title: Condensation of chromatin in situ by cation-dependent charge shielding and aggregation.
abstract: Binding of di- or polyvalent cations is necessary to maintain the chromatin in isolated nuclei and metaphase chromosomes in a condensed state. We here show that the native, porous structure of the heterochromatin in the interphase nucleus requires both K(+) and Mg(2+) in concentrations, which are known to support transcription in isolated nuclei, thus providing a functional state of the chromatin. When these cations are acting separately, the chromatin is more condensed by Mg(2+) and decondensed by K(+). Comparison with published values of the free electrostatic energy of DNA in chromatin shows that this state of compaction is the result of a balance between the different aggregative properties of K(+) and Mg(2+) at a high degree of charge shielding.
authors.affiliation: Department of Medical Biochemistry and Genetics,Faculty of Health Sciences, University of Copenhagen, Blegdamsvej 3c, 2200 Copenhagen N, Denmark. engelhardt@imbg.ku.dk
authors.forename: Mogens
authors.initials: M
authors.lastname: Engelhardt
mesh_terms: D000818:Animals; D002412:Cations / Q000494:pharmacology; D002467:Cell Nucleus / Q000187:drug effects / Q000648:ultrastructure; D002843:Chromatin / Q000737:chemistry / Q000648:ultrastructure*; D008274:Magnesium / Q000494:pharmacology*; D008297:Male; D011188:Potassium / Q000494:pharmacology*; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: D002412:Cations; D002843:Chromatin; D008274:Magnesium; D011188:Potassium