FIGURE 4.

The ability of neomycin to stimulate spontaneous reverse translocation depends on the h44 site. Reverse translocation in control (A), A1408G (B), or G1491U (C) ribosomes was measured in the absence and presence of Neo (as indicated). The fraction of ribosomes in the POST state was plotted versus time, and the data were fit to a single exponential function to obtain the observed rate at 0, 0.5, and 3 µM Neo (respectively): Control, k_obs = 0.16, 0.54, 0.60 min⁻¹; A1408G, k_obs = 0.15, 0.15, 0.15 min⁻¹; G1491U, k_obs = 0.15, 0.14, 0.20 min⁻¹.