8. Which one of the following ensures stable binding of RNA polymerase at the promoter site?
(1) DNA photolyase      (2) Sigma factor
(3) DNA glycosylase (4) Rec A

Which one of the following ensures stable binding of RNA polymerase at the promoter site?

1. DNA photolyase

2. Sigma factor

3. DNA glycosylase

4. Rec A

Correct Answer: (2) Sigma factor

Explanation:

Role of Sigma Factor in Bacterial Transcription:

• In prokaryotes like Escherichia coli, RNA polymerase cannot recognize promoter sequences on its own.

• The sigma (σ) factor binds to the core RNA polymerase enzyme to form the holoenzyme.

• This holoenzyme can now specifically recognize and bind to the -35 and -10 consensus sequences of a promoter region.

Stable Promoter Binding:

• Sigma factor ensures that RNA polymerase binds accurately and stably to the promoter.

• It enables closed complex formation, which transitions into an open complex where DNA is unwound for transcription to begin.

• Once transcription initiates, the sigma factor is released.

Why Other Options Are Incorrect:

Key Concept Recap for CSIR NET:

CSIR NET Preparation Tip:

• Remember: The sigma factor is essential for initiating transcription, not for elongation.

• Focus on sigma factor subtypes like σ⁷⁰ (housekeeping), σ³² (heat shock), etc.

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