CAMP is cyclic adenosine monophosphate, and CAP is catabolite gene activation protein (CAP), which has no effect on transcription, but only acts after CAMP binds to it, controlling the binding of RNA Pol to the promoter on lactose operon. The region of lactose operon -70 ~-50 is cap site I, while -50 ~-40 is cap site II. Firstly, cAMP-CAP complex binds to CAP site I and promotes the binding of another molecule, cAMP-CAP, to CAP site II. They all promote the combination of RNA Pol and promoter -35 region, so that transcription can be carried out quickly.