Reduced Transcription Activity of Rat Liver Chromatin after Protein Restriction and Selective Digestion of Nuclei with Micrococcus Nuciease

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Abstract
Restriction of protein intake in the diet has been shown to produce a change in transcription activity as determined in vitro. Conditions for a reduced transcription activity were investigated with selective digestion of nuclei with micrococcus nuclease (EC 3.1.4.7). Liver nuclei from young male rats fed a diet containing either 20 or 3% casein for 6 days were digested with 1.3 µg of micrococcus nuclease protein/mg of nuclear DNA (specific enzyme activity 15,000 or 150 units/mg of protein). Part of the chromatin-bound RNA polymerase activity was transferred from the 2,000 × g to the 102,000 × g pellet. Independent of the type of endonuclease used, the specific activity of chromatin-bound and soluble RNA polymerase I plus III was similar in the two groups of rats. After protein restriction RNA polymerase II activity was significantly diminished in the 2,000 × g pellet, and was unchanged in the 102,000 × g pellet. Heparinstimulated and soluble RNA polymerase II activities were significantly reduced. Number and length of RNA chains synthesized by chromatin-bound RNA polymerase I plus III remained unchanged by dietary treatment. After a low protein diet, RNA polymerase II in the absence and presence of heparin synthesized an unchanged number of RNA chains with reduced length. A selective digestion of chromatin with micrococcus nuclease is needed to show the reduction in RNA polymerase II activity after protein restriction.