Figure 4.

Pre-steady-state kinetics of translocation in the presence of phosphate analogues at pH 6.0. mRNA translocation was induced by mixing pretranslocation ribosomes (35 nM after mixing) EF-G (1 µM after mixing) preincubated with GTP (blue), GDP (dark green), GDP and BeF₃⁻ (red) or GDP and AlF₄⁻ (magenta). Pretranslocation ribosomes were also mixed with buffer only (cyan) to account for the rates of the photobleaching of fluorescein and spontaneous translocation. Experiments were performed in polyamine buffer at pH 6.0. Double-exponential fits for fluorescence quenching (black lines) are reported in Table 1. Same kinetic traces are shown in the two time scales set to 5 s (panel a) and 250 s (panel b).