Persistent G1 cell cycle arrest in hog1Δ cells during continuous exposure to arsenite. (A) The results of flow cytometry reveal accumulation of G1 cells in asynchronously growing hog1Δ cells in the presence of 0.5 mM arsenite. (B) G1-synchronized hog1Δ cells fail to restart the cell cycle under permanent arsenite stress. (C) The α-factor-nocodazole trap assay results confirm persistent G1 arrest of hog1Δ cells. (D) Duration of G2/M checkpoint delay in hog1Δ cells is not affected during arsenite exposure. (E) Lack of Hog1 kinase activity results in a persistent G1 arrest, similar to that of hog1Δ cells. Cells with the analogue-sensitive HOG1-as allele were synchronized in G1 with α-factor, exposed to 12 μM of the inhibitor 1-NM-PP1 for 5 min, washed in the presence of inhibitor, and released in fresh medium containing 12 μM 1-NM-PP1 in the presence or absence of 0.25 mM arsenite. In a control experiment, no inhibitor was added. At 10-min or 20-min intervals, samples were collected for the α-factor-nocodazole trap assay. As(III), arsenite; +, present; −, absent; 1C and 2C, values of DNA content; WT, wild type.