Question

Which of the following is not related to termination of a transcript in E. coli?

• A. Intrinsic terminators
• B. Rho protein
• C. N protein
• D. NusA

Hint:

Remember that bacteriophage lambda N protein is a well-known antiterminator. It functions to prevent transcription termination, allowing the RNA polymerase to read through termination signals.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Transcription termination in *Escherichia coli* is the process by which the RNA polymerase enzyme stops transcribing DNA and releases the newly synthesized RNA transcript.
This occurs via two native mechanisms: Rho-independent (intrinsic) termination and Rho-dependent termination.

Step 2: Detailed Explanation:
Let us analyze the role of each option in transcription termination:
- Intrinsic terminators (A): These are native DNA sequences containing a G-C rich dyad symmetry followed by an A-T rich region.
They form a hairpin loop in the newly synthesized RNA, causing physical stalling and release of the transcript (Rho-independent termination).
- Rho protein (B): This is an ATP-dependent helicase that binds to the rut (rho utilization) site on the growing RNA transcript.
It moves along the RNA, catches up to the paused RNA polymerase, and unwinds the RNA-DNA hybrid to terminate transcription.
- NusA (D): This is a bacterial transcription elongation factor that binds to RNA polymerase.
It assists in the formation of the hairpin loop at intrinsic termination sites, enhancing termination efficiency.
- N protein (C): This is an antitermination protein encoded by bacteriophage lambda.
During viral infection, the N protein binds to the host RNA polymerase and prevents it from terminating at standard termination sites, allowing transcription of downstream viral genes.
Since the N protein is an *antiterminator* of viral origin rather than a native factor promoting host transcript termination, it is not related to the termination of a transcript in *E. coli*.

Step 3: Final Answer:
The N protein is not related to the termination of a transcript in *E. coli*.