FIGURE 5.

Effect of a 5′-cap and ssRNA sequence on RNA unwinding by eIF4F. The RNA unwinding activity of wild-type eIF4F was measured with different dsRNA substrates (Table 1). A, eIF4F-catalyzed unwinding of 5′-30-nt-ds10 substrate (Table 1) with (▴) or without (●) a 5′-⁷mG cap. B, comparison of eIF4F-catalyzed unwinding of a 10-bp duplex with two different 30-nt 3′-overhangs. The kinetics of unwinding are the same with the standard 3′-overhang (3′-30-nt-ds10; Table 1 (▴)) and one that is identical to the 30-nt single-stranded region of the 5′-overhang dsRNA substrate (3′-5 seq-30 nt-ds 10; Table 1 (●)). C, eIF4F-catalyzed unwinding of a 10-bp duplex substrate with a 15-nt 5′-overhang (▾) and a 15-nt 3′-overhang (●) (Table 1). D, dependence of eIF4F unwinding rate upon lengths of 3′- or 5′-overhangs. The unwinding rate of a 10-bp duplex with a 50-nt 3′-overhang was not measured. Conditions were the same as in Fig. 3.