FIGURE 4.

WRN degradation of telomeric ssDNA is inhibited by RPA and POT1 loading. A, schematic of WRN exonuclease activity on the 120-nt ssDNA strand after release from the D-loop. The thick line represents the (TTAGGG)₁₀ repeats, and the asterisk denotes the radiolabel. Circles with solid lines represent either RPA or POT1 binding, and circles with dashed lines represent only RPA binding. B, reactions contained 50 pm free telomeric ssDNA. The substrate was incubated with 5 nm WRN alone (lane 2) or with increasing concentrations (2.5, 7.5, 20, or 60 nm) of either POT1 (lanes 3–6) or RPA (lanes 8–11) for 15 min under standard reaction conditions. Control reactions contained substrate with either 60 nm POT1 (lane 7) or RPA (lane 12). Reactions were run on 14% polyacrylamide denaturing gels and visualized by PhosphorImager analysis.