In spite of its name, catabolite repression is a type of positive control in the lac operon. CAP, complexed with cAMP, binds to a site near the promoter and stimulates the binding of RNA polymerase. Cellular levels of cAMP in the cell are controlled by glucose; a low glucose level increases the abundance of cAMP and enhances the transcription of the lac structural genes.
www.whfreeman.com/pierce Information on CAP control and the binding of CAP to DNA
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