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| Modern Genetic Analysis Chapter 14. Regulation of Gene Transcription Regulation of the Lactose System Figure 14-6. Catabolite control of the lac operon. The operon is inducible by lactose to the maximal levels when cAMP and CAP form a complex. (a) Under conditions of high glucose, a glucose breakdown product inhibits the enzyme adenylate cyclase, preventing the conversion of ATP into cAMP. (b) Under conditions of low glucose, there is no breakdown product, and therefore adenylate cyclase is active and cAMP is formed. (c) When cAMP is present, it acts as an allosteric effector, complexing with CAP. (d) The cAMPCAP complex acts as an activator of lac operon transcription by binding to a region within the lac promoter. (CAP = catabolite activator protein; cAMP = cyclic adenosine monophosphate.)

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