Enhancer § -dependent histone acetylation has been proposed as a molecular mechanism underlying the control of accessibility of recombination signal sequences along the TCR § locus. Here we show that chromatin acetylation along the first J § segments is under the dependence of the T early § element (TEA), located upstream of TCRJ § locus. The targeted deletion of TEA leads to an absence of histones H3 and H4 tail acetylation, while maintaining histone acetylation in the region spanning downstream J § segments. During thymocyte maturation, TEA-dependent histone acetylation appears at immature single-positive stage, known to represent the stage of V § J § initiation. TEA-dependent histone acetylation of the most upstream J § segments leads to enhanced DNA accessibility thus optimizing TCRJ § usage and increasing Ag receptor diversity potential.