FIGURE 4.
Restriction of Exo1 action by Ku at blunt and 5′-recessed DNA ends. A–D, DNA substrates (4 nm each) that had a blocked end and also a free blunt end (A) or a 7-nt (B), 22-nt (C), or 40-nt (D) 5′-recessed end were preincubated without (left panels) or with 5 (middle panels) or 20 nm (right panels) Ku for 10 min before adding Exo1 (0.25, 0.5, 1, and 2 nm), followed by a 5-min incubation. Quantification of the results is shown to the right. Error bars represent 1 S.D. based on results from three independent experiments, and asterisks denote the 32P label.