COPI IN ER GOLGI AND INTRA-GOLGI TRANSPORT - DO YEAST COPI MUTANTS POINT THE WAY/

Coat complexes facilitate the formation of transport vesicles which ar e essential for proper trafficking of protein and lipids through the s ecretory pathway. Since its initial identification in the mid-1980s, t he COPI coat complex has been credited with mediating multiple distinc t transport events and intracellular processes in the exocytic pathway . Not surprisingly, the diversity of these functions has led to signif icant debate concerning the primary function of COPI. Specifically, wi thin the ER/Golgi and intra-Golgi systems, does COPI mediate anterogra de protein transport, retrograde protein transport, or both? This revi ew will focus on the in vivo roles of COPI, primarily examining data f rom studies of yeast COPI mutants but also including evidence from mam malian systems as appropriate. Some of the current controversies surro unding whether COPI acts directly or indirectly in anterograde and ret rograde transport will also be addressed. Because recruitment of COPI to membranes requires the small GTP-binding protein ARF, we will also discuss ARF and proteins that regulate ARF function, and how these pro teins might modulate both COPI-driven events and overall membrane comp osition. Finally, we will point out some of the links still missing fr om our understanding of COPI-driven events and discuss possible future directions for studies of COPI function. (C) 1998 Elsevier Science B, V. All rights reserved.