Figure 1.

WRN does not increase primer extension by DNA polymerase α or ɛ. A 5′-end labeled 14-nt DNA primer was hybridized to a 46-nt DNA template. The primer (0.1 pmol) was extended by DNA polymerase α or ɛ in the absence or presence of increasing concentrations of WRN (1.2–60 fmol). The reactions were incubated at 37°C for 10 min and were terminated by the addition of an equal volume of denaturing loading buffer. Aliquots were electrophoresed through 14% polyacrylamide-urea gels, and extension products were visualized by autoradiography. The panel labeled “(−) Pol” is a control of increasing concentrations of WRN incubated with the primer/template in the absence of DNA polymerase to demonstrate the products of the 3′→5′ exonucleolytic activity of WRN.