Indistinguishable nuclear factor binding to functional core sites of the T-cell receptor delta and murine leukemia virus enhancers.

We have previously shown that the delta E3 site is an essential element for transcriptional activation by the human T-cell receptor (TCR) delta enhancer and identified two factors, NF-delta E3A and NF-delta E3C, that bound to overlapping core (TGTGGTTT) and E-box motifs within delta E3. In this study, we show that protein binding to the core motif is necessary but not sufficient for transcriptional activation by the delta E3 element. In contrast, protein binding to the E-box motif does not contribute significantly to enhancer activity. A similar core motif present within the enhancers of T-cell-tropic murine retroviruses has been shown to contribute to transcriptional activity of the viral long terminal repeat in T lymphocytes and to viral T-cell tropism. We therefore determined the relationship between the nuclear factors that bind to the TCR delta and Moloney murine leukemia virus core motifs. On the basis of electrophoretic mobility shift binding and competition studies, biochemical analysis of affinity-labeled DNA-binding proteins, and the binding of a purified core binding factor, the proteins that bound to the TCR delta core site were indistinguishable from those that bound to the murine leukemia virus core site. These data argue that DNA-binding proteins that interact with the core site of murine leukemia virus long terminal repeats and contribute to viral T-cell tropism also play an essential role in the T-cell-specific expression of cellular genes.