You are characterizing an operon that demonstrates both inducible negative regulation as well as positive regulation. Under what conditions will you see the highest levels of transcription?

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To understand where transcription is maximally high for an operon that shows both inducible negative regulation and positive regulation, we need to consider what each component does.
Option 1: 'when the activator is bound to the repressor' suggests a direct interaction between activator and repressor that alters transcription. In classical models, the binding relationship described here does not directly describe promoter binding or operator control, so this option misstates the mechanism and would not reliably yield the highest transcription.
Option 2: 'when the activator is bound to the promoter region and the repressor is bound to the corepressor' combines accurate placement of the activator but uses 'corepressor' in a way that does not match the usual inducer/repressor dynamics of inducible systems. Corepressors are part of some regulatory schemes, but in the typical inducible negative regulation framework, the key factor is the inducer binding to the repressor, not a separate corepressor, so this option is biologically inconsistent with the described system.
Option 3: 'when the activator is bound to the promoter region and the repressor is bound to the operator' posits both an activator at the promoter and a repressor bound to the operator. If the repressor is bound to the operator, transcription would be blocked despite an activator at the promoter, so this scenario would not yield the highest transcription.
Option 4: 'when the activator is bound to the promoter region and the repressor is bound to the inducer' aligns with the expected synergistic effect: the activator at the promoter boosts transcription via positive regulation, while the inducer binding to the repressor inactivates it, relieving negative repression. With the repressor inactive and the activator present at the promoter, transcription would reach its peak levels.
In summary, the first option mischaracterizes the regulatory interactions, the second option muddles the core regulatory components using nonstandard terminology, the third option creates a conflicting state where the repressor would still block transcription, and the fourth option coherently combines activator-driven activation with inducer-mediated derepression to produce the highest transcription.

W25 BIOL D006B 01Y Cell & Molecular Biology Lecture Exam 2

You are characterizing an operon that demonstrates both inducible negative regulation as well as positive regulation. Under what conditions will you see the highest levels of transcription?

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