Packing of clathrin into coats.

Abstract

Clathrin is involved in the formation of coated vesicles, by budding, from cellular membranes of most eukaryotic cells. Coated membrane in pits and vesicles has long been recognized by the remarkable protein lattice present on the cytoplasmic surface of the membrane (see, e.g., Roth and Porter 1964). On shallow-coated pits the protein network is essentially a lattice of hexagonal units. As pentagons are introduced, the pit becomes more concave and the coat deforms inwards, until finally a vesicle is enclosed by a complete polyhedral coat (Kanaseki and Kadota 1969). Images of stages in the process of budding of vesicles from the cytoplasmic surface of fibroblast plasma membranes have recently been captured by rapid freezing and deep etching (Heuser 1980). After a vesicle has been pinched off inside the cell, the coat comes off, the vesicle is released for fusion with another cellular membrane, and the coat components are believed to...