Specific inhibition of Rous sarcoma virus by -amanitin

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

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.

In vitro synthesis of Rous sarcoma virus-specific RNA is catalyzed by a DNA-dependent RNA polymerase

Synthesis of Rous sarcoma virus RNA was examined in vitro with a new assay for radioactive virus-specific RNA. Nuclei from infected and uninfected cells were incubated with ribonucleoside [alpha-(32)P]triphosphates, Mn(++), Mg(++) and (NH(4))(2)SO(4). Incorporation into total and viral RNA proceeded with similar kinetics for up to 25 min at 37 degrees . About 0.5% of the RNA synthesized by the infected system was scored as virus-specific, compared to 0.03% of the RNA from the uninfected system and 0.005% of the RNA synthesized by monkey kidney cell nuclei. Preincubation with DNase or actinomycin D completely suppressed total and virus-specific RNA synthesis. alpha-Amanitin, a specific inhibitor of eukaryotic RNA polymerase II, completely inhibited virus-specific RNA synthesis, while reducing total RNA synthesis by only 50%. We conclude that tumor virus-specific RNA is synthesized on a DNA template, most probably by the host's RNA polymerase II.

Inhibition of influenza virus replication by -amanitin: mode of action

The replication of influenza virus in chick embryo fibroblast cells is inhibited by alpha-amanitin added during the first 2 hr of infection at concentrations similar to those required to inhibit cellular DNA-dependent RNA polymerase form II in vivo. Of two periods of increased RNA synthesis observed in cells infected with influenza virus, only the first, occurring from 0 to 2 hr after infection, is sensitive to alpha-amanitin. During this early period, there is a stimulation of the activity of DNA-dependent RNA polymerase II of nuclei isolated from infected cells. The data suggest that DNA transcription mediated by polymerase II is essential for influenza virus replication.