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.