Fig. 4. Cru1 is required for adaptation to nitrogen starvation. (A) The cru1 cells cannot arrest in the G1 phase upon nitrogen starvation. Wild-type and mutant strains growing in nutrient-rich medium until mid-exponential phase were transferred to minimal medium without nitrogen (MM-N) for the duration indicated and analyzed by flow cytometry. (B) DAPI staining of wild-type and mutant cells after 8 hours incubation in nitrogen starvation conditions. Notice the presence of a single nucleus per cell. Bars, 10 µm. (C) Survival of wild-type and mutant cells in medium lacking nitrogen after 3 days. Cells were grown in nutrient-rich medium to around 10⁶ cells/ml, washed, resuspended in MM-N and incubated at 28°C. Aliquots of each culture were extracted at the indicated times and cells were counted on YPD plates to determine the number of viable cells.