Sequential Tethering of Golgins and Catalysis of SNAREpin Assembly by the Vesicle-Tethering Protein p115

p115 tethers coat protein (COP)I vesicles to Golgi membranes. The acidic COOH-terminal domain of p115 links the Golgins, Giantin on COPI vesicles, to GM130 on Golgi membranes. We now show that a SNARE motif-related domain within p115 stimulates the specific assembly of endogenous Golgi SNAREpins containing the t-SNARE, syntaxin 5. p115 catalyzes the construction of a cognate GOS-28-syntaxin-5 (v-/t-SNARE) complex by first linking the SNAREs to promote their direct interaction. These events are essential for NSF-catalyzed reassembly of postmitotic Golgi vesicles and tubules into mature cisternae. Staging experiments reveal that the linking of Golgins precedes SNAREpin assembly. Thus, p115 coordinates sequential tethering and docking of COPI vesicles by first using long tethers (Golgins) and then short tethers (SNAREs).