Orylation was not detected in the ste11Dssk2Dssk22D mutant. D. Hog1p phosphorylation assay under ionic osmotic stress in the ssk1Dste11D double mutant. Cells were exposed to a different levels of salt stress induced by NaCl (concentration shown) in YPD medium for the time indicated. E. Same as in D but for the wild type cells. F. The ssk1Dste11D mutant exhibited better growth than hog1D mutant under osmotic stress. Serial dilutions (from left to right in each panel) of indicated strains were spotted onto YPD and salt plates and growth was scored after 3 days. doi:10.1371/journal.pone.0054867.ga high variable 1531364 N-terminal segment (177,240) in Ssk22p. Previous study has identified the Ssk1p binding domain (294,413) in Ssk2p [7]. We assume that the binding site for the X factor is located in the near N-terminal region.To determine the region in Ssk2p that is essential for its activation in the absence of Ssk1p, various segments near the Title Loaded From File Nterminus were deleted in Ssk2p. These constructs were transformed into the host strains ste11Dssk2Dssk22D and ste11Dssk1Dssk2D to test the activation of Hog1p, with resultsAlternative Activation of Ssk2p in Osmotic StressFigure 2. Ssk2p can be activated independent of Ssk1p under severe osmotic stress. A. Hog1p was Title Loaded From File phosphorylated in the ste11Dssk1Dssk22D mutant under severe osmotic stress (higher than 0.5 M sorbitol). B. Hog1p could not be phosphorylated in the ste11Dssk1Dssk2D mutant under 0.4 M or 1.0 M sorbitol. C. Actin disassembly did not activate the HOG pathway through Ssk2p. Within Lat B treatment, wild type strain and ste11Dssk1D mutant did not display activation of Hog1p. D.The effect of Lat B on actin structures in yeast cells. Rd-phalloidin was used to observe the effects of Lat B addition to yeast cells. Both the wild type cells and ste11Dssk1D mutant cells were incubated in the absence of Lat B and for 20 min in the presence of 200 mM Lat B. E. The osmosensitivity phenotype of budding yeast HOG pathway mutants. Serial dilutions (from left to right in each panel) of indicated strains were spotted onto YPD and salt plates and growth was scored after 3 days. doi:10.1371/journal.pone.0054867.gAlternative Activation of Ssk2p in Osmotic StressFigure 3. Comparison of protein sequences of Ssk2p and Ssk22p. The alignment was carried out by software Vector NTI 10. doi:10.1371/journal.pone.0054867.gshown in Figures 4A and 4B. A mutant lacking the region (1,176) was able to activate the Hog1p in both the mutant hosts ste11Dssk2Dssk22D and ste11Dssk1Dssk2D. The mutant lacking segment of amino acid 1,240 could activate the Hog1p in the ste11Dssk2Dssk22D but not in the host ste11Dssk1Dssk22D. Besides, the mutant lacking the region of amino acid 177,239 could activate the HOG pathway in the ste11Dssk2Dssk22D 24786787 but not in the host ste11Dssk1Dssk22D. The phenotype of Ssk2D(177,239) cells is similar to that of the Ssk2D(1,240) cells (Figure 4E). As the growthassay in Figures 4C and 4E show, the ssk2D(1,176) mutant in both hosts had no discernible effect on growth on high osmolarity media. The ssk2D(1,240) mutant and ssk2D(177,239) mutant in ste11Dssk1Dssk22D were osmosensitive, but not in the ste11Dssk2Dssk22D. These results suggest that the N- terminal portion of Ssk2p (amino acids 177?40) is indeed required for the activation of Ssk2p by the X factor under osmotic stress (Figure 4C). The segment is close to the Ssk1p BD (294,413) (Figure 4 D). PreviousAlternative Activation of Ssk2p in Osmotic StressFigure 4. A r.Orylation was not detected in the ste11Dssk2Dssk22D mutant. D. Hog1p phosphorylation assay under ionic osmotic stress in the ssk1Dste11D double mutant. Cells were exposed to a different levels of salt stress induced by NaCl (concentration shown) in YPD medium for the time indicated. E. Same as in D but for the wild type cells. F. The ssk1Dste11D mutant exhibited better growth than hog1D mutant under osmotic stress. Serial dilutions (from left to right in each panel) of indicated strains were spotted onto YPD and salt plates and growth was scored after 3 days. doi:10.1371/journal.pone.0054867.ga high variable 1531364 N-terminal segment (177,240) in Ssk22p. Previous study has identified the Ssk1p binding domain (294,413) in Ssk2p [7]. We assume that the binding site for the X factor is located in the near N-terminal region.To determine the region in Ssk2p that is essential for its activation in the absence of Ssk1p, various segments near the Nterminus were deleted in Ssk2p. These constructs were transformed into the host strains ste11Dssk2Dssk22D and ste11Dssk1Dssk2D to test the activation of Hog1p, with resultsAlternative Activation of Ssk2p in Osmotic StressFigure 2. Ssk2p can be activated independent of Ssk1p under severe osmotic stress. A. Hog1p was phosphorylated in the ste11Dssk1Dssk22D mutant under severe osmotic stress (higher than 0.5 M sorbitol). B. Hog1p could not be phosphorylated in the ste11Dssk1Dssk2D mutant under 0.4 M or 1.0 M sorbitol. C. Actin disassembly did not activate the HOG pathway through Ssk2p. Within Lat B treatment, wild type strain and ste11Dssk1D mutant did not display activation of Hog1p. D.The effect of Lat B on actin structures in yeast cells. Rd-phalloidin was used to observe the effects of Lat B addition to yeast cells. Both the wild type cells and ste11Dssk1D mutant cells were incubated in the absence of Lat B and for 20 min in the presence of 200 mM Lat B. E. The osmosensitivity phenotype of budding yeast HOG pathway mutants. Serial dilutions (from left to right in each panel) of indicated strains were spotted onto YPD and salt plates and growth was scored after 3 days. doi:10.1371/journal.pone.0054867.gAlternative Activation of Ssk2p in Osmotic StressFigure 3. Comparison of protein sequences of Ssk2p and Ssk22p. The alignment was carried out by software Vector NTI 10. doi:10.1371/journal.pone.0054867.gshown in Figures 4A and 4B. A mutant lacking the region (1,176) was able to activate the Hog1p in both the mutant hosts ste11Dssk2Dssk22D and ste11Dssk1Dssk2D. The mutant lacking segment of amino acid 1,240 could activate the Hog1p in the ste11Dssk2Dssk22D but not in the host ste11Dssk1Dssk22D. Besides, the mutant lacking the region of amino acid 177,239 could activate the HOG pathway in the ste11Dssk2Dssk22D 24786787 but not in the host ste11Dssk1Dssk22D. The phenotype of Ssk2D(177,239) cells is similar to that of the Ssk2D(1,240) cells (Figure 4E). As the growthassay in Figures 4C and 4E show, the ssk2D(1,176) mutant in both hosts had no discernible effect on growth on high osmolarity media. The ssk2D(1,240) mutant and ssk2D(177,239) mutant in ste11Dssk1Dssk22D were osmosensitive, but not in the ste11Dssk2Dssk22D. These results suggest that the N- terminal portion of Ssk2p (amino acids 177?40) is indeed required for the activation of Ssk2p by the X factor under osmotic stress (Figure 4C). The segment is close to the Ssk1p BD (294,413) (Figure 4 D). PreviousAlternative Activation of Ssk2p in Osmotic StressFigure 4. A r.
