FIG. 1.

Protein phosphatase inactivation of the HOG pathway. The HOG pathway is regulated by two membrane-bound osmosensors, Sln1 and Sho1. Both Sln1 and Sho1 activate the MAPK cascade (boxed). The two-component regulators, Sln1, Ypd1, and Ssk1, negatively regulate the two MEKKs, Ssk2 and Ssk22, while Sho1, Ste20, and Ste50 positively regulate the MEKK, Ste11. The MEKKs activate a MEK, Pbs2, and the MAPK, Hog1. Two protein tyrosine phosphatases, Ptp2 and Ptp3, inactivate Hog1 by dephosphorylating the pY residue in the phosphorylation lip, while the type 2C Ser/Thr phosphatase, Ptc1, dephosphorylates the pT residue in the phosphorylation lip.