The effect of a range of RNA polymerase inhibitors on RNA synthesis in higher plant chloroplasts and nuclei

Abstract

In seeking a specific inhibitor of transcription in higher plant chloroplasts, a range of RNA polymerase inhibitors, which are known to be selective in their actions in other situations, was tested on RNA synthesis in chloroplasts and nuclei from pea, corn, radish, and spinach. The inhibitors tested were rifamycin, streptolydigin, ethidium bromide, proflavine, and α-amanitin. Chloroplast and nuclear RNA synthesis was insensitive to rifamycin both in vivo and in vitro. α-Amanitin at high concentrations had no effect on plastid RNA polymerase and was only slightly inhibitory towards Mn 2+-stimulated RNA polymerase activity of nuclei. Streptolydigin, ethidium bromide, and proflavine inhibited RNA synthesis by isolated chloroplasts and nuclei to about the same extent. No selective inhibitor of chloroplast transcription was found. It is concluded that the RNA-synthesizing system of chloroplasts does not resemble that of bacteria in its reaction to these inhibitors, and RNA synthesis in plant nuclei has different characteristics to that of animal nuclei.