Beta2-microglobulin is a small polypeptide found on the surface of virtually all mammalian cells in close, but non-covalent association with a variety of glycoproteins encoded within the major histocompatibility complex (MHC). These include the classical transplantation antigens, H-2 or HLA, and the differentiation antigens, TL, Qa-1 and Qa-2. Although the functions of beta2-microglobulin are not well defined, it appears to be required for surface expression of the MHC antigens, which are in turn important in the killing of virally infected cells, graft rejection and other cellular interations and the control of expression of both chains of the MHC antigens to fully define their role in such immune functions and to provide the ability to manipulate immune responses by altering gene expression. We have previously cloned the mouse gene encoding beta2-microglobulin and will now study the mechanism of regulation of its expression. We will characterize the promoter region both structurally and functionally using in vitro and in vivo transcriptional assays. We will examine the relationship between alterations in chromatin structure and the expression of the gene by analyzing changes in DNAase I hypersensitive sites and methylation when the gene is transcriptionally active (differentiated cells) versus inactive (teratocarcinoma stem cells). We will use DNA-mediated gene transfer into mutant lines both to prove that a functional beta2-micro globulin gene is required for surface expression of H-2 and TL antigens, and to determine the parts of the protein required for association, transport to the cell surface, and cellular recognition of these MHC antigens. We will investigate the relationship between a highly repetitive element within the body of the beta2-microglobulin gene and a closely situated "hot spot" for mutation. Finally, we will study the evolutionary history of these gene, which appears to have evolved from the same common ancestor as the genes encoding immunoglobulin and H-2 domains.