A heterodimer composed of the subunits TAP1 and TAP2 (transporter associated with antigen presentation). Functions in the transport of antigenic peptides from the cytosol to the lumen of the endoplasmic reticulum. [ http://www.ncbi.nlm.nih.gov/pubmed/10618487 http://www.ncbi.nlm.nih.gov/pubmed/10631934 ]