title: Displacement and aberrant methylation in vitro of H-1 histone in rat liver nuclei after half-saturation of chromatin with polycations.
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.
mesh_terms: D000818:Animals; D002412:Cations / Q000494:pharmacology*; D002467:Cell Nucleus / Q000378:metabolism*; D002843:Chromatin / Q000378:metabolism*; D006657:Histones / Q000378:metabolism* / Q000494:pharmacology; D008239:Lysine; D008745:Methylation; D008780:Methyltransferases / Q000378:metabolism; D011107:Polylysine / Q000494:pharmacology; D011479:Protamines / Q000494:pharmacology; D051381:Rats; D012436:S-Adenosylmethionine / Q000378:metabolism; D013095:Spermidine / Q000494:pharmacology
chemical_list: D002412:Cations; D002843:Chromatin; D006657:Histones; D011479:Protamines; D011107:Polylysine; D012436:S-Adenosylmethionine; D008780:Methyltransferases; D008239:Lysine; D013095:Spermidine