GGAs: A family of ADP ribosylation factor-binding proteins related to adaptors and associated with the Golgi complex

Formation of intracellular transport intermediates and selection of cargo m olecules are mediated by protein coats associated with the cytosolic face o f membranes. Here, we describe a novel family of ubiquitous coat proteins t ermed GGAs, which includes three members in humans and two in yeast. GGAs h ave a modular structure consisting of a VHS domain, a region of homology te rmed GAT, a linker segment, and a region with homology to the ear domain of gamma-adaptins. Immunofluorescence microscopy showed colocalization of GGA s with Golgi markers, whereas immunoelectron microscopy of GGA3 revealed it s presence on coated vesicles and buds in the area of the TGN. Treatment wi th brefeldin A or overexpression of dominant-negative ADP ribosylation fact or 1 (ARF1) caused dissociation of GGAs from membranes. The GAT region of G GA3 was found to: target a reporter protein to the Golgi complex; induce di ssociation from membranes of ARF-regulated coats such as AP-1, AP-3, AP-4, and COPI upon overexpression; and interact with activated ARF1, Disruption of both GGA genes in yeast resulted in impaired trafficking of carboxypepti dase Y to the vacuole. These observations suggest that GGAs are components of ARF-regulated coats that mediate protein trafficking at the TGN.