CDNA CLONING AND INTERFERON-GAMMA DOWN-REGULATION OF PROTEASOMAL SUBUNIT-X AND SUBUNIT-Y

Proteasomes are the proteolytic complex responsible for major histocom patibility complex (MHC) class I-restricted antigen presentation. Inte rferon gamma treatment increases expression of MHC-encoded LMP2 and LM P7 subunits of the proteasome and decreases expression of two proteaso me subunits, named X and Y, which alters the proteolytic specificity o f proteasomes. Molecular cloning of complementary DNAs encoding X and Y showed that their proteins are proteasomal subunits with high amino acid similarity to LMP7 and LMP2, respectively. Thus, interferon gamma may induce subunit replacements of X and Y by LMP7 and LMP2, respecti vely, producing proteasomes perhaps more appropriate for the immunolog ical processing of endogenous antigens.