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. Author manuscript; available in PMC: 2014 Nov 1.
Published in final edited form as: Biochim Biophys Acta. 2013 Feb 15;1833(11):2464–2472. doi: 10.1016/j.bbamcr.2013.02.003

Figure 1. COPII assembly at the ER and regulation by cytosolic factors.

Figure 1

COPII coat formation at the ER is initiated by recruitment of Sar to the membrane in the GTP-bound state, enhanced by Sec12 GEF activity. Sar1-GTP recruits Sec23/24 heterodimer through interaction with Sec23. At the ER, Sec24 recruits cargo into pre-budding complexes. Sec13/31 complex is recruited to the inner coat layer through interactions with Sec23. Sec13/31 assembly into the coat drives membrane curvature, facilitating membrane deformation. Lumenal cargoes diffuse into the nascent bud or are recruited through cargo receptor proteins. Vesicle release from the ER is achieved in a manner related to Sar1 GTP hydrolysis. Released COPII vesicles typically fall within a 60 to 100 nanometer range. Sec16 facilitates COPII vesicle formation at the ER, likely through scaffolding COPII components and contributing to ERES structure. Interactions of COPII and COPII-associated components with domains of Sec16 are shown in the box in the upper left. Non-COPII proteins that affect COPII vesicle formation are shown in red italics, with red arrows indicating their proposed targets.