The membrane-associated protein encoded by this gene is included in 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 White subfamily. Alternatively referred to as a breast cancer resistance protein, the human protein functions as a xenobiotic transporter which may play a major role in multi-drug resistance. This protein likely serves as a cellular defense mechanism in response to mitoxantrone and anthracycline exposure. [provided by RefSeq, Jul 2008]