A new aspect of transcriptional control of the Escherichia coli crp gene: positive autoregulation.

Transcription of the Escherichia coli crp gene is negatively regulated by CRP-cAMP that binds to a specific site located downstream of the crp promoter. A second binding site for CRP-cAMP (CRP site II) exists upstream of the crp promoter. Using an in vitro transcription assay, we have demonstrated that CRP-cAMP activates transcription of crp in certain conditions. A promoter which carries an altered CRP-binding site II is no longer activated by CRP-cAMP, indicating that CRP site II mediates the activation of crp transcription. The concentrations of cAMP that are required for positive autoregulation are higher than those for negative autoregulation. Evidence for positive and negative autoregulation in vivo is presented by a quantitative S1 nuclease analysis.