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. Author manuscript; available in PMC: 2009 Nov 16.
Published in final edited form as: Cell. 2009 Mar 20;136(6):1085–1097. doi: 10.1016/j.cell.2009.01.049

Figure 1. Ste5 scaffold protein is required for mating pathway signaling.

Figure 1

(A) The MAPKKK Ste11 and MAPKK Ste7 function in both the mating and filamentation pathways in yeast. Ste7 must select the appropriate MAPK to phosphorylate in response to input (Fus3 for α-factor, and Kss1 in response starvation). (B) During mating, stimulation with α-factor leads primarily to phosphorylation of Fus3. This reaction requires the scaffold protein Ste5. Starvation input specifically induces the filamentation response through phosphorylation of Kss1. The Ste5 scaffold is not required for filamentation. (C) Expression of a constitutively active allele of MAPKKK Ste11 in a strain lacking Ste5 results only in Kss1 phosphorylation (both Kss1 and Fus3 phosphorylation are observed in strains with Ste5), further indicating that the Ste5 scaffold is required, in vivo, for Ste11➔Ste7➔Fus3 signaling (Flatauer et al., 2005).