Fig. 5. Phosphorylation of Grp/DChk1 in response to HU or IR is dependent on the expression of Mei-41/DATR. Western-blot analysis of Grp/DChk1 in control S2 cells and in Mei-41/DATR-depleted S2 cells treated with 10 mM HU during 15 hours or treated with 150 Gy IR followed by 2 hours of recovery. Compared with untreated cells (lanes 1,3,5,7), phosphorylated Grp/DChk1 was detected as a slower-migrating protein in control S2 cells treated with HU (lane 2) or IR (lane 4) and in Mei-41/ATR-depleted S2 cells treated with HU (lane 6) or IR (lane 8), no phosphorylation of Grp/DChk1 was observed. As a loading control, CP190 protein levels were detected.