“…The HMH domain has a positive regulatory function, because deletion of the HMH domain renders both Hkr1 and Msb2 incapable of activating Hog1 in response to osmostress (29,30,33). We have recently shown that the HMH domains bind to the extracellular Cys-rich region of Opy2 (22,29). Opy2 is a single-path transmembrane protein whose cytoplasmic tail binds to the Ste50 adaptor protein (36,37).…”