FIG. 3.

(A) Effect of WSC1 and MID2 inactivation on expression of the PST1-lacZ reporter gene during low-pH stress. Cells transformed with YEp357R-PST1 were grown in YNB medium to an OD₆₀₀ of 0.5. The pH was decreased from 3.5 to 2.8 at time zero (indicated by an arrow). β-Galactosidase activity was followed during 6 hours after the shock in wild-type (▪), wsc1Δ (▴), and mid2Δ (•) strains. (B) Effect of WSC1 and MID2 inactivation on expression of the ADE1-lacZ reporter gene during low-pH stress. Cells were transformed with the YEp357R-ADE1 plasmid. The experimental conditions and symbols are the sameas described above (A). (C) Effect of RGD1 and MID2 inactivation on low-pH tolerance. Cells of wild-type, rgd1Δ, mid2Δ, and rgd1Δ mid2Δ strains and 10-fold serial dilutions thereof were spotted onto YPD and YPD medium adjusted at pH 3.0 by adding hydrochloric acid and incubated for 3 days at 30°C. (D) Suppression of rgd1Δ and rgd1Δ mid2Δ sensitivity to low pH by WSC1 and MID2 overexpression. The viability of indicated mutants as well as the viability of the rgd1Δ and rgd1Δ mid2Δ strains transformed with YEP352 WSC1-3HA, YEP352 MID2-3HA, or control vector were determined after low-pH stress. Cells were grown in YNB medium to an OD₆₀₀ of about 0.5, and the pH was decreased from 3.6 to 2.8. Viability was measured after 6 h. Data concerning the effect of WSC1 and MID2 overexpression were averages from results obtained from three independent transformants. WT, wild type.