Brefeldin A (BFA) is a macrocyclic lactone that inhibits protein secretion and disrupts the Golgi apparatus, leading to the formation of membrane tubules and the mixing of Golgi and ER membranes. BFA treatment causes the Golgi apparatus to disassemble and mix with the ER, with Golgi-derived tubules extending along microtubules. These tubules facilitate the retrograde transport of Golgi membrane into the ER. BFA also induces tubules in other peripheral organelles, such as endosomes and lysosomes, but not in the Golgi apparatus of some cells. BFA inhibits the assembly of cytosolic proteins onto Golgi membranes, including β-COP and ARF, and this inhibition is regulated by GTP-binding proteins. The effects of BFA on membrane traffic suggest that it disrupts the normal retrograde pathway from the Golgi to the ER, leading to changes in membrane trafficking and organelle structure. BFA also affects the sorting of proteins and the formation of transport vesicles, and its effects are modulated by the presence of GTP and other factors. The study of BFA has provided insights into the mechanisms of membrane traffic and organelle structure, highlighting the importance of cytosolic coat proteins in regulating membrane transport. BFA has also raised questions about the role of trimeric G proteins in membrane traffic and the regulation of organelle dynamics. Overall, BFA has been a valuable tool in understanding the complex processes of membrane traffic and organelle structure in eukaryotic cells.Brefeldin A (BFA) is a macrocyclic lactone that inhibits protein secretion and disrupts the Golgi apparatus, leading to the formation of membrane tubules and the mixing of Golgi and ER membranes. BFA treatment causes the Golgi apparatus to disassemble and mix with the ER, with Golgi-derived tubules extending along microtubules. These tubules facilitate the retrograde transport of Golgi membrane into the ER. BFA also induces tubules in other peripheral organelles, such as endosomes and lysosomes, but not in the Golgi apparatus of some cells. BFA inhibits the assembly of cytosolic proteins onto Golgi membranes, including β-COP and ARF, and this inhibition is regulated by GTP-binding proteins. The effects of BFA on membrane traffic suggest that it disrupts the normal retrograde pathway from the Golgi to the ER, leading to changes in membrane trafficking and organelle structure. BFA also affects the sorting of proteins and the formation of transport vesicles, and its effects are modulated by the presence of GTP and other factors. The study of BFA has provided insights into the mechanisms of membrane traffic and organelle structure, highlighting the importance of cytosolic coat proteins in regulating membrane transport. BFA has also raised questions about the role of trimeric G proteins in membrane traffic and the regulation of organelle dynamics. Overall, BFA has been a valuable tool in understanding the complex processes of membrane traffic and organelle structure in eukaryotic cells.