In addition, an A-T rich region is found upstream of this sequence, strongly suggesting a role for these sequences in the binding of the IHF protein. Mobility shift assays with mutant probes clearly demonstrated a role for these residues in the P phtD -IHF interaction. Similarly, our proposal for the requirement of a change in the DNA structure Proteasome inhibitor for IHF binding to the phtD operon is somewhat supported

by various reports which demonstrate that besides the interaction with consensus sequences, the IHF protein requires a curved DNA structure for binding [38]. The IHF protein contributes in an important way to the function of a wide variety of macromolecular processes 3-MA in vitro in bacteria and is recognized as a global regulation factor in the transcription of many genes. IHF can alter gene expression in a number of ways, including positive and negative effects on transcription, and its role as a regulator of virulence gene expression has increasingly been determined [39, 42]. The role of IHF protein in regulating phtD operon expression was examined through the analysis of a phtD::gfp

transcriptional fusion in an E. coli K12 ihfA – mutant background, which clearly showed higher transcriptional activity than that observed in the wild type background. This activity significantly decreases when the ihfA – mutant strain is complemented in trans with the ihfA gene of P. syringae pv. phaseolicola NPS3121, suggesting that the IHF protein has a negative effect on the expression of the phtD operon in E. coli. Because some reports have demonstrated that the E. coli IHF protein can functionally replace IHF proteins of some Pseudomonas Amino acid species, and since this protein is not modulated by interactions with inducer or co-repressor molecules, as are most transcription factors [33, 35], we propose that the IHF protein also exerts a negative effect on P. syringae pv. phaseolicola

NPS3121 phtD operon expression. IHF has been shown to act as a negative regulator through several mechanisms. In some cases, IHF seems to act as a classical repressor by binding to DNA within the RNA polymerase recognition site and excluding the polymerase from the promoter. IHF may also act indirectly as a repressor, ABT-737 datasheet collaborating with a gene-specific repressor or obstructing the binding of an activator. Alternatively, IHF can repress transcription in concert with other nucleoid proteins and global or gene-specific transcriptional regulators to create a higher-order nucleoprotein complex that forms an inhibitory promoter architecture [35, 37, 42]. The way in which IHF could act to repress the phtD operon is unknown, although according to the position of the predicted IHF binding site (-64 to -44), its role as a classical repressor may be dismissed.