H-NS and Fis binding to E. coli K12. H-NS and Fis binding to E. coli K12

Among the most important regulators of gene expression in bacteria are 'nucleoid-associated proteins'. These proteins alter the topology of the bound DNA by bending, wrapping or bridging it, thus having multiple effects, including transcriptional regulation, on the bacterial cell. Among the best-studied nucleoid proteins are H-NS and Fis, which bind to specific sequences on the DNA. H-NS is a global repressor of gene expression. Fis alters the global conformation of the DNA by introducing branched structures in it; but its effect on gene expression on a genomic scale remains largely unclear.Several bacterial transcriptional regulators including H-NS and Fis have been studied using ChIP-chip. However, the higher resolution and dynamic range offered by ChIP-Seq have not been exploited for any bacterial species. By performing ChIP-Seq of these two proteins, we present the first such study in a bacterium. In addition to providing a proof-of-principle for the use of this technology for bacteria, we perform our study at multiple time-points during growth in rich medium, thus generating new insights into how these proteins function under different cellular conditions. Further, by analysing our data in conjunction with newly-generated gene expression and RNA polymerase-chromosome interaction data we provide new interpretation of the genome-scale patterns of the interactions of these proteins to the DNA.