Genetic Regulation and the Lactose Operon

ID #1424

My question is concerning lac operon expression. What's clear to me is the fact that the lifting of negative regulation allows for some (not maximum) expression of the lac operon gene. However, maximum expression is only achieved when cAMP is present (therefore glucose absent) and bound to the CRP proteins. My question is whether or not CRP is present in the absence of cAMP. If it is, then in what form? (Is it bound to the promoter region or simply present in the general vicinity?)

Great observation. CRP is used to help regulate more operons in E. coli than just the lac operon, so it can't spend all its time "hanging out" at the lac operon just in case it's needed. So it will be constitutively expressed, but just floating around in the cytoplasm "looking" for some cAMP to pair up with.

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