FIGURE 6.

Ku binding to linear plasmid DNA. Reaction mixtures (20 μl) containing 50 mm Tris-HCl (pH 7.5), 5 mm DTT, 2% glycerol, 0.25 μg of SmaI-digested pUC19 DNA (∼145 fmol of plasmid; 290 fmol of double strand breaks), and 0.25, 0.5, or 1 μg of full-length Ku or KuΔ mutants as specified were incubated at 22 °C for 20 min. Ku was omitted from the control reactions shown in lane −. The mixtures were analyzed by electrophoresis through a horizontal 1% agarose gel in TBE. The gel was then stained with 0.05% ethidium bromide and photographed under UV illumination. The positions and sizes (kbp) of linear duplex DNA markers are indicated on the left.