Changes in binding between DNA and arginine residues in histone induced by cell crowding

Abstract

Earlier reported alterations of the cytochemical properties of nuclear chromatin correlated with growth stimulation were further investigated with respect to changes in the DNA histone interaction. The alkaline bromphenol blue (BPB) binding reaction was quantitated by microspectrophotometry after DNA extraction either with trichloroacetic acid (TCA) or picric acid (PA). This method was used to differentiate between DNA bound arginine and lysine residues in histone. The BPB binding after TCA hydrolysis reflects both arginine and lysine residues in histone bound to DNA, while the BPB binding after PA hydrolysis mainly reflects the lysine residues. The accessibility of the phosphate groups in the deoxyribonucleoprotein (DNP) complex to basic dyes was studied by acridine orange (AO) microspectrofluorimetry. Gradual changes in the DNP complex of human leukocytes on slide cultures can be induced by cell crowding. This biological system was used in the present work to study the interaction between DNA and histone. The results showed that a gradual increase in AO binding to phosphate groups in DNA was accompanied by a gradual decrease in BPB binding to histone after TCA hydrolysis. After PA hydrolysis, however, the BPB binding to histone remained unchanged. These data indicate that changes in the binding between arginine residues in histone and phosphate groups in DNA play an important role in the earlier reported changes in the cytochemical properties of the DNP complex. This indication was further supported by microspectrophotometric measurements of the PA binding capacity of the cell, which also reflects the arginine residues in histone bound to DNA. The observed changes in binding between arginine residues and phosphate groups in DNP may be of importance for the regulation of the genome function and for the growth activity of the cell.