Question

The enzyme that displaces histone octamer during transcription is

• A. DNA polymerase
• B. Gyrases
• C. Helicases
• D. RNA polymerase

Hint:

RNA polymerase acts as the primary molecular engine during transcription.
It works alongside histone chaperones like FACT to displace histone octamers from nucleosomes, allowing transcription through chromatin templates.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
In eukaryotic cells, genomic DNA is packaged around histone octamers to form nucleosomes.
This compact chromatin structure blocks access to transcription factors and the transcriptional machinery, meaning nucleosomes must be temporarily disrupted to allow transcription to occur.

Step 2: Detailed Explanation:
During eukaryotic transcription elongation, the transcribing RNA polymerase complex must navigate through this nucleosomal DNA template.
As RNA polymerase moves along the gene, the mechanical force generated by the transcribing enzyme, along with histone chaperones (such as FACT) and chromatin remodeling complexes, temporarily displaces the histone octamers ahead of the transcription fork.
The histone octamer is disrupted, allowing RNA polymerase to transcribe the DNA template.
Once the polymerase passes, the chaperones help reassemble the histone octamers back onto the DNA behind the transcribing complex.
DNA polymerase (A) is responsible for DNA replication rather than gene transcription.
Gyrases (B) and helicases (C) function to relieve supercoiling and unwind the double helix, respectively, but they do not serve as the primary transcribing enzymes that displace histones during transcription.

Step 3: Final Answer:
Therefore, the enzyme that displaces the histone octamer during transcription is RNA polymerase, corresponding to option (D).