FIG. 4.

Dap1p regulates cell cycle progression following DNA damage. (A and B) Unsynchronized wild-type (A) or dap1Δ (B) cells were treated with 0.05% MMS and then fixed and counted at the time points indicated. Cells were scored microscopically as unbudded (left bars), small budded (center bars), or doublets (right bars). In dap1Δ cells, there was a twofold increase in the number of unbudded cells and a sixfold increase in the percentage of large-budded cells within 2 h of MMS addition. The strains analyzed were RCY409-2a (wild type) and RCY409-4b (dap1Δ). (C) The budding profiles of four different strains were compared at 2 h following the addition of 0.05% MMS. The strains were RCY409-2a (wild type), RCY409-4b (dap1), RCY406-1d (rad9), and RCY406-5a (dap1 rad9). Deletion of the RAD9 gene did not reverse the G₁ arrest observed in dap1 mutants following MMS-induced damage. Error bars indicate standard deviations.