GENERATION OF NATURALLY PROCESSED PEPTIDE MHC CLASS-I COMPLEXES IS INDEPENDENT OF THE STABILITY OF ENDOGENOUSLY/SYNTHESIZED PRECURSORS/

Proteolysis of endogenously synthesized cellular proteins is essential far constitutive display of processed peptide/MHC class I complexes o n the APC surface for stimulating CD8(+) T cells. However, the extent to which normal protein turnover serves as the source of processed pep tides is not clear. To address this question, rye used pairs of novel N-end rule substrates that varied in their intracellular stability and served as precursors for generating peptide/MHC class I (OVA257-264/K -b or influenza nucleoprotein 366-374/D-b) complexes. Surprisingly, al though each oi three precursor pairs tested varied profoundly in their intracellular stability, they were indistinguishable in either T cell stimulation assays, or in the amounts of naturally processed peptides in the APC extract. Our findings demonstrate that the proteolytic tur nover of endogenously synthesized proteins is not directly proportiona l to the generation of processed antigenic peptide/MHC class I complex es.