Protein sorting by directed maturation of Golgi compartments.

How does the Golgi stack mediate transport of cargo from the endoplasmic reticulum (ER) to the cell surface? A possibility is that cargo-containing vesicles derived from the ER form early Golgi compartments that then mature by retrieval of processing enzymes from later Golgi compartments. Maturation continues at terminal Golgi compartments by retrieval of transport components from the endocytic pathway to promote sorting of cargo to multiple cellular destinations. Hence, retrograde movement may integrate exocytic and endocytic pathways in eukaryotic cells and coordinate membrane flow and cargo transport through the Golgi stack.