Inducers catabolite activator protein

Zinkel, S. S., and Crothers, D. M. (1990). Comparative gel electrophoresis measurement of the DNA bend angle induced by the catabolite activator protein. Biopolymers 29, 29—38. 

Some proteins activate transcription by directly contacting RNA polymerase. For example, cyclic AMP, a hunger signal, stimulates the transcription of many catabolic operons by binding to the catabolite activator protein. The binding of the cAMP—CAP complex to a specific site in the promoter region of an inducible catabolic operon enhances the binding of RNA polymerase and the initiation of transcription. 

Catabolite Activation In bacteria, a transcriptional control system that induces the synthesis of enzymes for the catabolism of energy substrates other than glucose when glucose levels are low. It involves an activator protein, CRP, that binds cyclic AMP under conditions of low glucose this complex then binds to DNA sites and promotes transcription of the appropriate genes. 

Although the inducer causes the lacl repressor protein to dissociate from the operator, the glucose will lead to a low level of cAMP (low adenylate cyclase activity). As the CAP-cAMP complex dissociates, the CAP protein will leave the CAP site. This will repress transcription of lacZ, lac Y, and lac A (catabolite repression). 

---