Analysis of episomes during a time course of recovery from IR. 2 × 107 cells transformed with BK-Shuttle or TLK1B were irradiated (or not, C) with 20 Gy of γ-radiation. The cells were returned to the incubator and the plasmids were isolated immediately after radiation (IR), or after the indicated times of recovery, 2 to 8 hr (R2-R8). The episomes were recovered by alkaline lysis, which removes plasmids with DSBs by strand separation followed by the rapid renaturation. This is because it is not always easy to separate on agarose gels the linearized from the supercoiled form of the plasmid (these plasmids are 11–14 kb in size, without and with insert). The bands were quantified with ImageQuant. The intensities of the bands relative to control are indicated underneath each lane. Size markers (Novagen 1 kb ladder) are shown in the first lane.