FIGURE 1: The Cdc42 GTPase and its regulators in budding yeast. Cdc42 activity is regulated by at least three types of regulators: the GEFs, Cdc24 and Bud3; the GAPs, Rga1, Rga2, Bem2, and Bem3; and the GDI Rdi1. These regulators are likely to mediate the regulation of Cdc42 in response to internal and external signals. Cdc42 regulates the organization of the actin and septin cytoskeletons and polarized secretion via its downstream effectors including PAKs.