Chromatin aggregation changes substantially as pH varies within the physiological range.

Abstract

In vitro at least, changes of pH within the physiological range are important in regulating chromatin aggregation. The extent of aggregation was shown to depend substantially on pH as well as on salt. In the absence of salt and in all of the salt conditions tested as the pH was increased, less and less chromatin was aggregated. The aggregation of half the chromatin in the presence of 0 mM NaCl, 150 mM NaCl, 150 mM NaCl and 1 mM MgCl2, and 2 mM MgCl2 was observed at pH 5.4, 6.0, 7.0, and 8.3, respectively. In 150 mM NaCl, 1 mM MgCl2, chromatin aggregation decreased from 86 to 63% as the pH was changed from 5.9 to 6.8, which is the same pH change reported to occur between interphase and mitosis. H1 dissociation from chromatin was also found to be pH dependent.