Catabolite Activator Protein

Encyclopedia : C : CA : CAT : Catabolite Activator Protein

Catabolite Activating Protein or CAP binds to DNA more tightly in the presence of cAMP (cyclic AMP). CAP has a characteristic helix-turn-helix structure which allows it to bind to successive major grooves on DNA. The two helixes are reinforcing each causing a 43° turn in the structure so overall causing a 94° degree turn in the DNA. This opens the DNA molecule up, allowing RNA polymerase to bind. CAP is involved in repressing the expression of the lac operon when glucose is present. This inhibition, called catabolite repression, reflects the greater simplicity with which glucose may be metabolized in comparison to lactose. The cell "prefers" glucose, and if it is available, the lac operon is not activated, even when lactose is present.

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