Phosphodiester bond addition cycle of S.
cerevisiae RNAP II. Bridge helix is pink, trigger
loop is green, NTP substrate
is orange, RNA is purple, template DNA strand is blue, and nontemplate
DNA strand is silver. The image is adapted from PDB files 2E2H (closed trigger
loop) and 2E2J (open trigger loop). Reprinted with permission from ref (7a): Feig M.; Burton Z. F.. RNA polymerase II with open and closed trigger loops: Active site
dynamics and nucleic acid translocation. Biophysical
Journal 2010, 99(8), 2577.. Copyright 2010 Elsevier.