ε-Amanitin is a cyclic peptide obtained from various mushroom species. It exhibits a strong affinity for RNA polymerase II and effectively inhibits its activity.

Amatoxin Family includes alpha-Amanitin, beta-Amanitin, gamma-Amanitin, epsilon-Amanitin (ε-Amanitin), Amanullin, Amanullinic acid, Amaninamide, Amanin and Proamanullin. Amatoxins are potent and selective inhibitors of RNA polymerase II, a vital enzyme in the synthesis of messenger RNA (mRNA), microRNA, and small nuclear RNA (snRNA). By inhibiting the synthesis of mRNA, Amatoxins thereby stop cell metabolism by inhibiting transcription and protein biosynthesis, which results in cellular apoptosis. Consequently Amatoxins stop cell growth and proliferation[1].