ARF alternates between GTP-bound and GDP-bound states. When bound to GDP, ARF associates with the membrane of the trans Golgi network, where guanine nucleotide exchange factors (GEF) promote the exchange of the bound GDP for GTP. In its GTP-bound state, ARF promotes the binding of COPI coat protein (coatomer), leading to vesicle budding. Hydrolysis of the bound GTP then converts ARF to the GDP-bound state, leading to disassembly of the vesicle coat prior to fusion with the target membrane.