Distribution of foci numbers per nucleus. Synchronized normal human diploid cells in G1 were electroporated with 100 U of Pst I and Sph I with or without 20 μM KU55933. The cells were incubated for 24 or 48 hours after the treatment, and the foci numbers in Type III nuclei were counted. At least 500 nuclei were examined. Black bars: cells treated with KU55933. White bars: cells treated without KU55933.