Subunit of clathrin-associated adaptor protein complex 1 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. In association with AFTPH/aftiphilin in the aftiphilin/p200/gamma-synergin complex, involved in the trafficking of transferrin from early to recycling endosomes, and the membrane trafficking of furin and the lysosomal enzyme cathepsin D between the trans-Golgi network (TGN) and endosomes (By similarity). Adaptor protein complex 1 (AP-1) is a heterotetramer composed of two large adaptins (gamma-type subunit AP1G1 and beta-type subunit AP1B1), a medium adaptin (mu-type subunit AP1M1 or AP1M2) and a small adaptin (sigma-type subunit AP1S1 or AP1S2 or AP1S3) (By similarity). Interacts (via GAE domain) with RABEP1 (By similarity). Interacts with EPS15 (By similarity). Interacts with SYNRG/gamma-synergin (By similarity). Interacts (via GAE domain) with AP1AR (via coiled-coil domain) (By similarity). Interacts with CLN3 (via dileucine motif); this interaction facilitates lysosomal targeting (By similarity). Interacts (via GAE domain) with AFTPH/aftiphilin; the interaction is required to recruit AFTPH/aftiphilin to the perinuclear region of the cell (By similarity). Component of the coat surrounding the cytoplasmic face of coated vesicles located at the Golgi complex (By similarity). Co-localizes with AFTPH/aftiphilin in the cytoplasm (By similarity). Belongs to the adaptor complexes large subunit family.