Proteins in the Golgi membrane then stimulate the exchange of the GDP bound to ARF for GTP, and the COPI coat proteins bind to the ARF/GTP complex. Assembly of the coat is then followed by deformation of the membrane and vesicle budding. ARF then hydrolyzes its bound GTP, leading to the conversion of ARF to the GDP-bound state and the dissociation of coat proteins from the vesicle membrane.