Effect of in vitro (ADP)ribosylation on transcription of the chromatin of the brain of developing rats.

The template-engaged RNA polymerase II was assayed in the nuclei purified from the cerebral hemisphere of 3-, 14- and 30-day old rats. Its activity is the highest at 3-day and declines as development proceeds. Lower transcription at 30-day may either be due to a decrease in the active fraction of chromatin or to a decrease in the amount of RNA polymerase II that is active towards endogenous template, or both. The activity of RNA polymerase I (active in low salt) is also maximal at 3-day and declines as development proceeds. (ADP)ribosylation of chromatin depresses RNA synthesis. This may be due to inactivation of RNA polymerase itself by protein poly(ADP)ribosylation.