Rab1 recruitment of p115 into a cis-SNARE complex: Programming budding COPII vesicles for fusion

The guanosine triphosphatase Rab1 regulates the transport of newly synthesi zed proteins from the endoplasmic reticulum to the Golgi apparatus through interaction with effector molecules, but the molecular mechanisms by which this occurs are unknown. Here, the tethering factor p115 was shown to be a Rab1 effector that binds directly to activated Rab1. Rab1 recruited p115 to coat protein complex II (COPII) vesicles during budding from the endoplasm ic reticulum, where it interacted with a select set of COPII vesicle-associ ated SNAREs (soluble N-ethylmateimide-sensitive factor attachment protein r eceptors) to form a cis-SNARE complex that promotes targeting to the Golgi apparatus. We propose that Rab1-regulated assembly of functional effector-S NARE complexes defines a conserved molecular mechanism to coordinate recogn ition between subcellular compartments.