Identification of a heat-modifiable protein of Francisella tularensis and molecular cloning of the encoding gene.

As an initial step in defining the constituents of the outer surfaces of Francisella tularensis, membrane fractions were prepared, and the immunoreactivity of constituents examined by Western immunoblotting. One protein, thought to be an outer membrane protein, was found to be heat and beta-mercaptoethanol (2-ME)-modifiable and was named FopA. This protein migrates at an apparent molecular weight of 34 kilodaltons (kDa) when cell extracts are solubilized below 80 degrees C, but migrates as a doublet of 41- to 43-kDa when cell extracts are solubilized at 95 degrees C. A cosmid bank was constructed and two recombinants were found to express FopA. The recombinant FopA was also heat and beta-mercaptoethanol modifiable and was found to localize in the outer membrane of Escherichia coli.