FIGURE 4.

Polymerase β extension activity in free and nucleosomal DNA. A, intact or gap-containing free DNA and NCPs were incubated with pol β (200 nm), indicated by +, for 30 min at 37 °C. Lane M corresponds to the radiolabeled 10-bp DNA ladder. Lanes 1 and 6 correspond to intact DNA-UO (+10) and NCP-UO (+10) respectively. pol β extension was quantified as the appearance of slower migrating bands relative to the untreated (− pol β) lane. The percent extended was calculated as described under “Experimental Procedures.” B, NCPs incubated with increasing amounts of pol β (50, 200, and 500 nm) at 37 °C for 30 min.