The Escherichia coli cAMP receptor protein -: global transcriptional regulator

The Escherichia coli cyclic AMP receptor protein (CRP) plays a key role in the transcription regulation for more than one hundred genes, mainly involved in the catabolism of carbon sources other than glucose. The protein,is a homodimer and each monomer is folded into two distinct structural domains. CRP conformation and activity as a transcription factor are dependent upon cAMP. In response to cAMP binding the protein undergoes a conformational change that allows it to bind specific DNA sequences and interact with RNA polymerase. CRP in complex with cAMP regulates transcription initiation mainly as a sole activator or as a coactivator. Simple CRP-dependent promoters can be grouped into two classes according to the location of the target DNA site for CRP and the mechanism of transcription activation. At class I CRP-dependent promoters, the DNA site for CRP is located upstream of the core promoter. Transcription activation at class I CRP-dependent promoters involves a single protein-protein interaction between CRP and RNA polymerase. At class 11 CRP-dependent promoters, the DNA site for CRP overlaps the DNA site for RNAP and transcription activation involves three sets of protein-protein interactions between CRP and RNAP. At some CRP-dependent promoters the mechanism of transcription activation is more complex. Two or more CRP dimers or one CRP molecule and one or more molecules of other activators synergistically cooperate to activate transcription initiation.