Transcriptional regulation of the Drosophila-raf proto-oncogene by the DNA replication-related element (DRE)/DRE-binding factor (DREF) system

The DRE/DREF system plays an important role in transcription of DNA replication genes such as those encoding the 180 and 73 kDa subunits of DNA polymerase α as well as that for encoding PCNA. In this study, we found two sequences homologous to DRE (5′-TATCGATA-3′) in the 5′-flanking region (−370 to −357 with respect to the transcription initiation site) of the D-raf gene and confirmed transcriptional activity through gel mobility shift assays, transient CAT assays, and spatial patterns of lacZ expression in transgenic larval tissues carrying D-raf and lacZ fusion genes. Further, we demonstrated that the D-raf gene is another target of the Zerknüllt (Zen) protein with observation of D-raf repression by Zen protein in cultured cells and its ectopic expression in the dorsal region of the homozygous zen mutant embryo. The evidence of DRE/DREF involvement in regulation of the D-raf gene obtained in this study strongly supports the idea that the DRE/DREF system is responsible for the coordinated regulation of cell proliferation-related genes in Drosophila.