Targeted expression of the DNA binding domain of DRE-binding factor, a Drosophila transcription factor, attenuates DNA replication of the salivary gland and eye imaginal disc

The promoters of Drosophila genes encoding DNA replication-related proteins contain transcription regulatory elements consisting of an 8-bp palindromi c DNA replication-related element (DRE) sequence (5'-TAT CGATA). The specif ic DRE-binding factor (DREF), a homodimer of the polypeptide with 709 amino acid residues, is a positive trans-acting factor for transcription of DRE- containing genes. Both DRE binding and dimer formation are associated with residues 16 to 115 of the N-terminal region. We have established transgenic flies expressing the full-length DREF polypeptide or its N-terminal fragme nt (amino acid residues 1 to 125) under the control of the heat shock promo ter, the salivary gland-specific promoter, or the eye imaginal disc-specifi c promoter. Heat shock induction of the N-terminal fragment during embryoni c, larval, or pupal stages caused greater than 50% lethality. This lethalit y was overcome by coexpression of the full length DREF. In salivary glands of the transgenic larvae expressing the N-terminal fragment, this fragment formed a homodimer and a heterodimer with the endogenous DREF. Ectopic expr ession of the N-terminal fragment in salivary gland cells reduced the conte nts of mRNAs for the 180-kDa subunit of DNA polymerase alpha and for dE2F a nd the extent of DNA endoreplication. Ectopic expression of the N-terminal fragment in the eye Imaginal discs significantly reduced DNA replication in cells at the second mitotic wave. The lines of evidence suggest that the N -terminal fragment can impede the endogenous DREF function in a dominant ne gative manner and that DREF is required for normal DNA replication in both mitotic cell cycle and endo cycle.