Incorporation of various amino acids into non-histone chromatin protein fractions of spleen cells of mice immunized with IgG.

Incorporation of three various amino acids ([3H]-tryptophan, [3H]-methionine or [3H]-leucine) into the non-histone chromatin proteins, synthesized in spleen cells of mice after immunization with IgG, is described. Two new fractions of non-histone chromatin proteins (I-mol. wt. below 3 000 and B1-mol. wt. about 120 000), appearing during the immune reaction were labelled with [3H]-tryptophan and [3H]-methionine but not with [3H]-leucine. Synthesis of these fractions was observed only at the time of maximal RNA synthesis. A suggestion about the role of tryptophan and methionine in non-histone chromatin proteins in the regulatory processes of gene activation is discussed on the basis of their selective binding to DNA.