Figure 8.

Model of yeast Golgi-to-endosome vesicle-mediated protein transport. Golgi-modified p2 CPY is bound by the sorting receptor Vps10p and packaged into transport vesicles that bud from the Golgi. The v-SNARE Vti1p and the GTPase Vps21p that has been activated by the Vps21p exchange factor Vps9p are present on these vesicles as they move through the cytoplasm to the prevacuolar endosomal compartment. Vac1p then interacts with activated GTP-bound Vps21p on the vesicle and also with Vps45p that is peripherally associated with the endosome via the t-SNARE homologue Pep12p. These interactions may be regulated by PtdIns(3)P. The signal transduced from activated Vps21p through Vac1p and Vps45p enables the t-SNARE homologue Pep12p to interact with Vti1p to promote vesicle fusion.