What activates CAP DNA-binding activity in the context of the Lac operon?

The activation of CAP (catabolite activator protein) DNA-binding activity in the context of the Lac operon is primarily dependent on low glucose levels. When glucose levels are low, the concentration of cyclic AMP (cAMP) in the cell increases. cAMP then binds to CAP, leading to a conformational change that allows CAP to bind to the promoter region of the Lac operon. This binding enhances the transcription of genes involved in lactose metabolism by facilitating the binding of RNA polymerase to the promoter.

In essence, the presence of low glucose creates a situation where the cell requires alternative sources of energy, such as lactose. The interaction between cAMP and CAP, in this context, acts as a signal that triggers the expression of genes necessary for metabolizing lactose, showcasing how energy sources influence gene regulation in bacteria.

High lactose levels, high glucose levels, and low lactose levels do not promote the activation of CAP. High lactose actually leads to the inactivation of the repressor, allowing transcription to occur but does not activate CAP. High glucose levels result in low cAMP, which inhibits the activation of CAP. Low lactose levels do not support the expression of lac genes either, as they lead to repression rather than activation.