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Transcription and Translation · USMLE Step 1

What happens to the σ factor of bacterial RNA polymerase after initial transcription initiation?

  1. It stays bound to the core polymerase throughout the elongation phase
  2. It dissociates after about 10 nucleotides have been synthesized
  3. It is rapidly degraded by cellular proteases
  4. It is converted into a transcription termination factor
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Correct answer: It dissociates after about 10 nucleotides have been synthesized

After initiation and synthesis of the first ~10 nucleotides, the σ factor dissociates from the bacterial core RNA polymerase, which then continues elongation on its own. The σ factor is recycled, not degraded, and does not become a termination factor.

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