Successive addition of Arf1 and coatomer to membrane sheets. Lipids containing the p23 lipopeptide were spotted on a glass surface in a chamber as described in Materials and methods and hydrated with buffer containing 1 mM GTP and 50 nM of the exchange factor ARNO. Time-lapse videos were recorded as described in the legend of Video 1. 1 µM Arf1 was injected, resulting in rapid formation of motile membrane tubules. Subsequently, 0.25 µM coatomer was added. There is an initial nonspecific loss of many tubular structures because of capillary flow forces after injection. Interestingly, however, the added coatomer leads to a stepwise shortening of the remaining Arf1-generated tubules as indicated by arrows (after addition of coatomer, the video is slowed down 2× for better clarity). As a second effect, new structures with a distinct morphology arise over the entire lipid surface (examples indicated by circles).
