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 m onomer, through interactions with the DNA backbone and through both di rect and water-mediated major and minor groove base contacts, inducing a 13-degrees bend. The transcription factor fold is very similar to t he structure of histone H5. In its amino-terminal half, three alpha-he lices adopt a compact structure that presents the third helix to the m ajor groove. The remainder of the protein includes a twisted, antipara llel beta-structure and random coil that interacts with the minor groo ve.