Plasma membrane signaling mucin that promotes activation of the MAPK for the filamentous growth pathway. Partially redundant with the SHO1 osmosensing branch for the activation of STE11. Interacts with CDC42 and SHO1. localized to polarized sites on the cell surface. O-glycosylated in the Ser/Thr-rich regions. Present with 1320 molecules/cell in log phase SD medium. Belongs to the HKR1/MSB2 family.