Abstract
Recent research has indicated the presence of highly protein occupied, transcriptionally silent regions of bacterial genomes which show functional parallels to eukaryotic heterochromatin. We utilized an integrative approach to track chromatin structure and transcription in Escherichia coli K-12 across a wide range of nutrient conditions. In the process, we identified multiple loci which act similarly to facultative heterochromatin in eukaryotes, normally silenced but permitting expression of genes under specific conditions. We also found a strong enrichment of small regulatory RNAs (sRNAs) among the set of differentially expressed transcripts during nutrient stress. Using a newly developed bioinformatic pipeline, the transcription factors (TFs) regulating sRNA expression were bioinformatically predicted, with experimental follow-up revealing novel relationships for 45 sRNA-TF candidates. Direct regulation of sRNA expression was confirmed by mutational analysis for five sRNAs of metabolic interest: IsrB (also known as AzuCR), CsrB and CsrC, GcvB, and GadY. Our integrative analysis thus reveals additional layers of complexity in the nutrient stress response in E. coli and provides a framework for revealing similar poorly understood regulatory logic in other organisms.