Cloning, expression, and characterization of the TATA-binding protein (TBP) promoter binding factor, a transcription activator of the Acanthamoeba TBP gene.

TATA-binding protein (TBP) gene promoter binding factor (TPBF) is a transactivator which binds to the TBP promoter element (TPE) sequence of the Acanthamoeba TBP gene promoter and stimulates transcription in vitro. We have isolated a cDNA clone encoding TPBF. TPBF is a polypeptide of 327 amino acids with a calculated molecular mass of 37 kDa. The predicted amino acid sequence of TPBF shows no significant homology to other proteins. TPBF has two potential coiled-coil regions, a basic region, a proline-rich region, a histidine-rich N terminus, and a nuclear targeting sequence. The recombinant protein has an apparent molecular mass of 50 kDa, identical with that of TPBF purified from Acanthamoeba. Recombinant TPBF is able to bind DNA and activate transcription with the same specificity as natural Acanthamoeba TPBF, demonstrating the authenticity of the clone. Mobility shift assays of co-translated TPBF polypeptides and chemical cross-linking demonstrate that TPBF is tetrameric in solution and when bound to DNA. Analyses of TPBF mutants show that Coiled-coil II is essential for DNA binding, but Coiled-coil I and the basic region are also involved. TPBF is thus a novel DNA-binding protein with functional similarity to the tumor suppressor protein p53.