INTEGRATION HOST FACTOR IS REQUIRED FOR ANAEROBIC PYRUVATE INDUCTION OF PFL OPERON EXPRESSION IN ESCHERICHIA-COLI

The expression of the pyruvate formate-lyase gene (pfl) is induced by anaerobic growth, and this is increased further by growth in pyruvate. Previous work has shown that anaerobic induction is strongly dependen t on the activator FNR and partially dependent on a second transcripti on factor, ArcA, while pyruvate induction only required FNR. Anaerobic and pyruvate regulation both require the presence of a 5' nontranslat ed regulatory sequence which spans approximately 500 bp of DNA. A mobi lity shift assay was developed to identify proteins that bind to this regulatory region. Several binding activities were separated by hepari n agarose chromatography, and one of these activities was characterize d and shown to be integration host factor (IHF). Mobility shift and DN ase I footprinting experiments defined a single IHF binding site in th e pfl promoter-regulatory region. With pfl-lacZ fusions, it could be s hown that introduction of a himD mutation abolished pyruvate-dependent induction of anaerobic expression in vivo. The same result was observ ed when the pfl IHF binding site was mutated. In addition, the partial anaerobic induction of expression found in an fnr strain was complete ly blocked in an fnr himD double mutant and in an fnr IHF binding site double mutant. Taken together, these data suggest that IHF is necessa ry for both pyruvate induction and the anaerobic induction mediated by ArcA.