An enhancer-blocking element between alpha and delta gene segments within the human T cell receptor alpha/delta locus

T cell receptor (TCR) alpha and delta gene segments are organized within a single genetic locus but are differentially regulated during T cell development. An enhancer-blocking element (BEAD-1, for blocking element alpha/delta 1) was localized to a 2.0-kb region 3' of TCR delta gene segments and 5' of TCR alpha joining gene segments within this locus. BEAD-1 blocked the ability of the TCR delta enhancer (E-delta) to activate a promoter when located between the two in a chromatin-integrated construct. We propose that BEAD-1 functions as a boundary that separates the TCR (alpha/delta locus into distinct regulatory domains controlled by E-delta and the TCR a enhancer, and that it prevents E-delta from opening the chromatin of the TCR alpha joining gene segments for VDJ recombination at an early stage of T cell development.