BINDING-SITES FOR TRANSCRIPTION FACTOR NTF-1 ELF-1 CONTRIBUTE TO THE VENTRAL REPRESSION OF DECAPENTAPLEGIC/

The Dorsal morphogen is a transcription factor that activates some gen es and represses others to establish multiple domains of gene expressi on along the dorsal/ventral axis of the early Drosophila embryo. Repre ssion by Dorsal appears to require accessory proteins that bind to cor epression elements in Dorsal-dependent regulatory modules called ventr al repression regions (VRRs). We have identified a corepression elemen t in decapentaplegic (dpp), a zygotically active gene that is represse d by the Dorsal morphogen. This dpp repression element (DRE) is locate d within a previously identified VRR and close to essential Dorsal-bin ding sites. We have purified a factor from Drosophila embryo extracts that binds to the DRE but not to mutant forms of the DRE that fail to support efficient repression. This protein also binds to an apparently essential region in a VRR associated with the zerknullt (zen) gene. O ne of the DREs in the dpp VRR overlaps the binding site for a potentia l activator protein suggesting that one mechanism of ventral repressio n may be the mutually exclusive binding of repressor and activator pro teins. We have found the DRE-binding protein to be identical to NTF-1 (equivalent to Elf-1, the product of the grainyhead gene), a factor or iginally identified as an activator of the Ultrabithorax and Dopa deca rboxylase promoters. NTF-1 mRNA is synthesized during oogenesis and de posited in the developing oocyte where it is available to contribute t o ventral repression during early embryogenesis. Previous studies have shown that overexpression of NTF-1 in the postblastoderm embryo resul ts in a phenotype that is consistent with a role for this factor in th e repression of dpp later in embryogenesis.