The chromatin proteins synthesized by phyto-hemagglutinin-stimulated lymphocytes have been investigated using a double isotope labeling approach. Lymphocyte chromatin was dissociated in 0.4 M guanidine-HCl, 6 M urea, 0.1% β-mercaptoethanol, and 0.1 M sodium phosphate buffer at pH 7.0, which solubilized >90% of the total chromatin proteins. The histones and nonhistones were then separated from one another by ion exchange chromatography and analyzed by polyacrylamide gel electrophoresis. The nonhistone chromatin proteins accounted for less than 15% of the total protein in lymphocyte chromatin but they contained >70% of the [3H]leucine incorporated into the chromatin protein during a 2-hr pulse. When lymphocytes were stimulated by phytohemagglutinin, there was a prompt increase in the synthesis of all the nonhistone proteins, but not of histones. Among the nonhistones, several specific proteins were preferentially synthesized during the activation of the cell by phytohemagglutinin.
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