Following ingestion of wild mushrooms collected during a trek, a 34-year-old man develops severe vomiting, watery diarrhoea, and later fulminant hepatic failure. The toxin responsible selectively inhibits which enzyme?

• A Eukaryotic RNA polymerase II ✓
• B Bacterial RNA polymerase
• C Eukaryotic RNA polymerase I
• D Eukaryotic peptidyl transferase

Explanation

Alpha-amanitin from Amanita phalloides is a potent and selective inhibitor of eukaryotic RNA polymerase II, blocking messenger RNA synthesis and causing hepatocyte death. RNA polymerase I is relatively resistant and polymerase III requires very high concentrations, so rRNA synthesis continues longer than mRNA synthesis. Bacterial RNA polymerase is unaffected, which distinguishes amanitin from rifampin, and peptidyl transferase is a ribosomal target unrelated to this toxin.

Reference: Lippincott's Illustrated Reviews: Biochemistry, 7th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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