Rho is a member of the family of hexameric ATP-dependent helicases. Each subunit has an RNA-binding domain and an ATP hydrolysis domain.

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#Unit 2. Cellular Organization

Promoter mutations are also cis-acting. If they prevent RNA polymerase from binding at P-lac, the structural genes are never transcribed.

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#Unit 2. Cellular Organization

Mutants that cannot be expressed at all are called uninducible. Mutants that are continuously expressed are called constitutive mutants.

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#Unit 2. Cellular Organization

“Cryptic mutants” of lac operon make b-galactosidase but still could not grow on lactose means they are essentially Y-

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#Unit 2. Cellular Organization

Catabolite repression is exerted through a second messenger called cyclic AMP (cAMP) and the positive regulator protein called the catabolite repressor protein (CRP), a dimer.

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#Unit 2. Cellular Organization

CAP–cAMP complex stimulates transcription of the lac operon by binding to an activator-binding site adjacent to the promoter and helping RNA polymerase bind to the promoter.

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#Unit 2. Cellular Organization