This gene encodes the sigma subunit of the heterotetrameric adaptor protein complex AP-3 which is involved in the formation of specialized lysosome-related compartments such as melanosomes. Alternate splicing of this gene results in multiple transcript variants encoding different isoforms. Pseudogenes of this gene are found on chromosomes 1, 8, 16, 17 and X. [provided by RefSeq, Dec 2014]