CRP and cAMP: Gene Regulation in E. coli

Allosteric Activation of CRP

• Inactive CRP protein is converted to active CRP protein by binding to cAMP
• cAMP binds to CRP, enabling it to bind to a special DNA sequence adjacent to the RNA polymerase binding site
• This activation allows RNA polymerase to bind to the lac operon

Cyclic AMP and Glucose

• In E. coli, ATP is converted to cAMP by adenylate cyclase
• As glucose levels drop, cAMP levels increase
• cAMP binds to CRP, leading to transcription activation

Positive Regulation of Transcription

• A bound activator (CRP-cAMP complex) facilitates transcription by binding to specific DNA sequences
• This type of regulation is seen in the lac operon, where CRP-cAMP complex binds to the lac promoter, enhancing transcription

Regulation of the lac Operon

• In the absence of lactose, the repressor is bound, inhibiting expression
• When lactose is present, the repressor dissociates, allowing transcription
• High glucose levels prevent CRP binding, dampening transcription
• Low glucose levels increase cAMP, leading to CRP binding and activation of transcription

lac Operon Structure

• The lac operon has an operator site where the lac repressor protein binds, preventing transcription
• The lac promoter has a CRP-binding site where the CRP-cAMP complex binds, enhancing transcription
• The lac mRNA contains the genetic code for the lac repressor protein

This quiz covers the role of cAMP and CRP in gene regulation in E. coli, including allosteric activation and transcription activation.