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. 2018 Apr 4;14(4):e7390. doi: 10.15252/msb.20167390

Figure 1. The signaling arm of the yeast pheromone response system (PRS).

Figure 1

Binding of the ligand, α‐factor, to a seven‐helix transmembrane receptor, Ste2, in the MATa cell depicted, causes the dissociation of the α subunit of a trimeric G‐protein, Gpa1, from the βγ dimer, Ste4/Ste18. This event causes the recruitment to the plasma membrane of the scaffold protein Ste5, leading to the assembly and activation of the MAP kinase cascade (MAPKKK Ste11, MAPKK Ste7) and the detachment from the scaffold of the Erk1/2‐like MAPKs Fus3 and Kss1 (Dohlman & Thorner, 2001). In the cytoplasm, activated Fus3 and Kss1 phosphorylate targets including Ste5 (Bhattacharyya et al, 2006; Malleshaiah et al, 2010), and in the nucleus, they phosphorylate Dig1, Dig2, and Ste12 (Tedford et al, 1997). These events comprise the pathway subsystem, P; that is, the subsystem that transmits the signal to the promoters of inducible genes. Activation of Ste12 leads to the induction of approximately 100 pheromone‐responsive genes (PRGs) (Roberts et al, 2000) and their expression via the expression subsystem G (defined in the text).