FIGURE 8.

Proline protects hog1 and ire1 null mutants against ER stress. A and B, spot assays of yeast WT, ire1, and hog1 cells containing an empty vector (V) or the vector expressing the PRO1 mutant (PRO1-D154N) on SD plates alone (SD) or with DTT and Tm. C, cell death rate of hog1 cells assayed by PI staining. Mutant cells were grown in SD medium to log phase and were then treated with 2 mm DTT or 1 μg/ml Tm in the presence of varying concentrations of proline (0, 10, and 20 mm) for 16 h. Dead cells were then stained with PI. D, KAR2 mRNA levels were analyzed by real-time PCR in WT and hog1 cells grown in SD medium to log phase without (−Pro) or with (+Pro) 20 mm proline followed by treatment with Tm (1 μg/ml) for 0, 2, and 4 h. The mRNA levels were normalized to the internal control ACT1 with the lowest expression set at 1 (*, p < 0.05). Data are the mean ± S.D. from three independent experiments.