Figure 2.

Mpr1 is important for activation of Spc1 in response to oxidative stress. Wild-type (KS1376) and Δmpr1 (CA279) 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 (A) or oxidative stress induced by 0.3 mM H₂O₂ (B). 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. Δmpr1 mutant cells showed a significant defect in Spc1 activation upon oxidative stress, whereas osmostress induced strong activation of Spc1 in Δmpr1 mutants and wild-type cells.