Fig. 2. The core machinery of COPI recruitment to membranes, coat polymerization, vesicular budding and uncoating. Recruitment of coat proteins is initiated by ARF-GDP binding to p23 (1). Upon nucleotide exchange, ARF-GTP dissociates from p23 resulting in its stable association with the membrane (2). Multiple cycles of GTP hydrolysis and GDP to GTP exchange are likely to occur (grey box, see text for details), possibly causing rearrangements of p23/p24 oligomers (3). The products of these processes are ARF-GTP and presumably a p23/p24 heterooligomer, which triggers coatomer binding and coat polymerization (4). Following budding (5), the catalytic domain of ARF-GAP is sufficient to trigger uncoating (6). Active components are shown in green; inactive components are shown in red.

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