Major histocompatibility complex (MHC) class 1 molecules bind to antigens for presentation on the surface of cells. The proteasome is responsible for producing these antigens from the components of foreign pathogens. MHC class 1 molecules consist of an a heavy chain that contains three subdomains ((alpha)1, (alpha)2, (alpha)3), and a non-covalent associating light chain, known as (beta)-2-Microglobulin. (beta)-2-Microglobulin associates with the a3 subdomain of the a heavy chain and forms an immunoglobulin domain-like structure that mediates proper folding and expression of MHC class 1 molecules. The (alpha)1 and (alpha)2 domains of the a heavy chain form the peptide antigen-binding cleft. Mice that lack (beta)-2-Microglobulin protein show a normal distribution of T cells, yet have no mature CD4-8+ T cells and are defective in CD4-8+ T cell-mediated cytotoxicity. Interferon-(gamma) can stimulate production of (beta)-2-Microglobulin transcripts.