Time-dependence of DSB rejoining in PARP-1+/+ and PARP-1-/- 3T3s following exposure to 30 nM NCS. [2-14C]Thymidine-labeled cells were exposed to NCS for 10-min. After drug removal, cells were rapidly chilled in ice at the time indicated, harvested, and embedded into agarose plugs followed by lysis and PFGE (see Methods). The results are expressed as the percentage of remaining damage in Gy.eq. This percentage was determined from the fraction of activity released from the plugs; calibration was made with reference to samples irradiated in ice. The origin of the time scale starts from the introduction of NCS.