ABSTRACT
The occurrence of histones in differentiated organisms, as compared with their absence in bacteria, suggests that the proteins play a role in the genetic regulation of differentiated cells. Quantitative differences in the inhibition of the in vitro RNA synthesis directed by DNA complexed with various histone fractions were also observed by Huang et al. If the reconstitution was made with histones and dehistonized chromatin instead of pure DNA, the resulting complex exhibited a template activity which was as quantitatively and qualitatively restricted as was the original chromatin. Nonhistone proteins, were necessary to obtain the ordered DNA-histone association which results in the tissue specific restriction of DNA in chromatin. Since the selective removal of histone fractions from isolated chromatin resulted in the derepression of qualitatively different segments of DNA, the in vivo specificity of the DNA-histone interactions must be directed by other molecules.
