CO-CRYSTAL STRUCTURE OF THE HNF-3/FORK HEAD DNA-RECOGNITION MOTIF RESEMBLES HISTONE-H5

The three-dimensional structure of an HNF-3/fork head DNA-recognition motif complexed with DNA has been determined by X-ray crystallography at 2.5 angstrom resolution. This alpha/beta protein binds B-DNA as a monomer, through interactions with the DNA backbone and through both direct and water-mediated major and minor groove base contacts, inducing a 13-degrees bend. The transcription factor fold is very similar to the structure of histone H5. In its amino-terminal half, three alpha-helices adopt a compact structure that presents the third helix to the major groove. The remainder of the protein includes a twisted, antiparallel beta-structure and random coil that interacts with the minor groove.