Subunit of clathrin-associated adaptor protein complex that plays a role in protein sorting in the late-Golgi/trans-Golgi network (TGN) and/or endosomes. The AP complexes mediate both the recruitment of clathrin to membranes and the recognition of sorting signals within the cytosolic tails of transmembrane cargo molecules (By similarity). Adaptor protein complexes are heterotetramers composed of two large adaptins (beta-type subunit and alpha-type or delta-type or epsilon-type or gamma-type subunit), a medium adaptin (mu-type subunit) and a small adaptin (sigma-type subunit) (By similarity). Interacts with AHK2. Associated with the trans-Golgi network. Component of the coat surrounding the cytoplasmic face of coated vesicles located at the Golgi complex (By similarity). A number of isoforms are produced. According to EST sequences. Belongs to the adaptor complexes large subunit family.