BIDIRECTIONAL TRANSPORT BY DISTINCT POPULATIONS OF COPI-COATED VESICLES

Electron microscope immunocytochemistry reveals that both anterograde- directed (proinsulin and VSV G protein) and retrograde-directed (the K DEL receptor) cargo are present in coPI-coated vesicles budding from e very level of the Golgi stack in whole cells; however, they comprise t wo distinct populations that together can account for at least 80% of the vesicles budding from Golgi cisternae. Segregation of antero-grade - from retrograde-directed cargo into distinct sets of COPI-coated ves icles is faithfully reproduced in the cell-free Golgi transport system , in which VSV G protein and KDEL receptor are packaged into separable vesicles, even when budding is driven by highly purified coatomer and a recombinant ARF protein.