Hydrogen ion dependent reversible fibrillarization and hydration of chromatin in divalent cation-depleted isolated...

Rat liver cell nuclei isolated in the presence of Ca++ and Mg++ ions were exposed to citrate buffer at different pH levels. Their morphology was studied with the electron microscope and the water content measured. At a low pH the chromatin remained compact, but at neutral pH an intense fibrillarization of the chromatin was observed; and, seemed to be reversible, because of deoxyribonucleoproteins (DNP) filaments which dispersed at a pH of 7 were repacked to their previous site at a pH of 3. The ribonucleo-proteins (RNP)-containing structures did not show the same reversible fibrillarization. In addition to the morphological changes, a large increase in the water content ("water-holding capacity") of the chromatin structures was observed.