Adaptins are components of the adaptor complexes which link clathrin to receptors in coated vesicles. Clathrin-associated protein complexes are believed to interact with the cytoplasmic tails of membrane proteins, leading to their selection and concentration. The AP-1 complex interacts directly with clathrin. Adaptor protein complex 1 (AP-1) is a heterotetramer composed of two large adaptins (gamma-type subunit APL4 and beta-type subunit APL2), a medium adaptin (mu-type subunit APM1) and a small adaptin (sigma-type subunit APS1). Interacts with CHC1. Interacts with APM2, probably forming an alternative AP-1-like complex. Component of the coat surrounding the cytoplasmic face of coated vesicles in the plasma membrane. Present with 2690 molecules/cell in log phase SD medium. Belongs to the adaptor complexes large subunit family.