From the crystal structure solved by Dr. Bushnell et al.,[18] α-Amanitin interacts with the bridge helix in RNA polymerase II (pol II). This interaction interferes with the translocation of RNA and DNA needed to empty the site for the next round of RNA synthesis. The addition of α-amanitin can reduce the rate of pol II translocating on DNA from several thousand to a few nucleotides per minute,[19][20] but has little effect on the affinity of pol II for nucleoside triphosphate,[21] and a phosphodiester bond can still be formed.[22][23] The bridge helix has evolved to be flexible and its movement is required for translocation of the polymerase along the DNA backbone.