ABSTRACT
The biological function of histones must be rather general since, with the exception of the F1 (I) histones, these proteins remained virtually unchanged during the evolution of many animal and plant species. It is difficult to escape the impression that the amino acid sequence of each histone fraction is evolutionary fixed and essential for its biological function. From the chemical nature of histones and from their principally electrostatic interactions with the DNA, histones alone cannot function as repressors of specific genes in eukaryotic cells. As indicated by DNA-RNA hybridization studies, the tissue specificity of hybridizable RNA biosynthesized in vitro on normal and reconstituted chromatin templates depends on the origin of the nonhistone protein fraction. The c-RNA-nonhistone protein complex associates with the histones, presumably by hydrogen bonds, which can be dissociated by guanidine hydrochloride. In chromatin, the c-RNA is resistant to RNase, perhaps because it exists in the form of a hybrid with complementary DNA.
