BREFELDIN-A INHIBITS GOLGI MEMBRANE-CATALYZED EXCHANGE OF GUANINE-NUCLEOTIDE ONTO ARF PROTEIN

THE fungal metabolite brefeldin A is a powerful tool for investigating membrane traffic in eukaryotic cells1. The effects of brefeldin A on traffic are partly explained by its ability to prevent binding of cytosolic coat proteins onto membranes2-5. The non-clathrin coatomer complex6,7 binds reversibly to Golgi membranes in a GTP-controlled cycle8-10. The low-molecular-mass GTP-binding protein ADP-ribosylation factor (ARF), which also associates reversibly with Golgi membranes11,12, is required for coatomer binding13 and probably accounts for the control by guanine nucleotide of the coatomer-membrane interaction. Brefeldin A prevents the assembly of coatomer onto the membrane by inhibiting the GTP-dependent interaction of ARF with the Golgi membrane13, but the nature of this interaction has not been established. Here we demonstrate that Golgi membranes can specifically catalyse the exchange of GTP onto ARF and that brefeldin A prevents this function.