A DNA-BINDING PROTEIN IN HUMAN THYMOCYTES RECOGNIZES THE T-CELL RECEPTOR-DELTA-DELETING ELEMENT PSI-J-ALPHA

The TCR is a heterodimeric molecule composed of either gamma delta or alpha beta chains. The differentiation mechanisms that force thymocyte s into the gamma delta or alpha beta lineage are poorly understood, bu t rearrangement processes in the TCR-delta alpha locus are likely to p lay an important role. The TCR-S gene complex is flanked by the delta- deleting elements delta Rec and psi J alpha, which are assumed to dele te the TCR-delta gene before vary rearrangement. The nonproductive del ta Rec-psi J alpha recombination occurs at high frequency in both feta l and postnatal immature thymocytes. To find DNA binding proteins invo lved in the delta Rec-psi J alpha preferential rearrangement, we perfo rmed electrophoretic mobility shift assays using the recombination sig nal sequence of psi J alpha with additional upstream and downstream se quences. We observed a 180-kDa DNA binding protein in nuclear extracts from human thymocytes that recognized a 46-bp binding site on the psi J alpha gene segment, containing the core motif GTTAATAGG. This psi J alpha binding protein, which we call PJA-BP, was also detected in imm ature CD3(-) T cell lines with TCR-delta genes deleted on both alleles , in a TCR-alpha beta(+) cell line, and in two of four myeloid cell li nes. This protein was absent in a TCR-gamma delta+ T cell line, in non hemopoietic cell lines, and in all but one B cell lines tested, Althou gh we could detect binding activity of the PJA-BP to some other TCR-J alpha gene segments, we postulate that binding of PJA-BP to the psi J alpha gene segment is one of the factors involved in the preferential delta Rec-psi J alpha gene rearrangement process.