Fig. 8. Stimulation of ROS production and PI staining by HU requires abrogation of both the Cds1p- and Chk1p-dependent checkpoint pathways or dysregulation of Cdc2p. The indicated strains were incubated at 25°C for 4 hours with (+) or without (-) 12 mM HU. Then DCDHFDA was added, and incubation was continued for 80 minutes. The cells were stained with PI and analyzed by flow cytometry.