This gene encodes a member of the adaptor-related protein complex 1, sigma subunit genes. The encoded protein is a component of adaptor protein complex 1 (AP-1), one of the AP complexes involved in claathrin-mediated vesicular transport from the Golgi or endosomes. Disruption of the pathway for display of HIV-1 antigens, which prevents recognition of the virus by cytotoxic T cells, has been shown to involve the AP-1 complex (PMID: 15569716). Alternative splicing results in multiple transcript variants.