Figure 1.

 Checkpoint and survival analysis of cds1 mutants. All designations indicate null alleles, with the exception of r26.T12, which designates the rad26.T12 allele. (A) cds1 null mutant cells display mitotic arrest following inhibition of S phase with HU. Synchronous cultures of G₂ cells were generated on lactose gradients (Barbet and Carr 1993) and divided into two samples, one of which was incubated in 10 mm HU. Septation index and DAPI staining were used to follow progress through the cell cycle. cds1 mutants arrested mitosis for over 6 hr following S-phase arrest. In contrast, a representative of the checkpoint rad group of mutants, rad3, entered mitosis without completing S phase. (B,C) Radiation survival of logarithmically growing cells show that cds1 null mutant cells are sensitive to damaging agents and show increased sensitivity with chk1, but not rad26.T12. (D) cds1 cells, in contrast to checkpoint-defective (rad26) cells have a normal DNA-damage checkpoint at mitosis. Synchronous cultures of G₂ cells were generated on lactose gradients and dividend into four samples. One sample was not irradiated, whereas one each was irradiated with 50, 250, or 500 Gy of ionizing radiation.