Chromatin compaction under mixed salt conditions : opposite effects of sodium and potassium ions on nucleosome array folding

• Main Authors: Allahverdi, Abdollah, Chen, Qinming, Korolev, Nikolay, Nordenskiöld, Lars
• Other Authors: School of Biological Sciences
• Format: Article
• Language: English
• Published: 2015
• Subjects: DRNTU::Science::Biological sciences
• Online Access: https://hdl.handle.net/10356/106981; http://hdl.handle.net/10220/25236
• Institution: Nanyang Technological University

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+, Mg2+ 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 Mg2+ or Na+ and Mg2+. In the presence of Mg2+, the addition of sodium ions promotes folding of array into 30-nm fibres, whereas in mixtures of K+ and Mg2+, potassium ions abrogate folding. We found that self-association of nucleosome arrays in mixed salt solutions is synergistically promoted by Mg2+ 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.