Final answer:
α-amanitin from the Death Cap mushroom inhibits RNA polymerase II, impacting RNA synthesis and is used to study gene function.
Step-by-step explanation:
α-amanitin is a toxic compound found in the Death Cap mushroom (Amanita phalloides) and is known for its potent inhibition of RNA polymerase II in animals, leading to a halt in RNA synthesis. This particular mushroom toxin affects the three main RNA polymerases to varying degrees, with RNA polymerase I being completely insensitive to it, RNA polymerase III being moderately sensitive, and RNA polymerase II being extremely sensitive. This sensitivity of RNA polymerase II to α-amanitin is exploited by scientists to determine which polymerase transcribes a particular gene, thus aiding in the study of gene function.