A mushroom picker develops severe gastroenteritis followed by progressive hepatocellular failure after eating wild mushrooms. The toxin responsible selectively binds and inhibits one of the three eukaryotic RNA polymerases. Which enzyme is inhibited?

• A RNA polymerase II ✓
• B RNA polymerase I
• C RNA polymerase III
• D Mitochondrial RNA polymerase

Explanation

Alpha-amanitin from Amanita phalloides is a tight-binding inhibitor of RNA polymerase II, the enzyme that synthesises mRNA, causing transcription arrest and hepatocyte death at very low concentrations. RNA polymerase I is resistant, and polymerase III shows intermediate sensitivity only at much higher doses. This differential sensitivity is a classic exam fact linking a clinical poisoning to the enzyme responsible for messenger RNA synthesis.

Reference: Lippincott's Illustrated Reviews: Biochemistry, 8th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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