1. Howard Hughes Medical Institute and the,
2. Department of Cell Biology Yale University School of Medicine, New Haven, Connecticut 06519, USA
3. Division of Biological Sciences, The University of Montana, Missoula, Montana 59812-4824, USA

Correspondence to: Susan Ferro-Novick^1,2 Correspondence and requests for materials should be addressed to S.F.-N. (Email: susan.ferronovick@yale.edu).

Abstract

The budding of endoplasmic reticulum (ER)-derived vesicles is dependent on the COPII coat complex¹. Coat assembly is initiated when Sar1-GTP recruits the cargo adaptor complex, Sec23/Sec24, by binding to its GTPase-activating protein (GAP) Sec23 (ref. 2). This leads to the capture of transmembrane cargo by Sec24 (refs 3, 4) before the coat is polymerized by the Sec13/Sec31 complex⁵. The initial interaction of a vesicle with its target membrane is mediated by tethers⁶. We report here that in yeast and mammalian cells the tethering complex TRAPPI (ref. 7) binds to the coat subunit Sec23. This event requires the Bet3 subunit. In vitro studies demonstrate that the interaction between Sec23 and Bet3 targets TRAPPI to COPII vesicles to mediate vesicle tethering. We propose that the binding of TRAPPI to Sec23 marks a coated vesicle for fusion with another COPII vesicle or the Golgi apparatus. An implication of these findings is that the intracellular destination of a transport vesicle may be determined in part by its coat and its associated cargo.

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