FIG. 4.

S-phase defects of SL2 cells depleted of dE2F1, dE2F2, or dDP. (A and B) Cells depleted of dE2F1, dE2F2, and dDP were labeled with [³H]thymidine to measure DNA synthesis or with BrdU for 16 h and subjected to two-dimensional FACS analysis. The error bars indicate standard deviations. (C) Proliferation indices of cells following RNAi treatment. Loss of dE2F1 results in a significant reduction of S-phase cells and an increased G₁ population. Removal of dE2F2 restores S-phase entry defects of dE2F1-depleted cells but does not rescue S-phase progression defects. Despite containing BrdU-positive cells, populations of dDP, dE2F1/dE2F2, dE2F1/dDP, and dE2F1/dE2F2/dDP RNAi-treated cells have low rates of DNA synthesis and proliferate very slowly. In populations of dDP- or dE2F1/dE2F2-depleted cells, a substantial number of BrdU-negative cells have intermediate DNA contents, indicating that these cells are stalled within S phase.