In vivo footprinting analysis of Lrp binding to the ilvIH promoter region of Escherichia coli.

An in vivo footprinting analysis of the ilvIH regulatory region of Escherichia coli showed that the transcription activator Lrp binds to six sites, scattered over 250 bp upstream of the transcriptional start point. When Lrp-mediated activation was impaired by the presence of exogenous leucine, only one promoter-distal site (site 2) was partially protected by Lrp binding. Equilibrium dialysis experiments showed the formation of an Lrp-leucine complex in vitro. These results suggest that leucine negatively affects ilvIH transcription because its interaction with Lrp reduces the efficiency of binding of the regulatory protein to the promoter region.