ATPase activity of 5 µM eIF4A in the presence of saturating (5 mM) ATP•Mg2+ as a function of the concentration of capped RPL41A mRNA for (A) eIF4A (no PIC): kcat = 0.48 ± 0.04 min−1, = 80 nM; (B) Solid black circles: Complete PIC (contains 5 µM eIF4A, 0.5 µM eIF4G•4E, 0.5 µM eIF4B, 0.5 µM eIF2, 0.5 µM Met-tRNAi, 1 mM GDPNP•Mg2+, 0.5 µM eIF3, 0.5 µM eIF5, 1 µM eIF1, 1 µM eIF1A, and 0.5 µM 40S subunits): kcat = 9.0 ± 0.8 min−1, = 260 ± 40 nM. White circles: ‘Complete PIC-40S’ (contains all ‘Complete PIC’ components except the 40S subunit): kcat = 5.3 ± 0.1 min−1, = 270 ± 70 nM. Solid black squares: 4A•4G•4E alone (no PIC) (contains 5 µM eIF4A and 0.5 µM eIF4G•4E only): kcat = 3.2 ± 0.2 min−1, = 100 ± 10 nM. (C) kcat values for ATP hydrolysis from the experiments described in (A) and (B) plus additional drop-out experiments. In all cases, saturating (0.5 µM) capped RPL41A mRNA was present. The components present in the reactions, as indicated to the left of each bar, were at the same concentrations as in (B). (D) ATPase activity of 5 µM eIF4A alone or in the presence of a PIC missing eIF4G•4E as well as other components, as indicated to the left of each bar, all measured in the presence of saturating (0.5 µM) capped RPL41A mRNA. The concentrations of all components, when present, were the same as in (B). Note that the axis scales in panels (C) and (D) are the same for ease of comparison. All data presented in the figure are mean values (n ≥ 2) and error bars represent average deviation of the mean.