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Nature Cell Biology 3, 531–537 (1 June 2001) | doi:10.1038/35078500

Dynamics of the COPII coat with GTP and stable analogues

Bruno Antonny , David Madden , Susan Hamamoto , Lelio Orci & Randy Schekman

We have developed an assay to monitor the assembly of the COPII coat onto liposomes in real time. We show that with Sar1pGTP bound to liposomes, a single round of assembly and disassembly of the COPII coat lasts a few seconds. The two large COPII complexes Sec23/24p and Sec13/31p bind almost instantaneously (in less than 1 s) to Sar1pGTP-doped liposomes. This binding is followed by a fast (less than 10 s) disassembly due to a 10-fold acceleration of the GTPase-activating protein activity of Sec23/24p by the Sec13/31p complex. Experiments with the phosphate analogue BeFx suggest that Sec23/24p provides residues directly involved in GTP hydrolysis on Sar1p.