9. Mutation in which subunit of RNA polymerase holoenzyme would have defect in correct initiation of transcription?
(1) α subunit (2) β subunit
(3) β’ subunit (4) σ-subunit
Mutation in which subunit of RNA polymerase holoenzyme would result in a defect in the correct initiation of transcription?
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α subunit
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β subunit
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β′ subunit
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σ-subunit
Correct Answer: (4) σ-subunit
Explanation:
Structure of Prokaryotic RNA Polymerase Holoenzyme:
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Core enzyme: α₂ββ′ω
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Holoenzyme = Core enzyme + σ-subunit
Role of σ-subunit (Sigma Factor):
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The σ-subunit is crucial for the initiation of transcription.
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It guides the core RNA polymerase to the specific promoter sequences (−35 and −10 regions).
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Without the σ-subunit, the polymerase cannot recognize the promoter → initiation fails.
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Once transcription starts, the σ-factor usually dissociates from the complex.
Why Other Options Are Incorrect:
| Subunit | Function | Role in Initiation |
|---|---|---|
| α | Enzyme assembly & promoter interaction support | Not directly responsible for promoter recognition |
| β | Catalysis of RNA chain elongation | Core enzymatic function, not initiation |
| β′ | DNA binding and clamp function | Structural, but not specific to initiation |
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α subunit:Two copies (αI and αII) of this subunit are involved in the assembly of the core RNA polymerase enzyme and contribute to promoter recognition.
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β subunit:This is the second largest subunit and forms part of the active catalytic site responsible for RNA synthesis.
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β’ subunit:This is the largest subunit and also contributes to the active catalytic site, essential for RNA polymerization.
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ω subunit:This is the smallest subunit and facilitates the assembly of the RNA polymerase enzyme.
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Sigma factor (σ):This factor is crucial for recognizing specific promoter sequences on the DNA template, directing the binding of the core enzyme to the promoter, and initiating transcription.
Conclusion:
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The σ-subunit ensures that transcription begins at the right site by recognizing the promoter.
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Mutation in this subunit → transcription initiation failure.
CSIR NET Takeaway:
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Know the roles of RNA polymerase subunits:
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σ-subunit = promoter recognition
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β & β′ = catalytic core
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α = structural and regulatory support
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Learn Efficiently with Let’s Talk Academy
-
Expert-led classes on RNA polymerase structure and function
-
Practice with PYQs and mock tests focused on transcription regulation
-
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37 Comments
Rani Sharma
May 28, 2025✅✅
Anita Choudhary
May 28, 2025✅👍
Suman bhakar
May 28, 2025✅✅
Ujjwal
May 28, 2025Done
Krishana
May 28, 2025Done 👍
Pallavi gautam
May 28, 2025Yess✅
Arushi
May 28, 2025👍☑️
Beena Meena
May 28, 2025Done
Shalu Choudhary
May 28, 2025✔️✔️
Monu
May 29, 2025👍👍
Bhanwar Jaat
May 29, 2025Wow
Priyam choudhary
May 29, 2025Done
Prami Masih
May 29, 2025Done sir ji 👍
Shreeji Charan
June 1, 2025👍
Kirti Agarwal
October 26, 2025Sigma subunit
Santosh Saini
October 26, 2025Sigma subunit ensure that transcription begins at the right site by recognising the promoter and sigma factor is a transcription initiation factor
Bhawna Choudhary
October 28, 2025Sigma subunit
Sonal Nagar
November 2, 2025Option 4
Heena Mahlawat
November 3, 2025Sigma subunit
Roopal Sharma
November 3, 2025Sigma unit ensure that transcription begins .
Pooja
November 3, 2025Option 4 is correct
Sneha kumawat
November 3, 2025Sigma subunit
Divya rani
November 3, 2025Sigma subunit of holoenzyme is crucial for transcription initiation in prokaryotes because it has recognition power for promotor if it is mutated then it can not recognise the promotor so RNA polymerase can not bind at promotor so no transcription.
Samiksha bajiya
November 3, 2025Sigma factor is a transcription factor crucial for recognizing specific promoter sequences on the DNA template directing the binding of core enzyme to promoter
Anurag Giri
November 3, 2025The option 4 is correct This factor is crucial for recognizing specific promoter sequences on the DNA template, directing the binding of the core enzyme to the promoter, and initiating transcription
Mohd juber Ali
November 3, 20251 Core pol = alpha ,beta ,beta’ and omega
2 holo enzyme is = sigma subunit + core pol.
Tc factor increase the affinity of core enzyme towards m rna so pairnig and closed complex dna not melt , rho independent
So mutation in sigma sub unit initiation of Tc would have defect
Priya dhakad
November 3, 2025Sigma subunit of holoenzyme is crucial for transcription initiation in prokaryotes becoz, it has recognition power for promotor if mutation in this subunit so transcription initiation failure .
Dipti Sharma
November 3, 2025The sigma subunit is crucial for the initiation of transcription , mutation in sigma mislead the RNA pol. Nd transcription interrupts.
Sneha kumawat
November 3, 2025The Sigma is crucial for the initiation of transcription
Without the Sigma polymerase cannot recognise the promoter initiation falls once transcription initiate and the RNA chain beings to elongate the Sigma subunitt is no longer needed
Dharmpal Swami
November 3, 2025Sigma subunit
Shivani
November 3, 2025The σ-subunit ensures that transcription begins at the right site by recognizing the promoter.
Kajal
November 4, 2025Correct Answer: (4) σ-subunit
Rishita
November 4, 2025Sigma unit ensure that transcription begins .
Deepika Sheoran
November 4, 2025Sigma subunit
Manisha choudhary
November 5, 2025Sigma factor
MOHIT AKHAND
November 9, 2025Done sir ✅
Neelam Sharma
November 13, 2025Sigma factor