Purification and comparative mechanistic studies of an endogenous inhibitor of maize RNA polymerase

Abstract

1. A low molecular weight inhibitor of maize DNA-dependent RNA polymerase (nucleoside triphosphate: RNA nucleotidyltransferase, EC 2.7.7.6) has been purified to chromatographic homogeneity from a high-speed supernatant fraction which also contains the soluble enzyme. 2. Chemical characterization of the inhibitor has revealed the presence of an aromatic nucleus which apparently contains an attached —COOH group and one or more sulfur-containing side chains. 3. Studies using known inhibitors of RNA polymerase for comparative purposes demonstrated that the maize inhibitor acts much the same as α-amanitin in its ability to interrupt polymerization. Initiation by maize RNA polymerase was greatly enhanced in the presence of the maize inhibitor. 4. On the basis of resistance to rifamycins and inhibition by α-aminitin, the soluble maize RNA polymerase was shown to be equivalent to the nucleoplasmic RNA polymerase II of animals.