Ubiquitous promoter-localization of essential virulence regulators in Francisella tularensis

The coordinate action of three transcription factors, MglA, SspA, and PigR, are required for virulence of the Gram-negative bacterium Francisella tularensis. MglA and SspA function as a heterodimer and contact RNA polymerase (RNAP). PigR is a putative DNA binding protein and requires interaction with the MglA-SspA complex to control gene expression. We used ChIP-Seq to identify where MglA, SspA, and PigR are found in relation to the genes they are known to regulate. To identify promoter regions of regulated and non-regulated genes, we performed ChIP-Seq on the ß' subunit of RNA polymerase (RNAP) in the presence of rifampicin, a small molecule which traps RNAP at promoters. We also identified promoter regions by performing ChIP-Seq on the two s subunits in F. tularensis LVS, s70 and s32. Additionally, we performed ChIP-Seq on a putative site-specific DNA binding protein, HipB, to demonstrate the specificity of our findings. We determined that MglA, SspA, and PigR are found at virtually all promoters. Additional experiments demonstrate that PigR requires the presence of MglA to specifically associate with promoter regions.