Alpha-amanitin, a specific inhibitor of transcription by mammalian RNA-polymerase.

Evidence has been presented that a amanitin, the potent bicyclic polypeptide toxin of the toad­ stool amanita phalloides inhibits transcription by purified RNA polymerase from rat liver nuclei. This inhibition is highly specific for the mammalian enzyme, since it does not impede the same reaction catalyzed by the enzyme from E. coli thus rendering an interaction between the template and inhibitor very unlikely, a Amantitin is a very potent inhibitor and calculations show an ap­ proximate stoichiometry of 1 : 1 between enzyme and inhibitor. In addition, evidence is formarded suggesting that the inhibitor allows chain initiation to occur, but abruptly inhibits elongation of RNA chains.