ABSTRACT
We calculate the binding energy of on- and off-center hydrogenic impurities in a parabolic quantum dot subjected to an intense high-frequency laser field. An exactly solvable model that replaces the actual Coulomb interaction with the donor by a non-local separable potential is introduced for calculating the binding energy. The separable potential allows us to solve the problem exactly and all calculations are carried out analytically. The action of the laser irradiation results in dressed Coulomb and confinement potentials. At low laser intensity the binding energy is found to decrease when the impurity is shifted away from the origin. At high laser intensity and strong confinement the opposite behavior is observed. We propose a simple one-dimensional model that explains the observed crossover.
ABSTRACT
Hen erythrocyte chromatin was treated with trypsin immobilized on collagen membranes and the unfolding of chromatin fiber was followed by light scattering at 90 degrees and flow linear dichroism. Chromatin was found almost completely decondensed when the bulk of H1 and H5 was digested while H3 was still intact. Further digestion leading to degradation of both H3 and the rest of H1 and H5 accounted for no more than 10-15% of the total effect. When chromatin with trypsin-cleaved H1 and H5 was titrated with increasing amounts of spermidine it folded similarly to the control sample. This finding suggests that charge neutralization appears a likely mechanism for maintaining the structure of the 30 nm chromatin fiber by the C-terminal domain of H1 and H5.
Subject(s)
Chromatin , Enzymes, Immobilized/pharmacology , Trypsin/pharmacology , Animals , Chickens , Chromatin/analysis , Female , Histones/metabolism , Light , Scattering, RadiationABSTRACT
Cation-induced folding of 10 nm chromatin filament to 30 nm fiber was studied with hyperacetylated chromatin using light scattering at 90 degrees and flow linear dichroism. Acetylated chromatin folded in a way indistinguishable from that of the control chromatin: both the compactness of chromatin and the orientation of nucleosomes relative to the fiber axis were identical at a given salt concentration.
