Autoregulation of the Escherichia coli crp gene: CRP is a transcriptional repressor for its own gene

The restriction fragments carrying the region preceding the Escherichia coli crp structural gene were transcribed. The 5' end of the crp mRNA was determined by RNAase partial digestion and S1 digestion methods. Thus the crp gene has been shown to possess a 167 bp leader. CRP-cAMP specifically prevents the crp transcription. In other words, the crp gene is regulated autogenously. DNAase foot-printing studies indicated that CRP-cAMP binds to the crp gene at positions +26 to +67. This region exhibits a striking sequence homology to the CRP-binding sites in other genes. CRP and RNA polymerase bind to the crp regulatory region simultaneously. These results suggest a different mechanism for transcriptional repression of the crp gene by CRP-cAMP from that of a typical operator-repressor model.