Genetic regulation in lysogeny: Which phage-encoded protein maintains the prophage in a dormant state by preventing lytic gene expression?

Introduction / Context:
Temperate phages such as lambda rely on a regulatory protein to silence lytic genes while integrated into the host genome. This protein binds operator sequences to block transcription from lytic promoters, maintaining lysogeny and conferring immunity to superinfection by related phages.

Given Data / Assumptions:

• Repressors are DNA-binding proteins that recognize operator sites.
• They prevent RNA polymerase from initiating lytic transcription.
• Terminology distinguishes proteins (repressor) from DNA elements (operator, promoter).

Concept / Approach:
In phage lambda, the CI repressor binds operator sites O_L and O_R, shutting down lytic promoters P_L and P_R. As long as repressor levels are maintained, the prophage remains quiescent. Stress-triggered repressor cleavage leads to induction and lytic growth.

Step-by-Step Solution:
Identify the functional role: block lytic transcription. Match function to protein: repressor. Exclude DNA elements (operator, promoter) and nonspecific terms (enhancer). Recognize integrase is needed for integration, not maintenance via repression.

Verification / Alternative check:
Genetic experiments show loss of repressor results in spontaneous induction; overexpression stabilizes lysogeny.

Why Other Options Are Wrong:
Operator and promoter are DNA sequences; enhancer is a eukaryotic regulatory concept; integrase catalyzes integration but does not suppress lytic transcription.

Common Pitfalls:
Confusing the repressor (protein) with operator (binding site) in terminology questions.

Final Answer:
Repressor.