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  • Title: Displacement and aberrant methylation in vitro of H-1 histone in rat liver nuclei after half-saturation of chromatin with polycations.
    Author: Byvoet P, Baxter CS, Sayre DF.
    Journal: Proc Natl Acad Sci U S A; 1978 Dec; 75(12):5773-7. PubMed ID: 282603.
    Abstract:
    Radiomethyl incorporation in vitro into Nepsilon-methyllysine of histones from rat liver nuclei incubated in the presence of S-adenosyl[methyl-3H]methionine is stimulated if the polycations polylysines, protamines, or histones are added to the incubation mixture. Maximal stimulation occurs at a cation/nucleotide ratio of 0.5. Past this point stimulation drops, except in the case of very lysine-rich histone H-1, for which the maximal level of incorporation remains constant upon further addition of this histone. Bio-Gel P-10 chromatography, differential precipitation, and gel electrophoresis of radiomethylated histones indicate that although the usual incorporation of radiomethyl into histone H-3 is not affected, active methylation of H-1 occurs in the presence of polycations. Column chromatographic amino acid analysis reveals that the methylation of H-1 will specifically generate Nepsilon-monomethyllysine. Except for this condition, H-1 is never methylated in vivo or in incubated cell nuclei. Because H-1 is the weakest bound histone in chromatin, the above phenomena may be explained by assuming that, within the chromatin, polycations displace the lysine-rich histone towards the nucleosome, which results in its abberant methylation, assuming that the native nucleosome is the seat of the histone lysine methyltransferase.
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