Vesicular traffic within the early secretory pathway is mediated by COPI– and COPII–coated vesicles. While COPII–coated vesicles appear to be involved exclusively in the export of secretory proteins and lipids from the endoplasmic reticulum (ER), COPI–coated vesicles seem to function in both anterograde and retrograde transport between the ER–Golgi intermediate compartment (IC) and the Golgi as well as in intra–Golgi transport. Here, we focus on (i) the mechanisms how these transport carriers are formed from a given donor membrane; and (ii) the possible mechanisms involved in sorting of proteins and lipids into such transport vesicles.
