Expression levels of transcription factors in Escherichia coli: growth phase- and growth condition-dependent variation of 90 regulators from six families

The expression pattern of the genome in Escherichia coli is controlled by regulating the utilization of a limited number of RNA polymerases between a total of 4600 genes on its genome. The distribution pattern of RNA polymerase on the genome changes after two steps of protein protein interaction with seven sigma subunits and about 300 transcription factors (TFs). Based on a systematic search for the regulation target promoters recognized by each TF, we propose two novel concepts: each IF regulates a number of target promoters; and each promoter is regulated by many TFs. In parallel, attempts have been made to determine the intracellular concentrations of all TFs using two systems: quantitative immunoblot analysis using TF-specific antibodies; and reporter assay of TF promoter activities. The direct measurement of TF protein level has so far been published for a set of 60 regulators with known functions. This study describes the determination of growth phase-dependent expression levels of 90 TFs using the reporter assay system. The translational fusion vector was constructed from the IF promoter sequence including an N-terminal proximal TF segment and the reporter GFP. At the beginning of cell growth, high-level expression was observed only for a small number of TFs. In the exponential phase, approximately 80% TFs are expressed, but the expressed TF species change upon transfer to the stationary phase. Significant changes in the pattern of IF expression were observed between aerobic and anaerobic conditions. The list of intracellular levels of TFs provides further understanding to the transcription regulation of the E. coli genome under various stressful conditions.