Cloning and characterization of the gene encoding Pasteurella haemolytica FnrP, a regulator of the Escherichia coli silent hemolysin SheA

A Pasteurella haemolytica Al gene was identified from a recombinant library clone that expressed hemolysis in host Escherichia coli cells. The gene, d esignated fnrP, had sequence identity to E. coli fnr, a global transcriptio nal regulator of genes required for conversion to anaerobic growth. FnrP co mplemented anaerobic deficiencies of a fnr-null mutant strain of E. coli an d increased expression of the Fnr-dependent, anaerobic terminal reductase g ene, frdA, FnrP was purified, identified by immunoblotting, and shown to be nonhemolytic, When FnrP was expressed in E. coli Delta sheA, a null mutant of the cryptic hemolysin SheA, the transformants were nonhemolytic, indica ting that FnrP activates this silent hemolysin.