Figure 10.

Model for the Sec4p signaling pathways. Secretory vesicles (V) carry the Rab GTPase Sec4p and its GEF Sec2p, which keeps Sec4p in its activated, GTP-bound state. Sec15p, a member of the exocyst complex, is one effector for Sec4p, and the interaction of these two proteins is required for the assembly of this complex and its tethering function in exocytosis (Guo et al., 1999b). Sec1p interacts with the exocyst (Wiederkehr et al., 2004) and binds to assembled SNARE complexes, possibly stabilizing them (Carr et al., 1999). Another effector of Sec4p, Sro7p (this study), interacts with the exocytic t-SNARE Sec9p (Lehman et al., 1999), and genetic data indicate that this interaction is required for Sec4p's role in exocytosis (Brennwald et al., 1994; Lehman et al., 1999; and this study). A recent study showed that the exocyst and the yeast lgl family members interact (Zhang et al., 2005), allowing an integrated response. Arrows indicate physical interactions.