3. Which of the following compound is capable to inhibit transcription elongation, both in prokaryotes and eukaryotes?
(1) Rifamycin               (2) a-amanitin
(3) Streptomycin           (4) Actinomycin-D

Correct Answer

(4) Actinomycin D

Detailed Explanation

Actinomycin D is a well-known antibiotic and anticancer agent that inhibits transcription elongation in both prokaryotic and eukaryotic cells. It works by intercalating into DNA, particularly at GC-rich regions, and physically blocks the progression of RNA polymerase along the DNA template. This action halts the elongation phase of transcription, preventing the synthesis of new RNA molecules in all types of cells

Why Not the Other Options?

• Rifamycin: Specifically inhibits bacterial (prokaryotic) RNA polymerase during the initiation phase, not elongation, and has no effect on eukaryotic RNA polymerases.

• α-Amanitin: Selectively inhibits eukaryotic RNA polymerase II (and to a lesser extent, III), but does not affect prokaryotic transcription.

• Streptomycin: Inhibits protein synthesis by binding to the bacterial ribosome, not by affecting transcription.

Key Points about Actinomycin D

• Mechanism: Intercalates into DNA and blocks RNA polymerase movement, thereby inhibiting transcription elongation.

• Spectrum: Effective against both prokaryotic and eukaryotic RNA polymerases.

• Applications: Widely used in research to study gene expression and in chemotherapy for certain cancers.

Conclusion

Actinomycin D is the only compound among the options that inhibits transcription elongation in both prokaryotes and eukaryotes, making it a powerful tool in molecular biology and medicine.