SEQUENCE-SPECIFIC BINDING OF HUMAN ETS-1 TO THE T-CELL RECEPTOR ALPHA-GENE ENHANCER

Expression of the human T cell receptor (TCR) α gene is regulated by a T cell - specific transcriptional enhancer that is located 4.5 kilobases (kb) 3′ to the Cα gene segment. The core enhancer contains two nuclear protein binding sites, Tα1 and Tα2, which are essential for full enhancer activity. Tα1 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 Tα2 site have not been defined. In this report, a γgt11 expression protocol was used to isolate a complementary DNA (cDNA) that programs the expression of a Tα2 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 β-galactosidase - Ets-1 fusion protein that bound specifically to a synthetic Tα2 oligonucleotide. The Ets-1 binding site was localized to a 17 - base pair (bp) region from the 3′ end of Tα2. Mutation of five nucleotides within this sequence abolished both Ets-1 binding and the activity of the TCR α enhancer in T cells. These results demonstrate that Ets-1 binds in a sequence-specific fashion to the human TCR α enhancer and suggest that this developmentally regulated proto-oncogene functions in regulating TCR α gene expression.