Question

The inhibition of RNA synthesis in prokaryotes by the action of Actinomycin D emphasis the importance of which of following process?

• A. Recoganition of promotor sequence
• B. Formation of template strand
• C. Detection of terminator signal
• D. Annealing of primer

Hint:

Actinomycin D intercalates into DNA, thereby blocking the replication and transcription machinery from using the DNA as a template.
It is widely used in laboratory research to study the half-life of existing mRNA molecules.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Actinomycin D is a polypeptide antibiotic isolated from Streptomyces species.
It is a well-known transcription inhibitor in both prokaryotes and eukaryotes.
Detailed Explanation:
- Actinomycin D functions by intercalating its phenoxazone ring system specifically between adjacent Guanine-Cytosine (G-C) base pairs in double-stranded DNA.
- Once intercalated, the peptide chains of the drug extend into the minor groove of the DNA double helix, stabilizing the complex.
- This binding prevents the DNA from unwinding and acting as a template for RNA polymerase.
- By blocking the movement of RNA polymerase along the DNA, it halts transcription elongation.
- This inhibition demonstrates that the physical accessibility and structural integrity of the double-stranded DNA template (acting as the template strand) is an absolute prerequisite for transcription.
- It does not prevent promoter recognition directly or block primer annealing (as no primers are used in de novo transcription).

Step 2: Final Answer:
The inhibition highlights the critical requirement of the formation and availability of the template strand, corresponding to option (B).