wingless and decapentaplegic signal during endoderm induction in Drosophila to regulate expression of the homeotic gene Ultrabithorax. Here, we define a minimal wingless response sequence in the midgut enhancer of Ultrabithorax. We show that this sequence is recognized by the murine transcription factor LEF-1 (lymphocyte enhancer binding factor 1) in a ternary complex with armadillo protein, the cytoplasmic target of the wingless signaling pathway. In stable transformants, transcriptional stimulation of the Ultrabithorax enhancer by LEF-1 depends on armadillo. Furthermore, overexpression of LEF-1 bypasses the need for wingless signaling and causes phenotypes in the midgut, notum, and wing that mimic wingless hyperstimulation. Finally, efficient transcriptional stimulation by LEF-1 in the midgut depends also on the decapentaplegic response sequence and is limited spatially by decapentaplegic signaling. Thus, LEF-1 coordinates inputs from multiple positional signals, consistent with its architectural role in regulating the assembly of multiprotein enhancer complexes.

LEF-1 is a transcription factor that participates in the regulation

The polyomavirus enhancer binding protein 2K K (PEBP2K K) is a DNA binding transcriptional regulatory protein that binds conserved sites in the polyomavirus enhancer, mammalian type C retroviral enhancers and T-cell receptor gene enhancers. Binding of PEBP2K K and homologous proteins to the consensus DNA sequence TGPyGGTPy is mediated through a protein domain known as the runt domain. Although recent NMR studies of DNA-bound forms of the runt domain have shown an immunoglobulin-like (Ig) fold, the identification of residues of the protein that are involved in DNA binding has been obscured by the low solubility of the runt domain. Constructs of the mouse PEBP2K KA1 gene were generated with N-and Cterminal extensions beyond the runt homology region. The construct containing residues Asp90 to Lys225 of the sequence (PEBP2K K90^225) yielded soluble protein. The residues that participate in DNA binding were determined by comparing the NMR spectra of free and DNA-bound PEBP2K K90^225. Analysis of the changes in the NMR spectra of the two forms of the protein by chemical shift deviation mapping allowed the unambiguous determination of the regions that are responsible for specific DNA recognition by PEBP2K K. Five regions in PEBP2K K90^225 that are localized at one end of the L L-barrel were found to interact with DNA, similar to the DNA binding interactions of other Ig fold proteins.z 2000 Federation of European Biochemical Societies.

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