Figure 3. Impact of tail polarity on unwinding by DDX3X and Ded1p.

(a) Functional binding isotherms for DDX3X for 16 bp substrates with 25 nt unpaired tails 3′ (open circles) or 5′ (closed circles) to the duplex. The inset shows the isotherm for the 5′ tailed substrate with magnified y-axis. Data points represent averages of at least three independently measured unwinding rate constants, error bars mark one standard deviation. Lines show best fits to the Hill equation (3′ tailed substrate: K_1/2 = 112 ± 6 nM, k_unw^max = 4.2 ± 0.2 min⁻¹, H = 3.1 ± 0.6 ; 5′ tailed substrate: K_1/2 = 127 ± 20 nM, k_unw^max = 0.20 ± 0.02 min⁻¹, H = 3.2 ± 1.2.

(b) Functional binding isotherms for Ded1p for 16 bp substrates with 25 nt unpaired tails 3′ (open circles) or 5′ (closed circles) to the duplex. Data points represent averages of at least three independently measured unwinding rate constants, error bars mark one standard deviation.