Final answer:
Alpha-amanitin in Amanita phalloides blocks transcription by inhibiting RNA polymerase II, providing clues to gene function based on polymerase sensitivity.
Step-by-step explanation:
The toxin alpha-amanitin found in the death cap mushroom, Amanita phalloides, is known to inhibit RNA polymerase, particularly RNA polymerase II, which is extremely sensitive to the toxin. This inhibition blocks the transcription of DNA into RNA, a critical process in gene expression. Inhibition of RNA polymerase III by alpha-amanitin is less severe, while RNA polymerase I is completely insensitive. The susceptibility of different RNA polymerases to alpha-amanitin provides researchers with a tool to determine which polymerase is responsible for transcribing a particular gene and thus gain insight into the gene's function. Given that RNA polymerase II transcribes the majority of genes, its inhibition by alpha-amanitin would result in significant disruption to cellular functions.