Expression of the Chlamydia trachomatis major outer membrane protein-encoding gene in Escherichia coli: role of the 3′ end in mRNA stability

The major outer membrane protein (MOMP)-encoding gene (ompl) of Chlamydia trachomatis has been cloned into Escherichia coli and partially sequenced. This recombinant gene expresses a full-length 40-kDa product, which is recognized by a monoclonal antibody directed against the species-specific epitope of MOMP. The recombinant ompl is expressed in either insertion orientation, indicating that it utilizes its own promoter system. The endogenous ompl promoter possesses a relatively low activity despite the high level of MOMP expression. Deletion of a 520-bp fragment at the 3′ end encoding 39 amino acids (aa) at the C terminus and the remainder of the noncoding region leads to a significant decrease in mRNA stability and loss of protein synthesis. When the MOMP-encoding plasmid was introduced into E. coli minicells, it expressed 40- and 43-kDa proteins; however, inhibition of post-translational processing by ethanol revealed only a 43-kDa protein. These data indicate that the unprocessed ompl gene product contains a 22-aa leader sequence which is cleaved during translocation to the outer membrane, to yield a processed 40-kDa protein. The recombinant MOMP was localized to the outer membrane E. coli fraction, comparable to the location of the native C. trachomatis protein.