Specific non-histone protein fractions associated with 'active' chromatin in immunized rats

Non-histone proteins of normal, non-immunized rats and rats immunized with mouse spleen cells were labelled with three different amino acids: [3H]tryptophan, [3H]methionine and [3H]leucine. Chromatin was fractionated at increasing salt concentrations into three fractions: 0.35 M NaCl-soluble, 2 M NaCl-soluble and residual. Non-histone protein fractions F (Mr 12 000) and H (Mr 3 000) highly labelled with [3H]tryptophan, lower with [3H]methionine but not with [3H]leucine, were present mainly in the residual fraction. After DNAse II treatment non-histone protein fractions F and H disappeared in chromatin fractions and were present in Mg2+ soluble fractions which suggests that, similar to the fractions I (Mr below 3 000) and B (Mr 120 000) described previously (5), these fractions may be associated with active transcribed genes.