Inhibitory effects of alpha-amanitin on RNA synthesis and induction of DOPA-decarboxylase by beta-ecdysone

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 transcription by isolated nuclei of Rhynchosciara americana salivary glands. Characteristics of incorporation and inhibition by alpha-amanitin

A method for the isolation of polytene nuclei from salivary glands cells of the Diptera Rhynchosciara americana is described. The stage-specific morphological pattern of the chromosome is maintained during the isolation. The isolated nuclei show two distinct RNA polymerase activities, namely I and II, characterized on the basis of ionic requirements and alpha-amanitin sensitivity. Studies of the product under the incubation conditions show that the system allows the synthesis of high-molecular weight RNA, beside a low molecular weight peak which may comprise pre-4S and 5S RNAs. Autoradiographic studies carried out in the presence or absence of the toxin alpha-amanitin showed that micronucleoli contain products of RNA polymerase type I activity (ribosomal RNA) and that the DNA puffs are engaged in alpha-amanitin sensitive RNA synthesis and thus are sites of polymerase type II activity.

Studies on the mode of action of ecdysterone in adult female Aedes aegypti

Injection of ecdysterone into non-blood fed adult female Aedes aegypti results in a marked stimulation of aromatic-L-amino-acid decarboxylase (formerly DOPA-decarboxylase) activity (Schlaeger and Fuchs, 1974a). When the hormone and alpha-amanitin are injected either simultaneously or if the toxin is administered first no inhibition of subsequent enzymatic activity is observed and in fact substantial enhancement occurs. Cordycepin injection along with ecdysterone gives results similar to alpha-amanitin. The inhibitors by themselves elicit a very small increase in DOPA decarboxylase activity compared to saline-injected controls. Conversely, actinomycin D causes severe depression of ecdysterone-mediated DOPA decarboxylase activity as dose cycloheximide and puromycin. We interpret our data to mean that the mRNA for DOPA decarboxylase is already present prior to exposure to ecdysterone. We postulate that the function of the hormone would be to modulate translation of specific pre-formed mRNA's by an unknown mechanism or to induce transcription of specific tRNAs necessary for the initation of translation of selecting existing messengers.

Translation of mRNA for 3,4-dihydroxyphenylalanine decarboxylase isolated from epidermis tissue of Calliphora vicina R. -D. in a heterologous system. Dependence of mRNA concentration on the insect steroid hormone ecdysone

RNA was isolated from the epidermis of Calliphora vicina larvae by phenol--chloroform extraction. The RN A sedimenting in sucrose gradients between 5 and 18 S was submitted to chromatography on oligo(dT)-cellulose columns. The fraction binding to the oligo(dT) is able to stimulate protein synthesis in a system consisting of mouse liverribosomal subunits, pH-5 factors from rat liver and initiation factors from rabbit reticulocytes. Optimal Mg2+ concentration for the translation of insect mRNA is 3.5 mM, that of K+ 76 MM. Initiation factors prepared from epidermis of Calliphora larvae are less efficient in the translation of insect mRNA than initiation factors isolated from reticulocytes. The pH-5 fraction from epidermis inhibits protein synthesis independent of the source of the mRNA fraction used. One of the proteins synthesized in the reconstituted system under the direction of insect mRNA has been identified as 3,4-dihydroxyphenylalanine (DOPA) decarboxylase by immunoprecipitation with specific antiserum against DOPA decarboxylase and comigration in dodecylsulphate-acrylamide electrophoresis with pure DOPA decarboxylase. Both mRNA from white prepupae and from 6--7-days-old larvae contain sequences coding for DOPA decarboxylase. However, white prepupae contains 3--4 times more DOPA decarboxylase-mRNA than 6--7-days-old larvae. The content of DOPA decarboxylase mRNA is proportional to the amount of active DOPA decarboxylase molecules present in the animals from which the mRNA was isolated.

Rapid enhancement of chick intestinal DNA-dependent RNA polymerase II activity by 1 alpha, 25-dihydroxyvitamin D3, in vivo

1alpha,25-dihydroxyvitamin D(3) was examined for its ability to affect the DNA-dependent RNA polymerases (nucleosidetriphosphate:RNA nucleotidyltransferase, EC 2.7.7.6) of rachitic chick intestinal cell nuclei in vivo. Nucleoplasmic (form II) RNA polymerase activity was stimulated 2-fold (P < 0.05) within 2-3 hr after an oral dose of 0.27 mug (0.65 nmol) of 1alpha,25-dihydroxyvitamin D(3) to rachitic chicks. The form II polymerase activity returned to control values by 5-9 hr after dosing with the sterol. In contrast, the nucleolar (form I) RNA polymerase was not increased within this period. Solubilization of nuclear protein and resolution of the two RNA polymerases on DEAE-Sephadex also revealed that there was an increase in polymerase II activity when assayed on exogenous DNA template. This evidence suggests that 1alpha,25-dihydroxyvitamin D(3) acts at the level of the enzymology of intestinal cell transcription and that increased mRNA synthesis after administration of this hormone cannot be due solely to a change in chromatin template activity.

Effect of the exotoxin of Bacillus thuringiensis on normal and ecdysone-stimulated ribonucleic acid polymerase activity in intact nuclei from the fat-body of Sarcophaga bullata larvae

A nuclear preparation from the fat-body of Sarcophaga bullata was obtained which incorporates nucleotides at a steady rate. Two activities, differing in their response to alpha-amanitin, are present. The activities are not separated by changes in the concentration of (NH(4))(2)SO(4) as effectively as in mammalian nuclei. The activity resistant to alpha-amanitin is stimulated by ecdysone, and both normal and the ecdysone-stimulated activities are inhibited by the exotoxin. The amanitin-sensitive enzyme is also inhibited by exotoxin, but higher concentrations are required.