FIG 10.

Proposed two-step activation mechanism of the Hog1 MAPK pathway. In activation step 1, increased external osmolarity induces conformational changes in the complex formed between the Msb2 HMH domain and the Opy2 CR domain. This conformational change is transmitted across the plasma membrane (PM) to induce an interaction between the associated Ste20 and Ste11 kinases. In activation step 2, increased osmolarity induces structural changes in the Sho1 TM domains, resulting in an increased interaction between Ste11 and Pbs2 (9).