Coat protein that is involved in the localization of trans- Golgi network (TGN) membrane proteins that contain acidic cluster sorting motifs. Controls the endosome-to-Golgi trafficking of furin and mannose-6-phosphate receptor by connecting the acidic-cluster- containing cytoplasmic domain of these molecules with the adapter- protein complex-1 (AP-1) of endosomal clathrin-coated membrane pits. Involved in HIV-1 nef-mediated removal of MHC-I from the cell surface to the TGN. Required for normal ER Ca2+ handling in lymphocytes. Together with WDR37, it plays an essential role in lymphocyte development, quiescence and survival. Required for stabilizing peripheral lymphocyte populations (By similarity). {ECO:0000250|UniProtKB:Q8K212, ECO:0000269|PubMed:11331585, ECO:0000269|PubMed:15692563}. This is the function of Ensembl gene identifier ENSG00000175115 (PACS1, phosphofurin acidic cluster sorting protein 1).