SecYEG forms a quaternary complex with RNC, SRP, and FtsY. (A) Kinetics of the closed complex assembly were measured in the absence (red) and presence of 100 nM RNC (green), and in the presence of 100 nM RNC and 7 µM SecYEG (blue). Reactions contained 40 nM DACM-labeled SRP, 100 nM BODIPY-FL–labeled FtsY, and 200 µM GppNHp. (B) Kinetics of the early → closed rearrangement of the RNC–SRP–FtsY complex in the absence (black) and presence (red) of 12 µM SecYEG. The data were fit to Eq. 2. Single exponential fits to the data gave rearrangement rate constants of 0.403 ± 0.027 and 0.489 ± 0.008 s⁻¹ with and without SecYEG, respectively. (C) Summary of the early → closed rearrangement rate constants. The value of 1.5 s⁻¹ was obtained in the absence of SecYEG and RNC. A and B show representative data from three replicates. Error bars indicate average ± SD.