Figure 4. WRN loops 5′ ssDNA periodically.

(a) Typical time traces of fluorescence intensities of Cy3 and Cy5 and FRET obtained with (dT)₄₀. Δt is defined as the time between two successive FRET peaks. (b) Histograms of Δt at different ATP concentrations were best fitted by a γ-distribution with time constant Δτ = 1.12, 1.31 and 1.42 s for 1 mM (27 traces), 100 μM (30 traces) and 75 μM ATP (20 traces), respectively. (c) Representative time traces of FRET showing repetitive looping of 5′-ssDNA tails with different lengths. (d) Time constant Δτ versus 5′-tail length at 1 mM ATP. A WRN translocation rate of 30 ± 6 nt/s was obtained by a linear fit of the data (Error bar = s.e.m.).