Structural transition in chromatin induced by ions in solution

Abstract

Structural transition in chromatin was measured as a function of counter ions in solution (NaCl or MgCl(2)) and of histones bound on the DNA. The addition of counter ions to aqueous solutions of chromatin, partially dehistonized chromatin, and DNA caused a drastic reduction in viscosity and a significant increase in sedimentation coefficient. Transitions occurred primarily at about 2 x 10(-3) M NaCl and 1 x 10(-5) M MgCl(2) and are interpreted as a change in structure of chromatin induced by tight binding of cations (Na(+) or Mg(++)) to DNA, either free or bound by histones, and is an intrinsic property of DNA rather than of the type of histone bound. At a given ionic condition, removal of histone H1 from chromatin had only a minor effect on the hydrodynamic properties of chromatin while removal of other histones caused a drastic change in these properties. An increase in the sedimentation coefficient of DNA was observed also for protamine. DNA complexes wherein the bound protein contains only unordered coil rather than the alpha-helices found in histones.

Chromatin fiber dimensions and nucleosome orientation : a neutron scattering investigation

“…The early and important work of Zubay and Doty (22) showed that the intrinsic viscosity and light scattering do not vary in a plateau between .5 and 1.5 mM salt, but that at higher concentrations aggregation occurred, and below .5 mM salt,electrostatic repulsions become quite large and perhaps destroy the native structure. Similar transitions with salt have been observed and put into a more current context (23,24,25). Consequently, we have generally confined our scattering studies to the plateau region around 1 mM salt, but we note that our measurements at lower and higher ionic strength may suggest the onset of aggregation at about 10 mM salt and denaturation below .5 mM.…”

Structural elements in adenovirus cores

“…For example, LI et al (14) found out that 10 .3 to 10 -2 M NaCl had no effect on C.D. It seems to influence not only the interaction between 'rods' (most probably by competing for calcium), but also the DNA-protein association manifested by the appearance of free DNA filaments.…”

Ionic strength‐dependent conformational transitions of chromatin. Circular dichroism and thermal denaturation studies

“…Olins and coworkers45 have reported a similar unfolding transition, followed by sedimentation and diffusion constant measurements, in isolated core particles over the same range of ionic strengths reported above. 44 This transition could also be followed by changes in fluorescence of an extrinsic fluorophore attached to H3.46347 The electron-microscopic studies of Oudet and c~w o r k e r s~~,~~ suggest that these apparent unfolding transitions in solution may result in the breakdown of nucleosomes into "half-nucleosomes." Such a transition has interesting biological implications and deserves further attention.…”