Essential role of arginine residues in the folding of deoxyribonucleic acid into nucleosome cores.

The kinetic studies of chemical modifications of the lysine and arginine residues of the nucleosome core particle from chicken erythrocytes with large molar excesses of 2,4,6-trinitrobenzenesulfonic acid and 2,3-butanedione, respectively, were performed over 20 mM-2.0 M NaCl. Each modification reaction was divided into the two, a rapid and an extremely slow, pseudo-first-order processes, and the numbers of the exposed and buried residues of the respective amino acids were determined. At very low ionic strength (20 mM boric buffer) all residues were inaccessible to the reagents. Between 0.3 and 0.6 M NaCl the basic amino acid residues in a nucleosome core particle were classified into the following three groups: (1) 42 arginine and 78 lysine residues in the N-terminal and C-terminal regions of the histones that are exposed to solvent, (2) a small number of arginine residues (approximately less than 14 Arg) that are strongly bound to the DNA phosphates, and (3) 48 arginine and 38 lysine residues buried in the globular region of the histone octamer. The results suggest that a small number of arginine residues play an essential role in the folding of DNA into a nucleosome core particle.