This application requests renewal of support for the investigators studies of the """"""""non-classical"""""""" genes and gene products of the distal mouse major histocompatibility complex. Reflecting particularly important recent advances in their investigation of the maternally transmitted antigen (Mta), the proposal focuses specifically on work in that system. Mta is the cell surface product of three genes: the first, Hmt, is encoded on the 17th chromosome telomeric of TL and is thought to encode a class I heavy chain; the second, in keeping with the general structure of class I antigens, is beta2-microglobulin; the third, accounting for the maternally transmitted polymorphism of the cell surface antigen, is a mitochondrial gene that encodes a peptide, Mtf, corresponding to the N-terminus of the ND1 subunit of the mitochondrial respiratory enzyme NADH dehydrogenase. Mta is defined on the basis of target cell lysis by cytolytic T lymphocytes (CTL). The investigators' recent studies strongly suggest that the selectivity of the Mtf peptides for Hmt is a consequence of a specific binding pocket on Hmt for the N-formyl moiety characteristic of proteins translated on mitochondrial ribosomes (as well as proteins of prokaryotic origin). These workers hypothesize that the striking biochemical specificity of this class I molecule reflects its physiological functions. They will address five specific issues: 1) using synthetic N-formyl-peptides and appropriate analogs, they will define biochemical rules for Hmt-formyl-peptide interactions; 2) they will continue efforts to isolate and characterize the Hmt gene employing the strategy of retrovirus-mediated insertional mutagenesis; 3) they will develop a cell-free system and exploit a class I-inducible mutant cell line to assess physical and biochemical properties of the Hmt-formyl peptide complex independently of CTL-mediated cell lysis; 4) by subcellular fractionation and pulse-chase analysis, Dr. Rich and coworkers will investigate trafficking of Mtf peptides and cellular assembly of the Mta complex; and 5) they will examine the biological function(s) of Hmt, including the possibilities that it provides an intracellular mechanism for binding, transport and disposal of potential toxic formyl peptides and/or functions as an antigen-presenting molecule specialized for presentation of antigens of bacterial origin. These workers believe it likely that the proposed studies of the structure and specialized functions of Hmt will break new ground in the least understood region of the MHC and will provide fundamental knowledge of general importance in immunology and cell biology.
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