An RNA-histone complex in mammalian cells: the isolation and characterization of a new RNA species

The Biology of Isolated Chromatin: Chromosomes, biologically active in the test tube, provide a powerful tool for the study of gene action

The isolated chromatin of higher organisms possesses several properties characteristic of the same chromatin in life. These include the presence of histone bound to DNA, the state of repression of the genetic material, and the ability to serve as template for the readout of the derepressed portion of the genome by RNA polymerase. The important respect in which isolated chromatin differs from the material in vivo, fragmentation of DNA into pieces shorter (5 x 10(6) to 20 x 10(6) molecular weight) than the original, does not appear to importantly alter such transcription. The study of isolated chromatin has already revealed the material basis of the restriction of template activity; it is the formation of a complex between histone and DNA. Chromatin isolated by the methods now available, together with the basis provided by our present knowledge of chromatin biochemistry and biophysics, should make possible and indeed assure rapid increase in our knowledge of chromosomal structure and of all aspects of the control of gene activity and hence of developmental processes.

Polynucleotides associated with histone preparations

Histone fractions prepared from various sources by acid extraction or by salt dissociation contained small quantities of ribo- and deoxyribo-nucleotides. These nucleotides were small and heterogeneous and were efficiently removed from histone preparations by ionexchange chromatography. They probably represent contaminants, rather than uniquely complexed nucleotides, of all the histone preparations.

Phosphorylation of dipteran chromosomes and rat liver nuclei

Side-chain modifications of the nucleoproteins are believed to be involved in the control of gene function. Rat liver nuclei and chromatin incubated in adenosine triphosphate labeled in the gamma position with phosphorus-32 demonstrated rapid phosphorylation in vitro of the nuclear proteins. Dipteran salivary glands incubated in either labeled adenosine triphosphate or ortho-phosphate labeled with phosphorus-32 showed that there is phosphorylation of chromosomal protein. The phosphorus is associated in protein from both liver and salivary gland nuclei predominantly with phosphoserine.

Acidic proteins of mammalian nuclei: isolation and characterization

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[Possibilities of the regulation of differential DNA activities in higher plants by histone]

By staining calf-thymus histones with fluorescein isothiocyanate and by diazotation it could be shown that externally applied histones enter the cells and accumulate specially in the nucleus. The permeability of the cell membranes does not increase upon application of 100 μg/ml calf-thymus histone (the calf-thymus histone is soluble to less than 50% in water) as measurements of the betacyanin-efflux in tissues of the red beet showed. Application of actinomycin D and calf-thymus histone during the first days of culture (24-72 hrs after culture initiation) inhibits root formation and root growth without diminishing the number of newly formed spots of embryonic cells. Externally applied histone therefore with high probability intervenes mostly in the nucleic acids of the cells.The inhibition of root formation, of differentiation of tracheae and of root growth shows no specific differences upon application of histone from calf-thymus glands or from pea epicotyls or of protamine or poly-1-lysine.With increasing concentration of histone the inhibition of root formation occured over a longer period. After the percentage of free NH2-groups had been diminished by gently acetylation and after the secondary structure had been altered by thermal denaturation of histones, the inhibition of root formation and differentiation of tracheae decreased strongly. The inhibition of root growth, however, still remained. Thermally denatured protamine inhibited root formation and root growth over a longer period than untreated protamine did. The performed acetylation and thermal denaturation hardly lessened the binding capacity of histone to DNA. It is assumed that changes in the histone content of the cells as well as little alterations of histone binding capacity to DNA may play an important role in the regulation of some differential DNA activities by histones and perhaps by other basic proteins.