HOMONUCLEAR AND HETERONUCLEAR 2-DIMENSIONAL NMR-STUDIES OF THE GLOBULAR DOMAIN OF HISTONE H1 - FULL ASSIGNMENT, TERTIARY STRUCTURE, AND COMPARISON WITH THE GLOBULAR DOMAIN OF HISTONE H5

The globular domain of chicken histone H1 (GH1) has been studied by H-1 homonuclear and H-1-N-15 heteronuclear 2D NMR spectroscopy. After the full assignment of the proton and N-15 resonances, the tertiary structure of GH1 was determined by an iterative procedure using distance geometry and restrained simulated annealing. The secondary structure elements of GH1, three helices (S5-A16, S24-A34, N42-K56) followed by a beta-hairpin (L59-L73), are folded in a manner very similar to the corresponding parts of the globular domain of chicken histone H5 (GH5) [Clore et al. (1987) EMBO J. 6, 1833-1842; Ramakrishnan et al. (1993) Nature 362, 219-223]. However, subtle differences are detected between the two structures and between the electrostatic potentials surrounding the molecules. The most important differences are located in the loop between the second and third helices, a region that could be responsible for the different affinity for DNA. The most positively charged regions are not found in exactly the same position in GH1 and GH5. Nevertheless, their location seems to agree with the model where nucleosome binding takes place through contact points located at one DNA terminus and close to the dyad axis of the nucleosome [Schwabe & Travers (1993) Curr. Biol. 3, 628-630].