FIG. 2.

DDB1 depletion results in γH2AX, Mre11, and RPA focus formation. U2OS cells were transfected with control or DDB1 siRNA oligonucleotides. Cells transfected with control siRNA were also irradiated with 8 Gy of IR 2 hours prior to analysis where indicated. (A) Three days after siRNA transfection the cells were fixed and stained with antibodies to H2AX phospho-S139 and Mre11, followed by the appropriate FITC and rhodamine red-X secondary antibodies. The nucleus was visualized with DAPI. (B) The percentage of U2OS cells displaying five or more intranuclear γH2AX foci 3 days after transfection with control or DDB1 siRNA oligonucleotides was quantified. (C) The number of γH2AX foci per cell was quantitated. (D) Cells were fixed and stained with an antibody to RPA34. DAPI staining was used to visualize the nucleus.