Final answer:
Molecules to be packaged into vesicles for transport are selected by clathrin and other proteins. Cargo receptor proteins bind to specific packaged proteins, and with the help of clathrin, they bud off from the trans Golgi stack into separate vesicles. When the vesicles bind to complementary proteins on receiving membranes, the membranes fuse.
Step-by-step explanation:
The molecules to be packaged into vesicles for transport are selected by clathrin and other COP proteins, with the help of cargo receptor proteins. At the trans face of the Golgi vesicles, cargo receptor proteins bind to specific packaged proteins, and with the help of clathrin, they bud off from the trans Golgi stack into separate vesicles. These vesicles also acquire V-SNARE proteins. When V-SNARE proteins on the vesicles bind to complementary T-SNARE proteins on receiving membranes, the membranes fuse.