title: Dynamics of nucleosome assembly and effects of DNA methylation.
abstract: The nucleosome is the fundamental packing unit of the eukaryotic genome, and CpG methylation is an epigenetic modification associated with gene repression and silencing. We investigated nucleosome assembly mediated by histone chaperone Nap1 and the effects of CpG methylation based on three-color single molecule FRET measurements, which enabled direct monitoring of histone binding in the context of DNA wrapping. According to our observation, (H3-H4)2 tetramer incorporation must precede H2A-H2B dimer binding, which is independent of DNA termini wrapping. Upon CpG methylation, (H3-H4)2 tetramer incorporation and DNA termini wrapping are facilitated, whereas proper incorporation of H2A-H2B dimers is inhibited. We suggest that these changes are due to rigidified DNA and increased random binding of histones to DNA. According to the results, CpG methylation expedites nucleosome assembly in the presence of abundant DNA and histones, which may help facilitate gene packaging in chromatin. The results also indicate that the slowest steps in nucleosome assembly are DNA termini wrapping and tetramer positioning, both of which are affected heavily by changes in the physical properties of DNA.
authors.affiliation: From the Department of Chemistry and the Huck Institutes of the Life Sciences, The Pennsylvania State University, University Park, Pennsylvania 16802.
authors.forename: Ju Yeon
authors.initials: JY
authors.lastname: Lee
authors.affiliation: From the Department of Chemistry and the Huck Institutes of the Life Sciences, The Pennsylvania State University, University Park, Pennsylvania 16802.
authors.forename: Jaehyoun
authors.initials: J
authors.lastname: Lee
authors.affiliation: From the Department of Chemistry and the Huck Institutes of the Life Sciences, The Pennsylvania State University, University Park, Pennsylvania 16802.
authors.forename: Hongjun
authors.initials: H
authors.lastname: Yue
authors.affiliation: From the Department of Chemistry and the Huck Institutes of the Life Sciences, The Pennsylvania State University, University Park, Pennsylvania 16802 txl18@psu.edu.
authors.forename: Tae-Hee
authors.initials: TH
authors.lastname: Lee
mesh_terms: D000818:Animals; D042002:Chromatin Assembly and Disassembly; D004247:DNA / Q000737:chemistry / Q000378:metabolism*; D019175:DNA Methylation; D031541:Fluorescence Resonance Energy Transfer; D006657:Histones / Q000737:chemistry / Q000378:metabolism*; D056490:Nucleosome Assembly Protein 1 / Q000378:metabolism*; D009707:Nucleosomes / Q000737:chemistry / Q000378:metabolism*; D011485:Protein Binding; D029701:Saccharomyces cerevisiae Proteins / Q000378:metabolism*; D014982:Xenopus laevis / Q000378:metabolism
chemical_list: D006657:Histones; C533556:NAP1 protein, S cerevisiae; D056490:Nucleosome Assembly Protein 1; D009707:Nucleosomes; D029701:Saccharomyces cerevisiae Proteins; D004247:DNA
keywords: DNA Methylation; Fluorescence Resonance Energy Transfer (FRET); Histone Chaperone; Nucleosome; Single-molecule Biophysics