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Eduncle posted an MCQ
December 30, 2019 • 15:40 pm 0 points
  • CSIR NET
  • Life Sciences

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 :
    (A)    Actinomycin D inhibits transcription from a double stranded DNA template by either E coli or yeast RNA polymerases.
    (B)    Actinomycin D inhibits transcription from a single stranded RNA template by eukaryotic viral RNA polymerases.
    (C)    Actinomycin D inhibits transcription from single stranded fx174 DNa template by E coli RNA polymerase immediately after viral DNA entry.
    (D)    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 of the mechanism of actinomycin D mediated inhibition.

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    Eduncle Best Answer

    Actinomycin D is an intercalating compounds with sequence selectivity. The actinomycin chromophore favours guanine-cytosine pairs and is therefore inserted between the G-C step. Hydrogen bonds are established between the guanine 2-amino group and the carbonyl oxygen of threonine, and also between the guanine N-3 atom and the NH group of the same threonine residue, helping to stabilize the actinomycin–DNA complex. The formation of this very stable actinomycin–DNA complex prevents the unwinding of the double helix which leads to inhibition of the DNA-dependent RNA polymerase activity and hence transcription.

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