TEA (T early alpha) is a genetic element located upstream of the TCR-Jalpha cluster. Thymocytes from mice carrying a targeted deletion of TEA do not rearrange their TCRalpha locus on a window spanning the first nine Jalpha segments. This led us to the hypothesis of TEA having a "rearrangement focusing" activity on the 5' side of the TCR-Jalpha region. We analyzed DNAseI and "phylogenetic" footprints within the TEA promoter in an attempt to identify trans-acting factors that could account for its regulatory function on DNA accessibility. One of these footprints corresponded to a putative DNA-binding site for an orphan nuclear receptor of the ROR / RZR family. The RORgammaT cDNA clone was isolated from a thymus library using a probe corresponding to the DNA-binding domain of RORgamma / TOR. RORgammaT is a thymus-specific isoform of RORgamma, expressed almost exclusively in immature double-positive thymocytes. RORgammaT binds, to the TEA promoter in vitro. Lastly, the expression of RORgammaT is stimulated in two situations that mimic activation through the pre-TCR and in which the thymocytes have their TCR-alpha locus in an "open", yet unrearranged DNA configuration. We propose that the expression of RORgammaT may be part of the pre-TCR activation cascade leading to the maturation of alpha / beta T cells and may participate in the regulation of DNA accessibility in the TCR-Jalpha locus.