Fig. 8. Identification of a DNA damage checkpoint in Dictyostelium. (A) Cells were treated with bleomycin for 3 hours as indicated. The number of cell divisions occurring per hour was scored in mock-treated cells and those treated with 5 mU/ml or 20 mU/ml bleomycin. (B) After removal of bleomycin, cells escape the checkpoint and divide with increased synchronicity, as shown pictorially in these stills from a movie. Arrows indicate dividing cells.