Role of Histone N-Terminal Tails and Their Acetylation in Nucleosome Dynamics

Abstract

Histone N-terminal tails are central to the processes that modulate nucleosome structure and function. We have studied the contribution of core histone tails to the structure of a single nucleosome and to a histone (H3-H4)₂ tetrameric particle assembled on a topologically constrained DNA minicircle. The effect of histone tail cleavage and histone tail acetylation on the structure of the nucleoprotein particle was investigated by analyzing the DNA topoisomer equilibrium after relaxation of DNA torsional stress by topoisomerase I. Removal of the H3 and H4 N-terminal tails, as well as their acetylation, provoked a dramatic change in the linking-number difference of the (H3-H4)₂ tetrameric particle, with a release of up to 70% of the negative supercoiling previously constrained by this structure. The (H3-H4)₂ tetramers containing tailless or hyperacetylated histones showed a striking preference for relaxed DNA over negatively supercoiled DNA. This argues in favor of a change in tetramer structure that constrains less DNA and adopts a relaxed flat conformation instead of its left-handed conformation within the nucleosome. In contrast neither removal or hyperacetylation of H3 and H4 tails nor removal or hyperacetylation of H2A and H2B N-terminal tails affected the nucleosome structure. This indicates that the globular domain of H2A and H2B is sufficient to stabilize the tailless or the hyperacetylated (H3-H4)₂tetramer in a left-handed superhelix conformation. These results suggest that the effect of histone tail acetylation that facilitates transcription may be mediated via transient formation of an (H3-H4)₂ tetrameric particle that could adopt an open structure only when H3 and/or H4 tails are hyperacetylated.

ACKNOWLEDGMENTS

We are grateful to A. Hamiche for his valuable contribution to the design of the experimental approach, to J. L. Baneres and J. Parello for their advice and help with histone tail cleavage by clostripain, to M. Grigoriev and D. Trouche for stimulating discussions, to K. D. Carr, M. Grigoriev, D. Trouche, and L. Vandel for critically reading the manuscript, and to C. Monod for linguistic corrections.

H.R.-F. has been awarded a grant from the Ligue Nationale Contre le Cancer as a member of an Equipe Labellisée La Ligue. This work was supported in part by the Association de la Recherche contre le Cancer, the GIP Fonds de Recherche HMR, and le Conseil de Région Midi-Pyrénées. V.M. is the recipient of a fellowship from the Ligue Nationale Contre le Cancer.