Membrane traffic mediated by AP-1. (A) Simplified schematic of AP-1 in linking cargo to a clathrin-coated vesicle. AP-1 is a heterotetramer composed of β, γ, µ, and σ subunits. It contains multiple cargo-binding regions and binds clathrin and other accessory coat components to promote coat assembly. (B) Potential AP-1–mediated trafficking routes based on inhibition studies (blue arrows). At the TGN, AP-1 has been proposed to function to mediate traffic to the plasma membrane, endosomes, and recycling to the Golgi. At the endosome, AP-1 has been proposed to mediate traffic to the plasma membrane and to the TGN.