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. 2013 Oct 16;8(10):e77487. doi: 10.1371/journal.pone.0077487

Figure 1. Schematic representation of Ras1 signaling cascades.

Figure 1

Ras1 signals via two distinct effectors to control of both pheromone-inducible and routine cell growth pathways. In the absence of pheromone the GEF, Efc25 promotes GDP for GTP exchange on Ras1. Through a complex with a Rho-GEF, Scd1, Ras1-GTP activates the essential G protein, Cdc42 so allowing polarized cell growth, faithful chromosome segregation and cell division. A second GEF for Cdc42, Gef1, is required to initiate bipolar growth but is not activated by Ras1. Upon pheromone stimulation, Ras1 activation is increased through interaction with another Ras1-GEF, Ste6. This pool of Ras1-GTP propagates the transcriptional response (acting via a second effector, Byr2 and a MAPK cascade). Pheromone-activated Ras1 also induces further GTP exchange on Cdc42 through activation of Scd1 promoting unidirectional cell growth towards a mating partner. Ras1 and Cdc42 contain a slow intrinsic ability to hydrolyze GTP, but the reaction is accelerated through interaction with GAPs, Gap1 and Rga4 (shown in red). Cross-talk between the two pathways is highlighted with dashed arrows.