title: Sec16 defines endoplasmic reticulum exit sites and is required for secretory cargo export in mammalian cells.
abstract: The selective export of proteins and lipids from the endoplasmic reticulum (ER) is mediated by the coat protein complex II (COPII) that assembles onto the ER membrane. In higher eukaryotes, COPII proteins assemble at discrete sites on the membrane known as ER exit sites (ERES). Here, we identify Sec16 as the protein that defines ERES in mammalian cells. Sec16 localizes to ERES independent of Sec23/24 and Sec13/31. Overexpression, and to a lesser extent, small interfering RNA depletion of Sec16, both inhibit ER-to-Golgi transport suggesting that Sec16 is required in stoichiometric amounts. Sar1 activity is required to maintain the localization of Sec16 at discrete locations on the ER membrane, probably through preventing its dissociation. Our data suggest that Sar1-GTP-dependent assembly of Sec16 on the ER membrane forms an organized scaffold defining an ERES.
authors.affiliation: Department of Biochemistry, University of Bristol, School of Medical Sciences, University Walk, Bristol BS8 1TD, UK.
authors.forename: Peter
authors.initials: P
authors.lastname: Watson
authors.forename: Anna K
authors.initials: AK
authors.lastname: Townley
authors.forename: Pratyusha
authors.initials: P
authors.lastname: Koka
authors.forename: Krysten J
authors.initials: KJ
authors.lastname: Palmer
authors.forename: David J
authors.initials: DJ
authors.lastname: Stephens
mesh_terms: D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D015870:Gene Expression; D006056:Golgi Apparatus / Q000378:metabolism; D006801:Humans; D020559:Monomeric GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism; D011485:Protein Binding; D021381:Protein Transport; D033921:Vesicular Transport Proteins / Q000235:genetics / Q000378:metabolism*
chemical_list: C517555:SEC16A protein, human; D033921:Vesicular Transport Proteins; D020559:Monomeric GTP-Binding Proteins