This proposal is focused on elucidating mechanisms which regulate expression of the T cell receptor beta chain gene. T-cell specific expression of an antigen receptor on the cell surface is essential for the two critical steps in T-cell ontogeny: 1) positive selection which determines the ability of T cells to recognize antigen in the context of the organism's own major histocompatibility antigens and 2) negative selection which ensures that T cells are tolerant to self-antigens. In mature T cells, occupation of the antigen receptor is required to activate T-cell proliferation and function. Thus, elucidating the molecular mechanisms which regulate beta chain gene expression is important not only for understanding a gene whose control is strictly T-cell and developmental stage specific, but also may guide understanding of immune deficiency and autoimmune diseases which result from T cell dysfunction. Our studies have shown that transcription of beta chain genes depends on a T-cell specific enhancer located 3' of C(B2) as well as on beta chain promoters. The activity of this enhancer is T cell specific and can be increased by treatment with phorbol esters, which mimics antigen activation of T cells. We will analyze the beta gene transcriptional enhancer in detail by mapping and verifying functionally all protein binding sites within it. We will focus particular attention on two enhancer proteins: those responsible for the T cell specific and antigen-responsive activity of the enhancer. We will clone cDNAs which encode these proteins and study their structure, function, interaction with other proteins and regulated expression. Our laboratory is also cloning and analyzing transcription factors which are important for immunoglobulin heavy chain gene expression. We feel that the T cell receptor beta enhancer studies will be synergistic with the ongoing immunoglobulin studies because similar theoretical and technical approaches will be used in both studies. Furthermore, since TCR and Ig genes are structurally, functionally and evolutionarily related, they are likely to share a subset of their regulatory mechanisms.