A 36-Kilodalton Cellular Transcription Factor Mediates an Indirect Interaction of Human T-Cell Leukemia/Lymphoma Virus Type I TAX₁ with a Responsive Element in the Viral Long Terminal Repeat

Abstract

The human T-cell leukemia/lymphoma virus type I (HTLV-I) trans activator, TAX₁, interacts indirectly with a TAX₁-responsive element, TRE-2, located at positions −117 to −163 in the viral long terminal repeat. This report describes the characterization of a 36-kilodalton (kDa) protein identified in HeLa nuclear extract which mediates the interaction of TAX₁ with TRE-2. Purification of the protein was achieved by zinc chelate chromatography and preparative sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The renatured 36-kDa protein bound specifically to a TRE-2 oligonucleotide but not to nonfunctional base substitution mutant probes in a gel retardation assay. Renatured proteins of differing molecular weights were unable to form this complex. In addition, the 36-kDa protein specifically activated transcription from the HTLV-I promoter in vitro. Purified TAX₁ protein formed a complex with the TRE-2 oligonucleotide in the presence of the 36-kDa protein, suggesting that indirect interaction of TAX₁ with the viral long terminal repeat may be one of the mechanisms by which HTLV-I transcription is regulated. ^{* †}