Figure 7.

Oxidative stress but not osmostress can induce ctt1⁺ expression independently of Spc1 activation. (A) Wild-type (KS2096) and wis1DD (KS2088) strains carrying the spc1:HA6H allele were grown to midlog phase at 30°C in YES medium and treated with either high-osmolarity stress induced by 0.6 M KCl (Os) or oxidative stress induced by 0.3 mM H₂O₂ (Ox). Aliquots of cells were harvested at the indicated times, and Spc1 was purified by Ni-NTA chromatography, followed by immunoblotting with anti-phospho-p38 and anti-HA antibodies. The level of active Spc1 does not change in wis1DD cells even after osmostress and oxidative stress. (B and C) Wild-type (PR109), wis1DD (KS2081), and Δwis1 (JM544) cells were grown to midlog phase in YES medium and treated with oxidative stress induced by 0.3 mM H₂O₂ (B) and high-osmolarity stress induced by 0.6 M KCl (C). Aliquots of cells were harvested at the indicated times for Northern hybridization analysis with the ctt1⁺ and leu1⁺ probes. In wis1DD cells, ctt1⁺ expression was increased significantly in response to oxidative stress but not osmostress.