14. Actinomycin D inhibits the process of transcription in both prokaryotic and eukaryotic organisms. The following statements are made about actinomycin D-mediated inhibition of transcription:
(1) Actinomycin D inhibits transcription from a double stranded DNA template by either E. coil or yeast RNA polymerases.
(2) Actinomycin D inhibits transcription from a single stranded RNA template by eukaryotic viral RNA
(3) Actinomycin D inhibits transcription from single stranded Φ x 174 DNA template by E. coli RNA polymerase, immediately after viral DNA entry.
(4) Actinomycin D inhibits transcription from double stranded RNA template by eukaryotic RNA polymerase II.

Which of the combinations of the above statements is a true representation mediated inhibition  of the mechanism of actinomycin D
(1) A only                   (2) A, B and D
(3) A, B and C            (4) A and D only

Detailed Explanation:

Actinomycin D is a well-known transcription inhibitor that works in both prokaryotes and eukaryotes by intercalating into double-stranded DNA and blocking RNA polymerase movement.

How Actinomycin D Works:

• Intercalates between adjacent G-C base pairs in double-stranded DNA.

• Prevents the unwinding of DNA necessary for RNA polymerase progression.

• Inhibits DNA-dependent RNA synthesis, not RNA-dependent RNA synthesis or reverse transcription.

Let’s analyze each statement:

(1) Actinomycin D inhibits transcription from a double-stranded DNA template by either E. coli or yeast RNA polymerases.

• True

• This is the primary mechanism of Actinomycin D action.

• Works in both prokaryotic and eukaryotic RNA polymerases on dsDNA.

(2) Actinomycin D inhibits transcription from a single-stranded RNA template by eukaryotic viral RNA.

• False

• Actinomycin D does not affect RNA-dependent RNA polymerases.

• It does not act on RNA templates, only on double-stranded DNA.

(3) Actinomycin D inhibits transcription from single-stranded ΦX174 DNA template by E. coli RNA polymerase, immediately after viral DNA entry.

• False

• ΦX174 is a single-stranded DNA virus.

• Actinomycin D requires double-stranded DNA to intercalate.

• It does not bind or inhibit transcription from ssDNA templates.

(4) Actinomycin D inhibits transcription from double-stranded RNA template by eukaryotic RNA polymerase II.

• False

• RNA polymerase II only transcribes DNA to RNA, not dsRNA.

• Additionally, actinomycin D doesn’t bind RNA—only DNA.

 Summary Table:

 Final Answer: (1) A only