Expression of the human T cell receptor (TCR) alpha gene is regulated by a T cell-specific transcriptional enhancer that is located 4.5 kilobases (kb) 3' to the C alpha gene segment. The core enhancer contains two nuclear protein binding sites, T alpha 1 and T alpha 2, which are essential for full enhancer activity. T alpha 1 contains a consensus cyclic adenosine monophosphate (cAMP) response element (CRE) and binds a set of ubiquitously expressed CRE binding proteins. In contrast, the transcription factors that interact with the T alpha 2 site have not been defined. In this report, a lambda gt11 expression protocol was used to isolate a complementary DNA (cDNA) that programs the expression of a T alpha 2 binding protein. DNA sequence analysis demonstrated that this clone encodes the human ets-1 proto-oncogene. Lysogen extracts produced with this cDNA clone contained a beta-galactosidase-Ets-1 fusion protein that bound specifically to a synthetic T alpha 2 oligonucleotide. The Ets-1 binding site was localized to a 17-base pair (bp) region from the 3' end of T alpha 2. Mutation of five nucleotides within this sequence abolished both Ets-1 binding and the activity of the TCR alpha enhancer in T cells. These results demonstrate that Ets-1 binds in a sequence-specific fashion to the human TCR alpha enhancer and suggest that this developmentally regulated proto-oncogene functions in regulating TCR alpha gene expression.

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