Abstract
It was confirmed that the flexible arm region of HUα forms an antiparallel β-sheet and that all of the residues of phenylalanines, together with some of leucines and/or valines, form a hydrophobic core within the dimer of HUα. HUα protein alone is thermally labile and melts at 38°C, but it becomes remarkably stabilized and melts at 59°C in the presence of DNA. Several resonances from both HUα and DNA perturbed by their complex formation, notably those of His C-2 and C-4 protons, downfield shifted Cα protons in the antiparallel β-sheet, as well as Arg Cδ and Lys Cε protons. The results indicated that a β-sheet region of HUα binds to DNA, and also showed that rapid equilibrium occurs on the NMR time scale between bound and unbound states of HUα. A few intermolecular nuclear Overhauser effects (NOEs) were also observed between the protein and H1' protons of DNA in the complex, suggesting that HUα binds primarily to the minor groove of DNA.
