The long-term objective of this application is the definition at the molecular level of the RT1.E-grc region of the major histocompatibility complex (MHC) of the rat, and it continues the work performed during the preceding grant period. The specific aims are threefold. First, alloantisera and monoclonal antibodies will be raised against class I antigens encoded by this region using inbred, congenic and recombinant strains from our colony. They will be used primarily to identify the antigens encoded by genes in this region. Second, the physical mapping of the rat MHC by pulse field gel electrophoresis will be completed by linking the fragments of the central region that have already been identified and by a more detailed analysis of the class I regions. Third, the detailed molecular analysis of the RT1.grc region will build on pst work utilizing the genomic library generated from the R21 strain (Eu-grc+). Chromosome walking will be used to link the cosmid clones in this region. The class I genes isolated from this region will be sequenced; specific probes will be prepared for each of the genes; their developmental control will be determined; and their expression will be studied by northern analysis and by immunological identification of the expressed antigens. Since a critical part of our work is to identify and characterize genes in the grc region that affect development and susceptibility to cancer, the differences between the grc+ and grc- strains will be identified. Finally, transfection of unique grc+ sequences into grc- cell lines and the subsequent change in phenotype of these cell lines will be used to assess the biological activity of these sequences. The work described here is critical to exploring the central hypothesis of our laboratory: MHC-linked genes are evolutionarily important and have a central role in the control of growth and differentiation, the genesis of developmental abnormalities and susceptibility to cancer. This hypothesis is based on experimental evidence from the rat and from a number of other species and on extensive clinical evidence in humans. The experimental system in the rat will provide an unique approach to investigating these MHC-linked genes, which may include tumor suppressor gene. In addition, understanding the structure and function of the rat MHC is important for the study of comparative genetics and for the use of the rat as an experimental animal.