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 th e full assignment of the proton and N-15 resonances, the tertiary stru cture of GH1 was determined by an iterative procedure using distance g eometry and restrained simulated annealing. The secondary structure el ements 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 cor responding parts of the globular domain of chicken histone H5 (GH5) [C lore et al. (1987) EMBO J. 6, 1833-1842; Ramakrishnan et al. (1993) Na ture 362, 219-223]. However, subtle differences are detected between t he 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 responsi ble for the different affinity for DNA. The most positively charged re gions are not found in exactly the same position in GH1 and GH5. Never theless, their location seems to agree with the model where nucleosome binding takes place through contact points located at one DNA terminu s and close to the dyad axis of the nucleosome [Schwabe & Travers (199 3) Curr. Biol. 3, 628-630].