Mixed iron–cobalt binuclear complexes. Part I. Identification of mixed complexes derived from trans-[Co(en)₂(H₂O)(SO₃)]⁺

On Mechanisms Determining the Interrelationships between DNA and Histone Components of Chromatin

“…It is known that the increase in the degree of polymerisation of ionic ligand to the definite value leads to strengthening the interaction between the ligand and an oppositely charged polyion. This dependence on the degree of polymerisation of the ligand is not very pronounced above its quite moderate values [3]. The critical degree of polymerisation seems to be determined by the size of the statistical segment of the ligand, i. e. by degree of mutual correlation of ligand monomers.…”

“…Since the appearance of the hypothesis about the repressive role of histones in chromosomes [l], for over a quarter of a century DNA-histone interactions have been a matter of steady interest to researchers studying the mechanisms of gene regulation in eucaryotic cells. The discovery of chemical heterogeneity of the histone component of chromatin has made it necessary to explore separate histone fraction affinities for DNA, because the principle of the biological molecule affinity lies at the foundation of all living processes [2] and determines biological specificity [3]. The histone affinity for DNA has been studied in two principal ways : (a) by investigation of DNA-histone complex decomposition, i. e. of histone dissociation from DNA, by modification of the medium into which the extracted chromatin is inserted [4-171; and (b) investigation of DNA-histone complex formation in the mixtures of DNA and whole histone [9,18,19] or in the mixtures of DNA and single histone fractions Two types of solvent modifications have been used in the experiments mentioned above : (a) modifications leading to variation of ionic solvate shells of interacting [20 -221. molecules without change in their charges, alterations (near neutral pH) of ionic strength and ionic composition of solvent [4-6,8,9,13 -15,18,20-221, addition of urea [7 -9,191, of alcohols [8,23,24], and of neutral detergents [13,14] to water/salt solutions; (b) the modifications leading to variation in the electrostatic charges of interacting components, addition of ionic detergents to water/salt solutions [lo-12,15,25], acid titration [16], alkaline titration [17].…”