Figure 3: Assays to determine the ability of EF-Ts to stimulate GDPexchange by EF-Tu were as described under Section 2. The concentration of EF-Tu was held at 0.64 μM. EF-Ts concentrations were 0.05 μM (1 : 13 EF-Ts to EF-Tu ratio) when present, and the reaction times for the assays ranged from 15 to 120 s. Activity is the amount of [3H]GDP (1500 cpm/pmol) bound by EF-Tu. EF-Tu exchange activity in the presence (●) and absence (■) of EF-Ts.