Figure 4.

(A) Wild-type (wt), rad3-d, cds1-d, and chk1-d cells were grown to mid-log phase and irradiated with either 250 or 500 Gy of ionizing radiation. After 45-min recovery, protein was extracted. Total protein (pellet fraction; 50 μg) was analyzed by Western blotting with 9E10. (B) FACS profiles of elutriation-synchronized rad3-d and chk1-d cells after irradiation (250 Gy between −20 and 0 min) during G₁/S. Both strains are defective for the G₂/M checkpoint and do not arrest mitosis when irradiated. The major difference between rad3-d and chk1-d is the lack of a Cds1 response. S phase is delayed by irradiation in chk1-d (cds1⁺) cells but not in rad3-d.