No abstract

Tethering factors have been shown to interact with Rabs and SNAREs and, more recently, with coat proteins. Coat proteins are required for cargo selection and membrane deformation to bud a transport vesicle from a donor compartment. It was once thought that a vesicle must uncoat before it recognizes its target membrane. However, recent findings have revealed a role for the coat in directing a vesicle to its correct intracellular destination. In this review we will discuss the literature that links coat proteins to vesicle targeting events.

Membrane budding and fusion occur in all eukaryotic cells. Their underlying mechanisms have been studied in mammalian neurons and in yeast, a simple eukaryote. The differences between these two systems would suggest that fusion events in yeast and the neuron would operate by different mechanisms, but recent advances indicate that this is not true.

TRAPP is a conserved protein complex required early in the secretory pathway. Here, we report two forms of TRAPP, TRAPP I and TRAPP II, that mediate different transport events. Using chemically pure TRAPP I and COPII vesicles, we have reconstituted vesicle targeting in vitro. The binding of COPII vesicles to TRAPP I is specific, blocked by GTPgammaS, and, surprisingly, does not require other tethering factors. Our findings imply that TRAPP I is the receptor on the Golgi for COPII vesicles. Once the vesicle binds to TRAPP I, the small GTP binding protein Ypt1p is activated and other tethering factors are recruited.