Characterization of human TCR Vbeta gene promoter. Role of the dodecamer motif in promoter activity.

During T-lymphocyte development, the T-cell antigen receptor (TCR) gene expression is controlled by its promoter and enhancer elements and regulated in tissue- and development stage-specific manner. To uncover the promoter function and to define positive and negative regulatory elements in TCR gene promoters, the promoter activities from 13 human TCR Vbeta genes were determined by the transient transfection system and luciferase reporter assay. Although most of the TCR Vbeta gene promoters that we tested are inactive by themselves, some promoters were found to be constitutively strong. Among them, Vbeta6.7 is the strongest. 5'-Deletion and fragmentation experiments have narrowed the full promoter activity of Vbeta6.7 to a fragment of 147 base pairs immediately 5' to the transcription initiation site. A decanucleotide motif with the consensus sequence AGTGAYRTCA has been found to be conserved in most TCR Vbeta gene promoters. There are three such decamer motifs in the promoter region of Vbeta6.7, and the contribution of each such motif to the promoter activity has been examined. Further site-directed mutagenesis analyses showed that: 1) when two Ts in the decamer were mutated, the promoter activity was totally abolished; 2) when two additional nucleotides 3' to the end of decamer were mutated, the promoter activity was decreased to two-thirds of the full level; and 3) when the element with the sequence AGTGATGTCACT was inserted into other promoters, the original weak promoters become very strong. Taken together, our data suggest that the positive regulatory element in Vbeta6.7 should be considered a dodecamer rather than a decamer and that it confers strong basal transcriptional activity on TCR Vbeta genes.