Identification of a Functional Nf-kb Binding Site in the Murine T Cell Receptor 02 Locus

The cr and /3 chains constituting the TCR are expressed specifically on T lymphoid cells after genomic rearrangements have led to the assembly of functional a and /3 chain genes (1) . T cell-specific transcriptional activation of the unrearranged gene segments is considered to be a prerequisite for the recombination process that apparently uses the same enzymatic machinery that rearranges the Ig genes in B lymphocytes (2). Identification of cu-acting DNA regulatory sequences that govern transcription ofthese loci is therefore likely to be important not only for understanding gene expression in mature Tcells but also early events during T cell development (3, 4). Analysis of mice transgenic for a rearranged TCR 0 chain gene has led to the identification of an enhancer element located 3' of the exons encoding the constant region (C(3) of this gene (5). Transient transfections into lymphoid andnonlymphoid cells have allowed its localization to a 550-bp DNA fragment N5 kb downstream of the Cat exon (6, 7) . Although the existence of another regulatory sequence in the TCRa gene has been suggested by the identification of T cell-specific DNAase 1 hypersensitive sites (8, 9) in the major intron of the murine /32 gene, experiments to functionally define such an element have been unsuccessful thus far (7). We have investigated the interaction of nuclear proteins with DNA fragments derived from this region ofthe C(3 locus. We report here the identification of a sequence element in the J02-CO2 intron that is homologous to the KB element (10) of the Ig K light chain gene enhancer. We demonstrate by transfection analysis into B and T lymphoid cell lines that this sequence can serve as an inducible T cell-specific regulatory element and thereby provide evidence for the presence of transcription regulatory sequences located within the TCR Jag-CO2 intron .