The AP3 complex is a heterotetramer composed of two large adaptins (AP3D1, AP3B1 or AP3B2), a medium adaptin (AP3M1 or AP3M2) and a small adaptin (APS1 or AP3S2). The complex is associated with the Golgi region as well as more peripheral structures. It facilitates the budding of vesicles from the Golgi membrane and may be directly involved in trafficking to lysosomes. AP3M1 is highly homologous to AP3M2 but is the preferred binding partner to the YQRL motif from the cytosolic domain of TGN38. AP3M1 has also been shown to interact with the HIV-1 virulence protein Nef.