Mapping E. coli RNA polymerase and associated transcription factors and identifying promoters genome-wide.

The ability to examine gene regulation in living cells has been greatly enabled by the development of chromatin immunoprecipitation (ChIP) methodology. ChIP captures a snapshot of protein-DNA interactions in vivo and has been used to study interactions in bacteria, yeast, and mammalian cell culture. ChIP conditions vary depending upon the organism and the nature of the DNA-binding proteins under study. Here, we describe a customized ChIP protocol to examine the genome-wide distribution of a mobile DNA-binding enzyme, Escherichia coli RNA Polymerase (RNAP) as well as the factors that dynamically associate with RNAP during different stages of transcription. We describe new data analysis methods for determining the association of a broadly distributed DNA-binding complex. Further, we describe our approach of combining small molecules and antibiotics that perturb specific cellular events with ChIP and genomic platforms to dissect mechanisms of gene regulation in vivo. The chemical genomic methods can be leveraged to map natural and cryptic promoters and transcription units, annotate genomes, and reveal coupling between different processes in regulation of genes. This approach provides the framework for engineering gene networks and controlling biological output in a desired manner.