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Sci Rep. 2015 Feb 17;5:8512. doi: 10.1038/srep08512.

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

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1
School of Biological Sciences, Nanyang Technological University, Singapore 637551.

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.

PMID:
25688036
PMCID:
PMC4330525
DOI:
10.1038/srep08512
[Indexed for MEDLINE]
Free PMC Article

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