In the E. coli lac operon, which condition gives the highest transcription of lacZYA?

Lactose present, glucose absent

A mutation in the lacI gene produces a repressor that cannot bind allolactose but can still bind the operator. What phenotype is expected for the lac operon?

Permanent repression even in the presence of lactose

In the ara operon, AraC can both repress and activate transcription. Which mechanism explains repression in the absence of arabinose?

AraC binds distant sites and forms a DNA loop that hinders transcription initiation

A point mutation changes the two adjacent Trp codons in the trpL leader peptide to Ala codons without altering the RNA sequences that form hairpins. What is the most likely effect under tryptophan starvation?

Increased attenuation, because ribosome no longer stalls specifically in response to low tryptophan

In a merodiploid E. coli strain with genotype I+ Oc Z+ / I+ O+ Z-, what will be the expression pattern of functional beta-galactosidase?

Constitutive, because Oc acts only in cis on the linked Z+ gene

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