Fig. 10. Hog1 phosphorylation of Sko1 is critical for salt stress resistance. Yeast Δsko1 mutant cells (MAP19) were transformed with vector control pYEX-4T, GST–SKO1 (wild type), GST–SKO1(E) (mutant in the Hog1 phosphorylation sites), GST–SKO1(M) (mutant in the PKA phosphorylation sites) or GST–SKO1(EM) (mutant in both Hog1 and PKA phosphorylation sites) alleles. Overexpression of the GST fusions was achieved by addition of CuSO₄ to a final concentration of 0.3 mM to the plates. Serial dilutions of the transformed yeast strains were spotted onto SD plates lacking uracil containing or not 0.4 M NaCl as indicated.