The membrane-associated protein encoded by this gene is a member of the superfamily of ATP-binding cassette (ABC) transporters. ABC proteins transport various molecules across extra- and intra-cellular membranes. ABC genes are divided into seven distinct subfamilies (ABC1, MDR/TAP, MRP, ALD, OABP, GCN20, White). This protein is a member of the MDR/TAP subfamily. Members of the MDR/TAP subfamily are involved in multidrug resistance. The protein encoded by this gene is involved in antigen presentation. This protein forms a heterodimer with Tap1 in order to transport peptides from the cytoplasm to the endoplasmic reticulum. Mutations in the human gene may be associated with ankylosing spondylitis, insulin-dependent diabetes mellitus, and celiac disease. [provided by RefSeq, Jul 2008]