FIG. 2.

Cells deficient in Yng2 display a persistent Mec1-mediated intra-S-phase delay. To examine the intra-S-phase checkpoint, the wild type (YNG2) and yng2 and yng2 mec1 mutants were arrested in G₁ with αf, treated with 0.03% MMS for 45 min, and then released into the presence of 0.03% MMS at 22°C. Cells were collected at the indicated times and processed for flow cytometry using propidium iodide. 1N indicates haploid DNA content, and 2N indicates replicated DNA. YNG2 cells (A) display the characteristic slowed S phase in the presence of MMS, while yng2 single mutants (B) arrest in S phase. In contrast, yng2 mec1 double mutants (C) progress through and complete S phase. As a control, cells which were not treated with MMS are shown (No MMS).