the protein belongs to 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. p-gp is an atp-dependent drug efflux pump for xenobiotic compounds with broad substrate specificity. it is responsible for decreased drug accumulation in multidrug-resistant cells and often mediates the development of resistance to anticancer drugs. this protein also functions as a transporter in the blood–brain barrier. mutations in this gene are associated with colchicine resistance and inflammatory bowel disease 13. alternative splicing and the use of alternative promoters results in multiple transcript variants.