A man who ingested wild mushrooms develops severe gastrointestinal symptoms followed by progressive hepatocellular failure. The toxin responsible selectively inhibits which enzyme?
- A Bacterial RNA polymerase holoenzyme
- B Eukaryotic RNA polymerase I
- C Eukaryotic RNA polymerase II ✓
- D Eukaryotic DNA polymerase alpha
Correct answer: C. Eukaryotic RNA polymerase II
Explanation
Alpha-amanitin from Amanita phalloides binds tightly to eukaryotic RNA polymerase II, blocking mRNA synthesis and causing hepatocyte death. RNA polymerase I is relatively resistant and polymerase III shows intermediate sensitivity, so rRNA and tRNA synthesis persist longer than mRNA synthesis. Bacterial RNA polymerase is unaffected, which distinguishes amanitin from rifampin. Inhibition of mRNA production explains why the liver, an organ of high biosynthetic turnover, fails first.
Reference: Harper's Illustrated Biochemistry, 32nd ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.