AN ENHANCER-BLOCKING ELEMENT BETWEEN ALPHA-GENE AND DELTA-GENE SEGMENTS WITHIN THE HUMAN T-CELL RECEPTOR ALPHA DELTA LOCUS/

T cell receptor (TCR) alpha and delta gene segments are organized with in a single genetic locus but are differentially regulated during T ce ll development. An enhancer-blocking element (BEAD-1, for blocking ele ment alpha/delta 1) was localized to a 2.0-kb region 3' of TCR delta g ene segments and 5' of TCR alpha joining gene segments within this loc us. BEAD-1 blocked the ability of the TCR delta enhancer (E-delta) to activate a promoter when located between the two in a chromatin-integr ated construct. We propose that BEAD-1 functions as a boundary that se parates the TCR (alpha/delta locus into distinct regulatory domains co ntrolled by E-delta and the TCR a enhancer, and that it prevents E-del ta from opening the chromatin of the TCR alpha joining gene segments f or VDJ recombination at an early stage of T cell development.