For the lac genotypes shown in the following table, predict whether the structural genes (Z) are constitutive, permanently repressed, or inducible in the presence of lactose. Genotype Constitutive Repressed Inducible I⁺O⁺Z⁺ x I⁻O⁺Z⁺ I⁻OᶜZ⁺ I⁻OᶜZ⁺/F'O⁺ I⁺OᶜZ⁺/F'O⁺ IˢO⁺Z⁺ IˢO⁺Z⁺/F'I⁺

For the genotypes and conditions (lactose present or absent) shown in the following table, predict whether functional enzymes, nonfunctional enzymes, or no enzymes are made.

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The locations of numerous lacI⁻ and lacIˢ mutations have been determined within the DNA sequence of the lacI gene. Among these, lacI⁻ mutations were found to occur in the 5′-upstream region of the gene, while lacIˢ mutations were found to occur farther downstream in the gene. Are the locations of the two types of mutations within the gene consistent with what is known about the function of the repressor that is the product of the lacI gene?

The CAP binding site in the lac promoter is the location of positive regulation of gene expression for the operon. Identify what binds at this site to produce positive regulation, under what circumstances binding occurs, and how binding exerts a positive effect.

What role does cAMP play in transcription of lac operon genes? What role does CAP play in transcription of lac operon genes?

What properties demonstrate that the lac repressor is a protein? Describe the evidence that it indeed serves as a repressor within the operon system.

How would a cap⁻ mutation that produces an inactive CAP protein affect transcriptional control of the lac operon?

Predict the effect on the inducibility of the lac operon of a mutation that disrupts the function of:

(a) The CRP gene, which encodes the CAP protein

(b) The CAP-binding site within the promoter.