Final answer:
Cyclic AMP (cAMP) is involved in catabolite repression by binding to catabolite activator protein (CAP) and enhancing the transcription of genes required for using alternate sugar sources in the absence of glucose.
Step-by-step explanation:
Cyclic AMP (cAMP) plays a crucial role in catabolite repression. When glucose levels are low, cAMP levels rise in the cell. The increased cAMP binds to the catabolite activator protein (CAP), which then binds to the promoter region of the genes that are necessary to use alternative sugar sources. This interaction increases the binding ability of RNA polymerase to the promoter region and enhances the transcription of these genes, leading to higher levels of enzymes that facilitate the use of lactose as an energy source.