FIGURE 1.

DNA Pol δ can degrade DNA with alternate structures. Increasing amounts of human 4-subunit Pol δ holoenzyme were incubated with 10 nm concentrations of either blunt duplex DNA, a blunt duplex with an internal 8-nt bubble, a model X-junction structure, or a D-loop mimic as described under “Experimental Procedures” (30, 100, and 300 fmol of Pol δ with all substrates, except D-loop that was incubated with 18, 60, and 180 fmol of Pol δ). The reactions were incubated at 37 °C for 20 min (10 min with D-loop DNA), terminated by the addition of formamide stop solution, boiled, and aliquots were electrophoresed through 14% urea polyacrylamide gels. The gels were dried, imaged, and quantified on a PhosphorImager (GE Healthcare).