The DRE motif is a key component in the expression regulation of the importin-β encoding Ketel gene in Drosophila

Importin-beta, encoded by the Ketel gene in Drosophila, is a key component of nuclear protein import, the formation of the spindle microtubules and the assembly of the nuclear envelope. The Drosophila embryos rely on the maternal importin-beta dowry at the beginning of their life. Expression of the zygotic Ketel gene commences during gastrulation in every cell and while the expression is maintained in the mitotically active diploid cells it ceases in the non-dividing larval cells in which nuclear protein import is assured by the long persisting importin-beta molecules. How is the expression of the Ketel gene regulated? In silico analysis revealed several conserved transcription factor binding sequences in the Ketel gene promoter. Reporter genes in which different segments of the promoter ensured transient expression of the luciferase gene in S2 cells identified the sequences required for normal Ketel gene expression level. Gel retardation and band shift assays revealed that the DREF and the CFDD transcription factors play key roles in the regulation of Ketel gene expression. Transgenic LacZ reporter genes revealed the sequences that ensure tissue-specific gene expression. Apparently, the regulation of Ketel gene expression depends largely on a DRE motif and action of the DREF, CFDD, CF2-II and BEAF transcription factors.