Compartmentation of the Golgi complex: brefeldin-A distinguishes trans- Golgi cisternae from the trans-Golgi network

Several models have been proposed to explain BFA action. One possibility is that the target of BFA is associated with the ER. By blocking ER export, BFA might be uncovering a vesicular recycling pathway that functions between the Golgi and ER (9, 28, 29) . This model could easily explain why most Golgi enzymes are redistributed to the ER, if one assumes that each cisterna of the Golgi complex communicates with its proximal neighbor by shuttling transport vesicles. This model does not explain why TGN components do not return to the ER, because putative shuttling vesicles might be expected to move between the TGN and trans-Golgi as frequently as they traverse between transand medial Golgi cisternae. If the target of BFA is indeed the ER, our data would suggest that transport between the TGN and trans-Golgi cisternae differs significantly from transport between more proximal Golgi cisternae.