Effect of cGMP on RNA polymerase II activities in fetal calf liver nuclei and in purified enzyme preparations.

During a study on the role of cyclic nucleotides on the RNA polymerase activities of isolated fetal calf liver nuclei, it was observed that cGMP enhanced the RNA polymerase activity in the presence of Mg++ at low ionic strength, conditions which are appropriate for the measurement of the RNA polymerases I and III. However, the cGMP-dependent stimulation was sensitive to low concentrations of alpha-amanitin, indicating an effect on the activity of the RNA polymerase II. For this reason the effect of cGMP was tested again using purified RNA polymerase II preparations from calf thymus devoid of RNA polymerases I and III. cGMP stimulated activity of the purified RNA polymerase II at concentrations of 1 and 10 nM. cGMP also caused a small but significant stimulation of the protein kinase activity associated with the enzyme preparations of the RNA polymerase used.