Multiple nuclear proteins bind upstream sequences in the promoter region of a T-cell receptor β-chain variable-region gene: Evidence for tissue specificity

Abstract

DNA-nuclear protein binding interactions were examined in the promoter region of a representative T-cell receptor Ti β-chain variable-region gene by means of electrophoretic mobility-shift and DNase I-protection analysis. Within 175 bases upstream of the transcription initiation site, four protected regions ('footprints') were identified on the coding strand, at nucleotides -46 to -68 (I), -72 to -92 (II), -113 to -134 (III), and -136 to -175 (IV). Nuclear proteins (0.6 M NaCl fraction from a heparin-Sepharose column chromatography of nuclear extracts) of a variety of cell types produced footprints I, III, and IV and a fifth footprint (beyond nucleotide -200). In contrast, footprint II was produced only by T-cell extracts, although nuclear extracts of a transformed B-lymphoblastoid line produced a partial footprint in this region. Furthermore, footprint analysis of the noncoding strand showed that a continuous region of protection corresponding to the entire region of footprints I and II was generated, along with a DNase I-hypersensitive site, by nuclear proteins derived from T cells but not other cell types. Footprint I has the sequence structure of many well-defined protein-DNA binding sites. Nucleotide sequences in the region of footprint II bore no homology to known sequences, whereas those in the areas of footprints III and IV were similar to motifs within immunoglobulin and other enhancers. These findings may have implications for the tissue specificity of human Ti β-chain gene transcription.