Clathrin heavy chain proteins are composed of several functional domains, including a carboxy-terminal region that permits interaction with other heavy chain proteins within a triskelion, and a globular amino-terminal region that associates with other vesicle proteins. Adaptor proteins, such as AP2, epsin and EPS15, are responsible for the recruitment of vesicle proteins to sites of pit formation and the assembly of the clathrin-coated vesicle.