Isolation and characterization of a novel low molecular weight protein involved in intra-Golgi traffic.

Analysis of the cytosolic requirements for in vitro intra-Golgi transport led to the characterization of three proteins: N-ethylmaleimide-sensitive fusion protein (NSF), soluble NSF attachment protein (SNAP), and p115, all involved in the docking and fusion of transport vesicles to their target membranes. In the course of determining the minimal cytosolic requirements for intra-Golgi transport in vitro, we identified three additional factors that are sufficient to replace crude cytosol. We describe here the purification and characterization of one of these factors, a novel 16-kDa protein, p16, an essential factor for intra-Golgi protein transport. Based on transport activity, this purification procedure resulted in approximately 1,400-fold enrichment of p16 to apparent homogeneity. The activity of p16 could be observed in the absence of vesicle formation, suggesting that it may participate in the docking and fusion processes.