Integration host factor is a transcriptional cofactor of pilE in Neisseria gonorrhoeae

Integration host factor (IHF) is a small, heterodimeric DNA-binding protein with pleiotropic function. IHF was purified to apparent homogeneity from Neisseria gonorrhoeae. Gel-retardation assays demonstrated binding of IHF to the pilE promoter region. The IHF-binding site was identified by DNase I protection assays and mapped proximal to three previously defined pilE promoters. Removal of the putative IHF-binding domain from pilE promoter DNA negated retardation of the DNA fragment when assessed by gel-shift analysis. Kleinschmidt electron microscopy showed pronounced kinking of pilE promoter DNA following incubation with IHF. Isogenic N. gonorrhoeae strains were constructed that contained either a wild-type pilE locus or a deleted pilE locus where the IHF-binding domain was removed. Primer-extension analysis and Northern blotting of total gonococcal RNA showed that in the absence of IHF binding at the pilE promoter, transcription was reduced 10-fold. Together, these data indicate that IHF is a transcriptional co-activator of pilE.