Isolation and Properties of Structured Chromatin from Guerin Ascites Tumour and Rat Liver

The method proposed by Hancock for isolation of structured chromatin from tissue culture cells is modified and used for isolation of chromatin from Guerin ascites tumour and rat liver. Micrococcal nuclease digestion patterns and thermal denaturation of these chromatins are studied and cornpared with those of chromatins prepared by precipitation and extraction with salts (salt chromatins). In contrast to the multiphasic melting profiles of salt chromatins, the structured chromatins exhibit relatively homogeneous denaturation patterns under a variety of conditions, suggesting that their DNA is uniformly stabilized by histones and there are no free independently melting DNA stretches. Digestion of structured chromatin with micrococcal nuclease yields a characteristic pattern of fragments, showing that the subunit structure of the deoxyribonucleoprotein is intact. No discrete fragments are formed upon digestion of salt chromatin.