Chemical studies of histone methylation. Evidence for the occurrence of 3-methylhistidine in avian erythrocyte histone fractions.

The methyl&ion of histones was studied in mature and immature red cells of the duck. Histone Fractions I, II, III-IV, and V were prepared from cells which had been incubated in the presence of L-methionine-(methyl-3H). The histones were hydrolyzed in acid and the digests were chromatographed on an amino acid analyzer under conditions which have been shown to resolve the methyl derivatives of lysine as well as those of histidine. All of the histone digests were radioactive, due in part to the incorporation of methionine during protein synthesis de nova (Fraction III-IV) and in part to methylation of preformed histones (Fractions I and V). Histone Fractions I and V were found to contain radioactive 3-methylhistidine. The formation of 3-methylhistidine occurs much more rapidly in immature erythroid cells than in the mature erythrocytes.