10. In prokaryotes which subunit of RNA polymerase is released after transcription initiation process?
(1) α            (2) β
(3) β’                (4) σ

MCQ:

In prokaryotes, which subunit of RNA polymerase is released after the transcription initiation process?

1. α

2. β

3. β′

4. σ

Correct Answer: (4) σ

Explanation:

RNA Polymerase Holoenzyme in Prokaryotes:

• Core enzyme = α₂ββ′ω

• Holoenzyme = Core enzyme + σ-subunit

Function of the σ-Subunit (Sigma Factor):

• The σ-subunit is essential for:

  • Promoter recognition

  • Binding of RNA polymerase to the -35 and -10 consensus sequences

• Once transcription initiates and the RNA chain begins to elongate, the σ-subunit is no longer needed.

What Happens After Initiation?

• The σ-subunit is released after about 8–10 nucleotides of RNA are synthesized.

• The core enzyme (α₂ββ′ω) continues the process of RNA chain elongation.

Why Other Options Are Incorrect:

• σ-subunit = Initiates transcription

• Released after promoter clearance

• Core polymerase = responsible for elongation and termination

CSIR NET Strategy Tip:

• Focus on which subunit does what in transcription:

  • σ = recognition and release

  • β & β′ = core catalytic activity

  • α = structural role

• This is a high-frequency MCQ topic in Life Sciences Section B & C.

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