The 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 White subfamily.The protein encoded by this gene functions as a half-transporter to limit intestinal absorption and promote biliary excretion of sterols.It is expressed in a tissue-specific manner in the liver, colon, and intestine.This gene is tandemly arrayed on chromosome 2, in a head-to-head orientation with family member ABCG8.Mutations in this gene may contribute to sterol accumulation and atheroschlerosis, and have been observed in patients with sitosterolemia.