A receiver domain (amino acids 177∼240) near the N-terminus of SSK2 is needed for the activation of SSK2 independent of SSK1.

A. Three mutants ssk2Δ^(1–176), ssk2Δ^(1–240), ssk2Δ^(177–239) and wild type Ssk2 were expressed in ste11Δssk1Δssk2Δ mutant, and the Hog1p phosphorylation was determined under osmotic stress. B. Three mutants ssk2Δ^(1–176), ssk2Δ^(1–240), ssk2Δ^(177–239) and wild type Ssk2 were expressed in ste11Δssk2Δssk22Δ mutant, and the Hog1p phosphorylation was determined under osmotic stress. C. The osmosensitivity of the mutants of Ssk2p. D. N- terminal portion of Ssk2p (amino acid 177–240) is required for the activation of Ssk2p by the X factor under osmotic stress.