Methylated basic amino acid composition of histones from the various organs from the rat

Newborn rats received 5 muCi each of [3H]lysine and [methyl-14C]methionine/g body weight. They were killed 10 days later and the nuclei prepared from the kidneys, liver, cerebrum, cerebellum, and thymus. The five major histones were extracted from these nuclei by the method of Johns and further purified on Bio-Gel P-10. The histones were hydrolyzed and the basic amino acids fractionated on Beckman PA-35 resin. Only the F3 and Fia1 histones contained any significant amounts of methylated amino acid residues as measured by chemical or radiological assay. The product of methylation of F2a1 was predominantly dimethyllysine with trace quantities of monomethyllysine detectable in rapidly proliferating tissue. The products of methylation of F3 were mono-, di-, and trimethyllysine in an approximate molar ratio of 0.55:1.0:0.35. This ratio did not vary significantly in the F3 histones prepared from the different organs. No methylarginine or methylhistidine was detected in any of the histones prepared from the five organs. The total amount of dimethyllysine in F2a1 from the different organs of adult rats was approximately 2.0 mol/mol of polypeptide. It appears that the distribution of methyl groups on the lysyl residues in the F3 and F2a1 histones from the different organs is similar and does not contribute to tissue heterogeneity.