stress protein was confirmed by N-terminal amino acid sequencing.
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