Figure 7. Effect of RECQ1 depletion on G2/M and intra-S-phase DNA damage checkpoints.

Panel A, DNA damage-induced mitotic entry delay is minimally affected by the RECQ1 deficiency. HeLa cells were transfected with the indicated siRNAs and either mock-treated or exposed to 3 Gy of IR 1 h before harvesting. Mitotic cells were detected by PI and phosphohistone H3 staining and analyzed by flow cytometry. Percentages of mitotic cells and their levels normalized to control (in parentheses) are shown. Panel B, RECQ1 is involved in maintenance of IR-induced G2/M checkpoint. Cells with either control or RECQ1 siRNA were exposed to 10 Gy of IR. Nocodazole (1 µg/ml) was added to the medium at the time of IR treatment to capture cells entering mitosis. 16 h later, cells were collected for PI and phospho-histone H3 staining and analyzed by flow cytometry. Panel C, HeLa cells transfected with control or RECQ1 siRNAs were exposed to 10 Gy of IR and assayed for DNA synthesis 30 min later by [³H]thymidine incorporation. The amount of DNA synthesis after irradiation is expressed as a percentage of the level in untreated cells. Error bars indicate SD from three independent experiments.