Chromatin Higher Order Structure and Regulation of its Compaction

Abstract

During the past decade it has become evident that histone post-translational modifications are key regulators of nuclear processes whose substrate is DNA. Whilst the effects of, for instance, histone post-translational modification on transcription are well-documented, there is no mechanistic understanding of how such modification regulate chromatin condensation directly, or indirectly. Such an understanding is dependent on knowledge of the three-dimensional structure of chromatin. Although the structure of the first level of DNA folding, the nucleosome core, is known at atomic resolution, the structure of the second level of folding, whereby a string of nucleosomes folds into a fibre with an approximate diameter of 30 nm remains undetermined. I will describe our studies on the higher orders structure of chromatin with two primary aims:1) Determination of “30nm” chromatin fibre structure to provide an understanding of fibre topology.2) Biophysical characterization of the effects of the linker histone and histone modifications on the compaction of chromatin higher order structure.EM measurements define the dimensions of the “30nm” chromatin fiber: Evidence for a compact, interdigitated structureRobinson, J. J. P., Fairall, L., Huynh, V. A. T. and Rhodes, D.(2006) Proc. Natl. Acad. Sci. USA 103, 6506-1130 nm chromatin fibre decompaction requires both H4-K16 acetylation and linker histone evictionRobinson PJ, An W, Routh A, Martino F, Chapman L, Roeder RG and Rhodes D.(2008) J. Mol. Biol. 381: 816-25Nucleosome repeat length and linker histone stoichiometry determine chromatin fiber structureRouth A, Sandin S and Rhodes D.(2008) Proc. Natl. Acad. Sci. U S A. 105: 8872-7Single-molecule force spectroscopy reveals a highly compliant helical folding for the 30-nm chromatin fiberKruithof M, Chien FT, Routh A, Logie C, Rhodes D, van Noort J.(2009) Nat. Struct. Mol. Biol.16:534-40