ANALYSES OF THE TRANSCRIPTIONAL REGULATORY NETWORK FOR DROSOPHILA DNA REPLICATION GENES

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We have identified a novel transcriptional regulatory element, PRE (positive regulatory element) located between URE (upstream regulatory element) and DRE (DNA replication-related element) in the Drosophila PCNA (proliferating cell nuclear antigen) gene. One-hybrid screening using the PRE sequence as a bait allowed us to clone a CDNA encoding a novel transcription factor carrying the RFX domain. The factor was named as Drfx2 (Drosophila RFX2). Over expression of DNA-binding domain of this factor induced the abnormal eye morphology (rough eye phenotype) hi adult flies. Since the human RFX protein is reported to be involved in regulation of the human PCNA gene, function of RFX family protein may be conserved between mammal and Drosophila.We have also identified Mi-2, a chromatin remodeling factor as an interactant of the transcription factor DREF that coordinately regulates DNA replication related genes in Drosophila. Over-expression of DREF in eye imaginal discs induces ectopic DNA synthesis and apoptosis in eye disc cells and consequently the adult flies exhibit the rough eye phenotype. Half reduction of the Mi-2 gene dose strongly enhanced the DREFinduced rough eye phenotype, suggesting that Mi-2 negatively regulates the function of DREF in vivo. In consistent with this, the purified GST-Mi-2 fusion protein inhibits DNA-binding activity of DREF in vitro.