This gene encodes a transmembrane glycoprotein which
mediates interaction between newly assembled major
histocompatibility complex (MHC) class I molecules and the
transporter associated with antigen processing (TAP), which is
required for the transport of antigenic peptides across the
endoplasmic reticulum membrane. This interaction is essential for
optimal peptide loading on the MHC class I molecule. Up to four
complexes of MHC class I and this protein may be bound to a single
TAP molecule. This protein contains a C-terminal double-lysine
motif (KKKAE) known to maintain membrane proteins in the
endoplasmic reticulum. This gene lies within the major
histocompatibility complex on chromosome 6. Alternative splicing
results in three transcript variants encoding different isoforms.
