title: Chromatin compaction under mixed salt conditions: opposite effects of sodium and potassium ions on nucleosome array folding.
abstract: It is well known that chromatin structure is highly sensitive to the ionic environment. However, the combined effects of a physiologically relevant mixed ionic environment of K(+), Mg(2+) and Na(+), which are the main cations of the cell cytoplasm, has not been systematically investigated. We studied folding and self-association (aggregation) of recombinant 12-mer nucleosome arrays with 177 bp DNA repeat length in solutions of mixtures of K(+) and Mg(2+) or Na(+) and Mg(2+). In the presence of Mg(2+), the addition of sodium ions promotes folding of array into 30-nm fibres, whereas in mixtures of K(+) and Mg(2+), potassium ions abrogate folding. We found that self-association of nucleosome arrays in mixed salt solutions is synergistically promoted by Mg(2+) and monovalent ions, with sodium being slightly more efficient than potassium in amplifying the self-association. The results highlight the importance of a mixed ionic environment for the compaction of chromatin under physiological conditions and demonstrate the complicated nature of the various factors that determine and regulate chromatin compaction in vivo.
authors: School of Biological Sciences, Nanyang Technological University, Singapore 637551.
authors: Abdollah
authors: A
authors: Allahverdi
authors: School of Biological Sciences, Nanyang Technological University, Singapore 637551.
authors: Qinming
authors: Q
authors: Chen
authors: School of Biological Sciences, Nanyang Technological University, Singapore 637551.
authors: Nikolay
authors: N
authors: Korolev
authors: School of Biological Sciences, Nanyang Technological University, Singapore 637551.
authors: Lars
authors: L
authors: Nordenskiöld
mesh_terms: D000818:Animals; D002843:Chromatin / Q000737:chemistry* / Q000187:drug effects*; D007477:Ions; D009690:Nucleic Acid Conformation; D009707:Nucleosomes / Q000737:chemistry / Q000235:genetics; D011188:Potassium; D017510:Protein Folding; D012492:Salts / Q000494:pharmacology*; D012964:Sodium
chemical_list: D002843:Chromatin; D007477:Ions; D009707:Nucleosomes; D012492:Salts; D012964:Sodium; D011188:Potassium