INTERACTION OF MHC CLASS-I MOLECULES WITH THE TRANSPORTER ASSOCIATED WITH ANTIGEN-PROCESSING

The transporter associated with antigen processing (TAP) delivers cyto solic peptides into the endoplasmic reticulum (ER) where they bind to nascent class I histocompatibility molecules. Class I-peptide complexe s are then displayed at the cell surface for recognition by cytotoxic T lymphocytes. Immunoprecipitation of either TAP or class I molecules revealed an association between the transporter and diverse class I pr oducts. TAP bound preferentially to heterodimers of the class I heavy chain and beta(2)-microglobulin, and the complex subsequently dissocia ted in parallel with transport of class I molecules from the ER to the Golgi apparatus. The TAP-class I complexes could also be dissociated in vitro by the addition of class I-binding peptides. The association of class I molecules with TAP likely promotes efficient capture of pep tides before their exposure to the lumen of the ER.