Ubiquitination drives COPI priming and Golgi SNARE localization
Deciphering mechanisms controlling SNARE localization within the Golgi complex is crucial to understanding protein trafficking patterns within the secretory pathway. SNAREs are also thought to prime COPI assembly to ensure incorporation of these essential cargoes into vesicles but the regulation of these events is poorly understood. Here we report a roles for ubiquitin recognition by COPI in SNARE trafficking and in stabilizing interactions between Arf, COPI, and Golgi SNAREs. The ability of COPI to bind ubiquitin through its N-terminal WD repeat domain of {beta}COP or through an unrelated ubiquitin-binding domain (UBD) is essential for the proper localization of Golgi SNAREs Bet1 and Gos1. We find that COPI, the ArfGAP Glo3 and multiple Golgi SNAREs are ubiquitinated. Notably, the binding of Arf and COPI to Gos1 is markedly enhanced by ubiquitination of these components. Glo3 is thought to prime COPI-SNARE interactions; however, Glo3 is not enriched in the ubiquitin-stabilized SNARE-Arf-COPI complex but is instead enriched with COPI complexes that lack SNAREs. These results support a new model for how posttranslational modifications drive COPI priming events crucial for Golgi SNARE localization.