A cycle of clathrin assembly and disassembly drives the formation of coated vesicles, intermediates in intracellular protein transport. The heavy chain of clathrin is needed for assembly, but the function of the clathrin light chains has remained obscure. An enzyme has now been purified which uses ATP hydrolysis to power the release of clathrin from coated vesicles, presumably recycling the coat protein for repeated rounds of vesicle budding. This 'uncoating ATPase' requires clathrin light chains for its action. © 1984 Nature Publishing Group.