Diurnal rhythm of nuclear RNA polymerase I activity in a duckweed, <italic>Lemna gibba</italic> G3, under continuous light conditions

Abstract

The diurnal change of nuclear RNA polymerases I and II was examined in a longday duckweed, Lemna gibba G3, under continuous light conditions. RNA synthesis in crude nuclei was dramatically stimulated by addition of the exogenous RNA polymerase of Escherichia coli, but not by the addition of calf thymus DNA. Treatment of crude nuclei with the supernatant fractions after precipitation of the nuclei decreased the RNA synthetic activity of the nuclei irrespective of the preparation time of both fractions. RNA polymerase I activity in crude nuclei, which was determined in the presence of α-amanitin at a low concentration of KCl, exhibited a diurnal rhythm but RNA polymerase II activity, which was presumed to be a portion of RNA synthesis inhibited by α-amanitin in the presence of a high concentration of KCl, remained constant throughout the day. Identical results were obtained when both enzymes were solubilized widi ammonium sulfate and chromatographed on DEAE-Sephadex column. Both activities in the supernatant fraction obtained after precipitation of the nuclei did not change diurnally. It was concluded, therefore, that the diurnal rhythm of RNA synthetic activity in the crude nuclei is due to the RNA polymerase I activity and not the RNA polymerase II activity.