Inhibition of transcription by α-amanitin. (a) A mushroom to avoid! Amanita phalloides is poisonous to eukaryotes because it produces α-amanitin. (b) The chemical structure of α-amanitin. (c) Binding of α-amanitin (red) to yeast Pol II. (d) α-Amanitin inhibits synthesis of mRNA by Pol II, but not synthesis of rRNA by Pol I or tRNA by Pol III. The image shows a gel matrix in which RNA of a particular size is detected; in the presence of α-amanitin, RNA is made by Pol I and Pol III, but not by Pol II. (Note that pre-