No abstract

The interaction of F1 histones and DNA was studied by means of circular dichroism spectroscopy and enzymatic assays with DNase I and R N A polymerase. FI histones prepared by trichloroacetic acid extraction from a given animal species were more effective in protecting DNA of that species from DNase hydrolysis, than a similar preparation from a foreign species. Analogous results have been obtained with R N A polymerase assays. Changes in the circular dichroism spectra of DNA-histone complexes were attained at lower histone :DNA ratios when both histone T he genetic material of higher organisms exists as a complex of nucleic acid (DNA and RNA) and chromosomal proteins (histone and nonhistone). When isolated from interphase nuclei, this complex (chromatin) is less active than deproteinized DNA, isolated from the same chromatin, in supporting DNA-dependent R N A synthesis (Huang and Bonner, 1962). The template activity of chromatin may be raised to that of DNA by the selective removal of chromatin-bound histones by techniques which leave nonhistone proteins bound to DNA (Marushige and Bonner, 1966). Evidence for the regulatory role of histones comes from the finding that the template activity of deproteinzed D N A may be reduced by reannealing D N A with histones ( Barr and Butler, 1963); furthermore, histones alter the base composition and nearest-neighbor frequency of the transcribed R N A (Skalka et a/., 1966). Bonner et a/. (1963) have elegantly demonstrated that, by removal of histones from pea bud chromatin, a pea cotelydon-specific R N A could be synthesized. The R N A so produced was found to be capable of directing the synthesis of a cotelydon-specific globulin in an in rxro protein synthesizing system.If histones d o indeed serve some regulatory role, and d o not act solely as structural elements in the architecture of chromosomes, one might expect to see variations in the pattern of distribution of the classes and numbers of histones throughout nature. Several groups (e.g., Crampton et ai., 1957; Fambrough and Bonner, 1966) have failed to detect such variations, while Bustin and Cole (1968) and Panyim