ABSTRACT
Chromatin, the interphase chromosomal material of eukaryotic cells is a complex of deoxyribonucleic acid (DNA) with a fixed level of histone proteins, variable amounts of nonhistone chromosomal proteins (NHCP), and small amounts of Ribonucleic acid (RNA). Some special requirements in the NHCP isolation and fractionation are due to very difficult solubilization of the whole and especially, dehistonized chromatin. Contrary to cytoplasmic proteases active at lower ionic strength, the activity of the chromatin-bound protease increases in solutions of high ionic strength, being optimal at pH 7.8 to 8.5. A neutral protease of high molecular weight was isolated from rat liver chromatin and characterized by Bonner’s group. Interactions between DNA, RNA, histones, and nonhistones in chromatin involve ionic, hydrophobic, and hydrogen bonds. A few covalent disulfide linkages can also exist between chromatin proteins. Isoelectric precipitation as well as isoelectric fractionation by electrical transport has been, for a long time, among the standard procedures of protein separation.
