ABSTRACT
Chromatin, the interphase chromosomal material of eukaryotic cells is a complex of DNA with a fixed level of histone proteins, variable amounts of nonhistone chromosomal proteins (NHCP), and small amounts of RNA. Moreover, some special requirements in the NHCP isolation and fractionation are due to very difficult solubilization of the whole and especially, dehistonized chromatin. Electrophoretic analysis of proteins in the lyophilized extracts revealed prominent specific NHCP bands with molecular weights of approximately 44,000 and 62,000. Little attention has been given to the effects of proteolysis on the interpretation of chromatin dissociation or reassociation experiments as well as on polypeptide composition of NHCP in their electrophoretical patterns. Since the experiments of A. L. Dounce and T. H. Lan who used saponin to isolate chicken erythrocyte nuclei, many efforts have been exerted to eliminate cytoplasmic and membrane contamination in nuclear preparations used as starting material for the isolation of chromatin and chromosomal proteins.
