Figure 1.

Anterograde vesicular transport between stable compartments. Secretory cargoes travel from the ER to the intermediate compartment (IC) and cis-Golgi in dissociative carriers. Golgi compartments are stable and biochemically distinct. Secretory cargoes move across the stack by means of COPI vesicles that bud from one compartment and fuse with the next, whereas resident Golgi proteins stay in place by being excluded from budding vesicles. This model does not provide a mechanism for transporting secretory cargoes that are too large to fit within COPI vesicles.