Wsc1 is a member of a family of highly -glycosylated cell surface proteins that reside in the plasma membrane of and function as sensors of cell wall stress. These proteins activate the cell wall integrity signalling pathway by stimulating the small G-protein Rho1, protein kinase C (Pkc1) and a MAP kinase cascade. The cytoplasmic domains of Wsc1 family members interact with the Rom2 guanine nucleotide exchange factor to stimulate GTP-binding of Rho1. Here, a mutational analysis of the cytoplasmic domain of Wsc1 is presented. The data identify two regions of the Wsc1 cytoplasmic tail that are conserved with other family members as important for Rom2 interaction. These regions are separated by an inhibitory region, which includes a cluster of seryl residues that appear to be phosphorylated. Mutational analysis of these residues supports a model in which Wsc1 interaction with Rom2 is negatively regulated by phosphorylation.


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