Molecular cloning and expression of a T-cell stimulating membrane protein of Francisella tularensis

The isolation and expression in Escherichia coli of a gene encoding a T-cell stimulating 17 kiloDalton (kDa) membrane protein of Francisella tularensis is described. A genomic library of DNA from the live vaccine strain LVS of F. tularensis was constructed in the E. coli expression vector phage lambda gt11. The library was probed with antibodies directed against the 17 kDa protein. One recombinant phage was isolated, containing a 2.8 kilobase (kb) DNA insert. The insert was cleaved and a resulting 1.2 kb fragment was found to express the 17 kDa protein. The 1.2 kb fragment was inserted in the high copy number plasmid pUC18 and expressed in E. coli. Membrane preparations of these bacteria induced a response in T cells from F. tularensis-primed individuals but not in T cells from non-primed individuals. The cloned gene may become useful in studies on host interaction with F. tularensis and enable a precise identification of bacterial structures involved in the T-cell response.