Integration host factor bends the DNA in the Escherichia coli ilvBN promoter region.

Integration host factor (IHF) of Escherichia coli is a site-specific DNA binding protein involved in a wide variety of physiological activities in E. coli and its phages and plasmids. We have previously found that IHF binds specifically to a site just upstream from the ilvBN promoter and strongly decreases transcriptional pausing and termination in the ilvBN leader. In this work we show by gel retardation analysis that IHF binds to bent ilvBN DNA and greatly enhances the bend located within or near the IHF binding site. These data are consistent with the hypothesis that IHF-induced alterations in the conformation of ilvBN promoter-leader DNA is a key to its antitermination activity in this system.