TAP1, is a member of the ATP-binding cassette (ABC) family of transmembrane transporters and is an essential component of the major histocompatability complex (MHC) class I antigen-presenting pathway. TAP is involved in the transport of antigens from the cytoplasm to the endoplasmic reticulum for association with MHC class I molecules. It also acts as a molecular scaffold for the final stage of MHC class I folding. Defects in TAP1 are a cause of bare lymphocyte syndrome type 1 (BLS1).
