FIGURE 3.

Engagement of 5′-recessed DNA ends by Ku. A–E, Ku (1.25, 2.5, 5, 10, and 20 nm) was incubated with DNA substrate (4 nm each) with one of its ends blocked by a biotin-streptavidin complex and also with a free blunt end (A) or a 7-nt (B), 22-nt (C), 40-nt (D), or oligo(dT)₄₀ (40T or dT40; E) 5′-recessed end for 10 min. F, quantification of the results in A–E. G, Ku (5 nm) was incubated with the substrate containing a 40-nt 5′-recessed end (4 nm) for 10 min, and unlabeled 40-bp blunt-ended dsDNA (0, 2, 4, 8, and 16 nm) was added, followed by a 10-min incubation. Quantification of the results is shown to the right. In A–E and G, PK lanes represent a reaction was treated with SDS and proteinase K prior to analysis, and asterisks denote the ³²P label. Error bars in F and H represent 1 S.D. based on results from three independent experiments.