DMSR only occurs in G0 or G1 cells. (A) The experimental procedure for DMSR analysis in serum-starved G0 cells is shown. The U2OS cell cycle stage in indicated time points was determined by flow cytometry (related to Fig. 3, A and B). (B) U2OS cells were synchronized at G1/S and released for indicated time points. Cells were then treated with 2 Gy IR, and DMSR was determined at 2 h after IR treatment by microtubule regrowth assay. The detailed procedures and U2OS cell cycle stage at each time points are shown. Cell cycle stage was determined by flow cytometry. Upper: G1/S phase cell. Middle: G1/S released 3 h. Lower: G1/S-released 5 h. PI, propidium iodide.