Characterization of native and recombinant 75-kilodalton immunogens from Chlamydia trachomatis serovar L2

A 75-kilodalton (kDa) immunogen from Chlamydia trachomatis serovar L2 was characterized. The 75-kDa protein was localized in the cytoplasm of chlamydiae and was shown to be a protein synthesized early in the developmental cycle of chlamydiae. A gene library was made by the recombinant DNA technique, using the expression vectors pEX1, pEX2, and pEX3. From this library one clone was found which reacted with a monoclonal antibody against the 75-kDa immunogen of C. trachomatis. The 75-kDa protein produced by the recombinant Escherichia coli was expressed independently of the promoter for the hybrid protein cro-betagalactosidase. Thus it is not produced as a fusion protein. Epitope mapping of the 75-kDa protein from C. trachomatis L2 and from the recombinant E. coli performed by Staphylococcus aureus V8 protease digestion showed that the two proteins are identical. Furthermore, patient sera reacted with both proteins.