The TATA box binding protein (TBP) is a general transcription factor required for initiation by all three eukaryotic RNA polymerases. Previously, we found that the promoter region of the Drosophila melanogaster TBP gene contains three sequences similar to the DNA replication-related element (DRE) (5P P-TATCGATA). In the present study, we found that the DRElike sequences are also present in the promoter of the Drosophila virilis TBP gene, suggesting a role for these sequences in TBP expression. Band mobility shift assays revealed that oligonucleotides containing sequences similar to the DRE of D. melanogaster TBP gene promoter form specific complexes with a factor in a Kc cell nuclear extract and with recombinant DRE-binding factor (DREF). Furthermore, these complexes were either supershifted or diminished by monoclonal antibodies to DREF. Transient luciferase assays demonstrated that induction of mutations in two DRE-related sequences at positions 3 3223 and 3 363 resulted in an extensive reduction of promoter activity. Thus, the DRE^DREF system appears to be involved in the expression of the D. melanogaster TBP gene. ß

DREF [DRE (DNA replication-related element) binding factor] is an 80 kDa polypeptide homodimer which plays an important role in regulating cell proliferation-related genes. Both DNA binding and dimer formation activities are associated with residues 16-115 of the N-terminal region. However, the mechanisms by which DREF dimerization and DNA binding are regulated remain unknown. Here, we report that the DNA binding activity of DREF is regulated by a redox mechanism, and that the cysteine residues are involved in this regulation. Electrophoretic mobility shift analysis using Drosophila Kc cell extracts or recombinant DREF proteins indicated that the DNA binding domain is sufficient for redox regulation. Site-directed mutagenesis and transient transfection assays showed that Cys59 and/or Cys62 are critical both for DNA binding and for redox regulation, whereas Cys91 is dispensable. In addition, experiments using Kc cells indicated that the DNA binding activity and function of DREF are affected by the intracellular redox state. These findings give insight into the exact nature of DREF function in the regulation of target genes by the intracellular redox state.