The role of viral enhancer "core" motif-related sequences in regulating T cell receptor-gamma and -delta gene expression.

T cells express clonally distributed alpha beta or gamma delta Ag receptor heterodimers. Transcriptional enhancers for the genes of all four subunits are active in both gamma delta and alpha beta T cells, but are less active or inactive in other cells. Conserved sequence motifs are present in all four enhancers, suggesting that common transcription factors regulate TCR gene expression. One of these motifs in the gamma 3 site of the TCR-gamma enhancer is similar to motifs found in several other lymphoid-specific and viral enhancers. This conserved "core" sequence is present in the enhancers of Moloney and SL3-3 murine leukemia viruses, important for transcription in T cells and in determining disease specificity. Here we characterize the gamma 3 site of the gamma enhancer and a corresponding homologous site, delta E3, of the TCR-delta enhancer. Our results suggest that the core site is critical for activity of the 200-bp gamma enhancer fragment and of the gamma 3 and delta E3 sites. Furthermore, we identify a nuclear factor in human T cell lines that specifically binds the core region in these and several other core-containing enhancers. This factor may be identical to or related to a purified bovine nuclear core binding factor that binds the core region of the Moloney murine leukemia virus enhancer, gamma 3 and delta E3 sites, suggesting that similar proteins regulate the TCR-gamma, delta and Moloney murine leukemia virus enhancers. Other sequences in the gamma 3 site upstream of the core sequence are also critical for activity in T cells, suggesting that at least two different factors are required for functional activity of the gamma 3 site.