The generation of antigenic peptides and their transport across the membran
e of the endoplasmic reticulum for assembly with MHC class 1 molecules are
essential steps in antigen presentation to cytotoxic T lymphocytes. Recent
studies have characterized the substrate specificities of the proteasome an
d. the transporter associated with antigen processing. It is interesting to
compare the specificity of this transporter to the wide spectrum of peptid
es generated by the proteasome, to the binding motifs of MHC class 1 molecu
les and in particular to the principles of T cell recognition.