The Effect of Trypsin on Nuclease-resistant Chromatin Fragments

Abstract

Abstract Fragments of calf thymus chromatin that selectively resist micrococcal nuclease digestion are found to be highly compact nucleoprotein particles, each containing a single piece of tightly folded or supercoiled DNA. These particles exhibit an anomalous CD spectrum, and melt in the upper end of the chromatin melting range. Upon trypsin digestion, only about 20% of the protein is removed, but the properties of the particles are greatly modified. They unfold, as judged from hydrodynamic studies, the CD spectrum becomes very much like that of DNA, and the melting point drops by about 20°. We conclude that proteins in the particles serve to maintain the compact structure.