alpha-Amanitin, a toxic substance from the mushroom Amanita phalloides, is a potent inhibitor of DNA-dependent RNA polymerase II (the nucleoplasmic form) from sea urchin, rat liver, and calf thymus. This compound exerts no effect on the activity of polymerase I (nucleolar form) or polymerase III (also nucleoplasmic). The inhibition is due to a specific interaction with polymerase II or with a complex of DNA and polymerase II.

https://science.sciencemag.org/content/sci/170/3956/447.full.pdf

Specific Inhibition of Nuclear RNA Polymerase II by α-Amanitin

This review gives a comprehensive account of the molecular toxicology of the bicyclic peptides obtained from the poisonous mushrooms of the genus Amanita. The discussion of the biochemical events will be preceded by a consideration of the chemistry of the toxic peptides. The structural features essential for biological activities of both the amatoxins and the phallotoxins will be discussed, also including the most important analytical data. Similar consideration will be given to antamanide, a cyclic peptide, which counteracts phalloidin. In addition, the phallolysins, three cytolytic proteins from Amanita phalloides will be discussed. The report on the biological activity of the amatoxins will deal with the sensitivity of the different RNA-polymerases towards the toxins and with their action on various cell types. Consideration will also be given to systems in which alpha-amanitin was used and can be used as a molecular tool; in the past, many investigators used the inhibitor in molecular biology, genetics, and even in physiological research. As for the phallotoxins, discussion of the affinity of these toxins for actin is provied. Further discussion attempts to understand the course of intoxication by filling in the gap between the first molecular event, formation of microfilaments, and the various lesions in hepatocytes during the intoxication.

Amatoxins, phallotoxins, phallolysin, and antamanide: the biologically active components of poisonous Amanita mushrooms.

INTRODUCTION............................................................ 290 ACTION ON BACTERIA.................................................... 291 General Effects of Rifamycins In Vivo and In Vitro.............................. 291 Interaction of Rifamycins with DNA-Dependent RNA Polymerase (EC 2.7.7.6.) ..... ... 291 Characterization of RNA polymerase......................................... 291 Various steps of the RNA polymerase reaction................................. 291 Structure of RNA polymerase............................................... 292 Which enzymatic step is inhibited by rifamycins?.............................. 292 Complex formation of rifamycins with RNA polymerase......................... 293 Resistance Against the Action of Rifamycins.................................... 293 Relationship Between the Chemical Structure and Biological Activity of the Various Rifamycin Derivatives....................................................... 295 Rifamycins as a Tool in Biochemical Studies.................................... 297 Mode of Interaction Between Rifamycins and Bacterial RNA Polymerase ..... ....... 297 Nature of the enzyme-rifamycin complex..................................... 297 Relation between rifamycin-enzyme complex and enzyme inhibition ...... ........... 297 ACTION ON EUKARYOTES................................................. 298 ANTIVIRAL ACTIVITIES .................................................... 299 Effects on Bacterial Viruses 299 Effects on Mammalian Viruses................................................ 300 Effects on DNA Viruses..................................................... 300 Effects on RNA Viruses..................................................... 301 Effects on Trachoma Agent................................................... 301 CLINICAL APPLICATIONS.................................................. 302 COMPOUNDS RELATED TO THE RIFAMYCINS ............................ 302 SUMMARY AND CONCLUSIONS........................................... 304 LITERATURE CITED........................................................ 304

https://mmbr.asm.org/content/mmbr/35/3/290.full.pdf

Actions of the rifamycins.

Toxins of Amanita phalloides

Animal DNA-dependent RNA polymerases 11. Mechanism of the inhibition of RNA polymerases B by amatoxins

1. α-Amanitin inhibits in vitro the RNA polymerase solubilized from isolated rat liver nuclei. 2. In contrast with previous observations with whole nuclei, the inhibition occurs approximately to the same extent in the presence and in the absence of ammonium sulphate. 3. Evidence is presented that the toxin acts by interacting with the enzyme itself and not with DNA or other components.

/pdf/inhibition-by-a-amanitin-of-ribonucleic-acid-polymerase-30te4fax8g.pdf

Inhibition by α-amanitin of ribonucleic acid polymerase solubilized from rat liver nuclei

The RNA polymerase activity present in the cytoplasm of BHK cells infected with vaccinia virus is not affected by rifampicin or by α-amanitin

L. Fiume

Papers

Inhibition by α-amanitin of ribonucleic acid polymerase solubilized from rat liver nuclei

Ribonucleic Acid Polymerase Induced by Vaccinia Virus: Lack of Inhibition by Rifampicin and α-Amanitin