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. 2003 Dec 18;23(2):302–311. doi: 10.1038/sj.emboj.7600036

Figure 1.

Figure 1

Activation of the HOG MAPK pathway and its negative regulation by protein phosphatases. (A) The yeast stress-activated HOG MAPK pathway contains a three-kinase cascade, which comprises the Ssk2, Ssk22 and Ste11 MEKKs, the Pbs2 MEK and the Hog1 MAPK. The Sln1-Ypd1-Ssk1 branch negatively regulates the Ssk2/22 MEKKs, while Sho1 positively regulates the Ste11 MEKK. Two classes of phosphatases regulate Hog1, which requires phosphorylation of Thr and Tyr in the sequence TGY for activation. Ptp2 and Ptp3 dephosphorylate pY, while Ptc1, Ptc2 and Ptc3 dephosphorylate pT. (B) Ptc1 but neither Ptc2 nor Ptc3 co-precipitates with Nbp2. The ability of Ptc1, Ptc2 and Ptc3 to associate with Nbp2 was examined in the nbp2Δ strain JHM17 expressing GST-PTCs and Nbp2-HA. Yeast were cultured, lysed, and co-precipitation assays performed as described in Materials and methods. The bound material was examined by SDS–PAGE and immunoblotting with anti-GST and anti-HA antibodies. The amount of Nbp2-HA in the lysate is also shown.