The H-NS protein modulates the activation of the ilvIH operon of Escherichia coli K12 by Lrp, the leucine regulatory protein.

The H-NS protein, the product of the hns gene, plays a central role in the cellular response of bacteria to environmental stresses such as modification of osmolarity and temperature. The leucine regulatory protein (Lrp) controls a wide array of operons both as an activator (e.g. ilvIH) and as a repressor. We demonstrate that H-NS can decrease the activity of Lrp in stationary phase and under conditions of high osmolarity. Strains containing hns mutations have higher levels of Lrp-activated ilvIH transcription, while strains carrying the hns+ allele on a pBR322 plasmid have lower activity of Lrp-directed ilvIH gene expression.