Editing COPII (section)

==Function==
The COPII coat is responsible for the formation of vesicles from the endoplasmic reticulum (ER). These vesicles transport cargo proteins to the Golgi apparatus (in yeast) or the endoplasmic-reticulum-Golgi intermediate compartment (ERGIC, in mammals).<ref name=Peotter2019/>

Coat assembly is initiated when the [[cytosol]]ic [[Ras GTPase]] Sar1 is activated by its [[guanine nucleotide exchange factor]] Sec12.<ref name=Peotter2019/> Activated Sar1-GTP inserts itself into the ER membrane, binding preferentially to areas of membrane curvature. As Sar1-GTP inserts into the membrane, it recruits Sec23 and Sec24 to make up the inner cage.<ref name=Peotter2019/> Once the inner coat is assembled, the outer coat proteins Sec13 and Sec31 are recruited to the budding vesicle.<ref name=Peotter2019/> Hydrolysis of the Sar1 GTP to GDP promotes disassembly of the coat.

Some proteins are found to be responsible for selectively packaging cargos into COPII vesicles. More recent research suggests the Sec23/Sec24-Sar1 complex participates in cargo selection.{{r|Fath 2007}} For example, Erv29p in ''Saccharomyces cerevisiae'' is found to be necessary for packaging glycosylated pro-α-factor.<ref name="pmid11711675">{{cite journal | vauthors = Belden WJ, Barlowe C | title = Role of Erv29p in collecting soluble secretory proteins into ER-derived transport vesicles | journal = Science | volume = 294 | issue = 5546 | pages = 1528–31 | date = November 2001 | pmid = 11711675 | doi = 10.1126/science.1065224 | bibcode = 2001Sci...294.1528B | s2cid = 29870942 }}</ref>

Sec24 proteins recognize various cargo proteins, packaging them into the budding vesicles.