What role does the catabolite activator protein play in the lac operon?

The catabolite activator protein (CAP), also known as cAMP receptor protein (CRP), plays a critical role in the regulation of the lac operon through its interaction with cyclic AMP (cAMP). When glucose levels are low, the concentration of cAMP increases, and this elevated cAMP binds to CAP. The cAMP-CAP complex then binds to a specific site on the promoter of the lac operon, facilitating the recruitment of RNA polymerase to the promoter and enhancing transcription of the genes necessary for lactose metabolism.

In conditions of low glucose and high lactose, the lac operon needs to be activated to allow the cell to utilize lactose as an energy source. The presence of lactose leads to the inactivation of the repressor protein, which normally blocks the transcription of the lac operon. With the repressor inactivated, and with the assistance of the cAMP-CAP complex, the transcription of the lac operon is significantly increased, allowing for the efficient metabolism of lactose.

Therefore, the correct role of CAP in the context of the lac operon is that it increases expression in low glucose and high lactose conditions. This mechanism exemplifies the intricate regulation of gene expression in prokaryotic systems and highlights the significance of environmental