DNA binding of Ku mutants under reduced conditions as assessed by EMSA. (A) C493A point mutant and wild type Ku were assessed for binding to a duplex 30-bp DNA substrate as described in "Methods". Reaction products were separated via native electrophoresis and visualized via PhosphorImager. (B) Ku70/80ΔC and wild type Ku (0-150 nM) were subject to the same analysis. (C) Quantification of the results in Panel B was performed via PhosphoImager analysis. Results are presented as the average and standard deviation of triplicate determinations and binding curves were fit. Filled circles represent wild type Ku, open circles represent Ku70/80ΔC.