Stable Binding of RNA Polymerase to Promoter

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

admin
May 27, 2025
13 Comments

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?

DNA photolyase
Sigma factor
DNA glycosylase
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:

Option	Function	Relevance
DNA photolyase	Repairs UV-induced thymine dimers	Unrelated to transcription
DNA glycosylase	Involved in base excision repair	Not involved in promoter recognition
Rec A	Facilitates homologous recombination	No role in RNA polymerase binding

Key Concept Recap for CSIR NET:

Component	Function
RNA Polymerase Core (α₂ββ′ω)	Catalyzes RNA synthesis
Sigma Factor (σ)	Guides RNA polymerase to promoter, ensures stable and specific binding

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.