A yeast DNA J protein required for uncoating of clathrin-coated vesicles in vivo

Clathrin-coated vesicles mediate diverse processes such as nutrient uptake, downregulation of hormone receptors, formation of synaptic vesicles, virus entry, and transport of biosynthetic proteins to lysosomes. Cycles of coat assembly and disassembly are integral features of clathrin-mediated vesicu lar transport (Fig. la). Coat assembly involves recruitment of clathrin tri skelia, adaptor complexes and other factors that influence coat assembly, c argo sequestration, membrane invagination and scission(1-3) (Fig. 1a). Coat disassembly is thought to be essential for fusion of vesicles with target membranes and for recycling components of clathrin coats to the cytoplasm f or further rounds of vesicle formation. In vitro, cytosolic heat-shock prot ein 70 (Hsp70) and the J-domain co-chaperone auxilin catalyse coat disassem bly(4). However, a specific function of these factors in uncoating in vivo has not been demonstrated, leaving the physiological mechanism and signific ance of uncoating unclear. Here we report the identification and characteri zation of a Saccharomyces cerevisiae J-domain protein, Aux1. Inactivation o f Aux1 results in accumulation of clathrin-coated vesicles, impaired cargo delivery, and an increased ratio of vesicle-associated to cytoplasmic clath rin. Our results demonstrate an in vivo uncoating function of a J domain cc -chaperone and establish the physiological significance of uncoating in tra nsport mediated by clathrin-coated vesicles.