Viscosity of chromatin solutions increases with increasing ionic strength

Abstract

Increasing the ionic strength of rat liver chromatin solutions above 0.4 M causes increasing viscosity. This indicates transformation of the compact chromatin molecules to more elongated forms. In the range of 0.4-0.5 M ionic strength histone H1 is dissociating continuously from the chromatin and the quaternary structure chromatin unravels. At ionic strength higher than 0.5 M the viscosities of chromatin solutions are furthermore increasing due to structural deformation. Near 0.7 M ionic strength the core histones H2A and H2B begin to dissociate from the chromatin, and the opening of the nucleosome cores leads to increasing elongation of the chromatin molecules.

Increased Intracellular Ionic Content Is Correlated with a Decreased Perichromatin Granule Density in Old Neurons

“…Thus, the gradual separation of nonhistone proteins from DNA, due to the higher ionic content, may be responsible for the significant reductions in the efficiency of transcription mechanisms. The unfavorable effects of increased ionic strength on chromatin functions are also supported by literature data reporting the following: (1) that the increase of intracellular ionic content may be responsible for condensation;1 and (2) that an increase of positive charges (e.g., Na + and K + ) in the medium may neutralize the DNA 2. On the basis of these data, the age‐related increase of the monovalent electrolyte content in the neuronal nucleoplasm documented by our results suggests that in the nerve cells of adult and old animals the chromatin physicochemical state and functionality may be negatively conditioned by the higher strength of the ionic milieu.…”

“…With advancing age, an intracellular water loss is reported to occur;10 thus, our findings support the notion that the increase of ionic strength in the nucleoplasm of old neurons is probably much higher than the value that can be calculated by measuring the percentage of biological dry mass of each ion. A physiological value of intracellular ionic strength is very important for chromatin functions, since it is reported to modulate the viscosity of the nucleoplasm and the activity of critical nuclear enzymes, such as RNA polymerase 1,2,15. Thus, the gradual separation of nonhistone proteins from DNA, due to the higher ionic content, may be responsible for the significant reductions in the efficiency of transcription mechanisms.…”

“…Among the factors able to modulate chromatin functions, the qualitative and quantitative composition of the intranuclear ionic milieu is reported to play a critical role in determining the chromatin physicochemical state and functionality 1. Accordingly, slight changes in the ionic strength of chromatin solutions are reported to affect chromatin structures by inducing histone dissociation 2. The structural constituents of the interphase nucleus were finely classified some decades ago3–5 and are still extensively investigated 6,7.…”

Affinity Proteomics to Study Endogenous Protein Complexes: Pointers, Pitfalls, Preferences and Perspectives

“…To solve this problem we apply a very limited degree of low power microprobe sonication to the crude extract, and the aggregates are readily dispersed and homogenized (13). Additionally, human cell powders can occasionally generate viscous extracts depending on the extraction solution used (e.g., high salt or urea, due to the unfolding of chromatin) (113–115)—the same sonication treatment also resolves this problem. With E. coli , viscous extracts are almost always observed, further supporting our contention that while cell breakage via cryomilling is observed to be thorough, it provides an extract whose qualities parallel gentle (e.g., enzymatic and freeze-thaw) breakage methods (103).…”