Coordination of individual vesicular transport steps by GTPases and their accessory factors: (A) The mammalian Golgin p115 interacts with GBF1, a GEF for Arf GTPase, as well as Rab1 GTPase, and SNAREs, to coordinate formation, tethering and fusion of ER-to-Golgi vesicles, respectively. (B) In yeast, Ypt31/32 GTPases regulate trans-Golgi vesicle formation and interact with the Myo2 motor and Sec2, the GEF for Sec4 GTPase. This cascade of interactions coordinates Golgi-to-PM vesicle formation, motility and targeting. Machinery components needed for the vesicular transport steps are shown in the boxes: coats drive cargo selection and vesicle formation at the donor compartment; motors (e.g., myosin) move vesicles on the cytoskeleton (e.g., actin); tethering factors mediate vesicle docking at the acceptor compartment; SNAREs (i.e., v-SNARE and t-SNARE) facilitate membrane fusion.