Fig. 3.

Force-velocity curves. Average pause-free elongation rates (errors as SEM) measured as functions of force for (A) WT, (B) E1103G, and (C) H1085A/E1103G RNAPII at saturating (1 mM) and subsaturating (0.1 mM) NTPs, as well as in the presence of 100 mM ammonium chloride, which was added to our standard elongation buffer. Global fits to the two-binding site Brownian ratchet model (Model 3, Fig. 2C) are shown (dashed lines).