[A theoretical model of the mechanism of DNA compactization by polycations].

DNA compactization in the presence of polycationic ligands was analysed theoretically. The concept is substantiated which states that the formation of polycationic bridges between the DNA regions adjoining in the chain is the principal mechanism of compactization. A phase diagram is plotted for DNA transition into the compact state in the coordinates of solution ionic strength and ligand concentration. The ligand binding with DNA under compactization conditions is shown to be characterized by positive cooperativity. DNA compactization by protamines and histones HI is discussed in terms of the results obtained.