What is the role of cAMP in the CAP-cAMP complex?

cAMP plays a crucial role in the formation and function of the CAP-cAMP complex, particularly in the regulation of transcription in prokaryotes, such as E. coli. When glucose levels are low, cAMP levels rise, leading to the binding of cAMP to the catabolite activator protein (CAP). This binding causes a conformational change in CAP that enables it to bind more effectively to specific DNA sites upstream of promoters, forming the CAP-cAMP complex.

The resulting enhancement of CAP's ability to bind to DNA is key for promoting the transcription of genes involved in the metabolism of alternative sugars, primarily when glucose is scarce. This promotes the transcription of operons like the lac operon, allowing the cell to switch to using other energy sources effectively.

The other options do not accurately represent the role of cAMP in this context. For instance, the binding of CAP to DNA while in the CAP-cAMP complex is central to its function in transcription regulation, not degradation of DNA or enhancing inhibition of transcription. Therefore, the correct characterization of cAMP’s function within the CAP-cAMP complex is its facilitation of CAP binding to DNA.