Isolation, purification and characterization of RNA polymerases from wheat germ

Demonstration of transcriptional regulation of specific genes by phytochrome action

We have developed an in vitro transcription system that uses nuclei isolated from Lemna gibba G-3. The in vitro transcripts include sequences homologous to hybridization probes for the small subunit of ribulose-1,5-bisphosphate carboxylase [3-phospho-D-glycerate carboxy-lyase (dimerizing), EC 4.1.1.39], the light-harvesting chlorophyll a/b-protein, and rRNA. Light-harvesting chlorophyll a/b-protein sequences are transcribed to a greater extent in nuclei isolated from plants grown in darkness with 2 min of red light every 8 hr than in nuclei isolated from dark-treated plants. Furthermore, the amount of these transcripts measured in plants given a single minute of red light after dark treatment is increased over the amount measured in dark-treated plants. The effect of red light is at least partially reversible by 10 min of far-red light given immediately after the red light pulse. Transcription of both rRNA and small subunit sequences is also stimulated by a single minute of red light as compared to dark-treated tissue. However, the relative magnitudes of the increases compared to the dark levels are smaller than the increase seen for the chlorophyll a/b-protein, possibly because of the higher level of transcription of these sequences in the dark. The effect of red light on the transcription of small subunit and rRNA sequences is also reversible by immediate treatment with 10 min of far-red light. Pulse chase studies of dark-treated nuclei for up to 110 min do not show substantial turnover of in vitro labeled small subunit and chlorophyll a/b-protein transcripts. We therefore conclude that phytochrome action has induced specific changes in transcription of these genes.

A facile procedure for purifying maize chloroplast RNA polymerase from whole cell homogenates

Two DNA-dependent RNA polymerases have been purified from homogenates of maize leaves by a relatively rapid procedure involving Sepharose 4B and DEAE-cellulose chromatography followed by resolution of two RNA polymerasies on phosphocellulose. The RNA polymerase eluting from phosphocellulose at 0.11 M (NH4)2SO4 is inhibited strongly by low levels of alpha-amanitin and possesses catalytic properties and polypeptide subunits like those of maize nuclear RNA polymerase II. The RNA polymerase eluting from phosphocellulose at 0.15 M (NH4)2SO4 resembles the RNA polymerase solubilized from isolated maize chloroplasts in many ways. This enzyme and that isolated from chloroplasts are resistant to alpha-amanitin and rifamycin-SV at high concentrations. Both RNA polymerases have virtually the same Mn2+ and Mg2+ optima, Mg2+/Mn2+ activity ratios, (NH4)2SO4 sensitivity, kinetics of UMP incorporation, and temperature optima. Electrophoresis of this phosphocellulose-purified RNA polymerase on denaturing polyacrylamide slab gels reveals 14 heavily stainable polypeptides that are identical in number and molecular mass to those from chloroplast RNA polymerase. Moreover, two-dimensional tryptic maps of the 14 polypeptides from the phosphocellulose-purified RNA polymerase are very similar to the maps of corresponding polypeptides from chloroplast RNA polymerase. Using this method, relatively large quantities (0.5 mg/kg leaves) of a form of chloroplast RNA polymerase can be prepared in a few days.

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.

A polyethylene glycol/dextran procedure for the isolation of chromatin proteins (histones and nonhistones) from wheat germ

A new procedure is described for the isolation of both histone and non-histone chromatin proteins, based on a polyethylene glycol (PEG)/dextran two-phase partition system. Chromatin is solubilized in high salt (5 M NaC1) and mixed with PEG and dextran to separate proteins (partitioned into the upper, PEG-rich phase) from nucleic acid (DNA recovered almost exclusively in the lower, dextran-rich phase). The proteins are then absorbed onto Bio-Rex 70 by dialysis to low salt (0.05 M NaC1), followed by salt elution to recover first non-histone proteins (less than 0.55 M NaC1), then histones (2 M NaC1). Cross-contamination is not detectable in either group of proteins. The procedure is rapid, gentle, and lends itself well to scale-up. The proteins are kept in pH range 7.0--8.1, and are not exposed to the denaturing reagents characteristic of most preparative procedures for chromatin proteins. Though developed specifically for the isolation of proteins from chromatin of wheat germ, the procedure should be readily applicable to other sources as well. Wheat germ (isolated wheat embryos) appears to be an excellent source of chromatin proteins; 100 g yields 225--300 mg histones and 30--45 mg nonhistone proteins, depending on technique.

Isolation and purification of RNA polymerases from rye embryos

A procedure has been developed for the purification of soluble DNA-dependent RNA polymerase (EC 2.7.7.6) from rye embryos. The enzyme solubilized by high salt extraction with sonication and resolved by DEAE-cellulose chromatography yields two activities. Enzyme I eluted at 0.15 M (NN4)2SO4, was insensitive to alpha-amanitin and was extremely labile. Enzyme II eluted at 0.25 M (NH4)2SO4 was inhibited by alpha-amanitin. However, DEAE-Sephadex chromatography yields three DNA-dependent RNA polymerases. Enzyme I is resistant to amanitin, while II and III enzymes are inhibited by this poison. Partially purified on DEAE-cellulose, polymerase II was further purified by hydrophobic chromatography on an omega-aminobutyl-Sepharose column. After omega-aminobutyl-Sepharose chromatography, enzyme II was stable and was more active with denatured than with native DNA as template. The activity of purified RNA polymerase II is dependent on the DNA, Mn-2+ and Mg-2+ added and requires ATP, GTP, CTP and UTP for its maximum activity. Transcription is inhibited besides by alpha-amanitin, by chromomycin A3, daunomycin, ethidium bromide and actinomycin D. Rifampin and rifamycin SV do not inhibit the enzyme. Synthetic copolymers were also effective as templates.

Ribonucleic acid polymerase activities in Jerusalem artichoke tissue

1. Artichoke tuber tissue contained RNA polymerase activity bound to the chromatin and in the supernatant after chromatin sedimentation. 2. The activity in the supernatant, the soluble polymerase, was fractionated into polymerases I and II by DEAE-cellulose chromatography, and the properties of each activity were determined. 3. The proportions of chromatin-bound and soluble activities varied with growth of the tissue, and there was a correlation between chromatin-bound activity and RNA accumulation. 4. The properties of the solubilized chromatin activity were compared with those of the soluble activity, and the relationship between these two activities is discussed.

Purification and subunit analysis of wheat-germ ribonucleic acid polymerase II

A procedure is described for the purification of the alpha-amanitin-sensitive DNA-dependent RNA polymerase [EC 2.7.7.6] from wheat germ. Solubilization of the enzyme activity was achieved by sonication of a crude extract in a high-salt buffer. Purification involved precipitation with protamine sulphate and (NH(4))(2)SO(4), chromatography on DEAE-cellulose and phosphocellulose, and sucrose gradient centrifugation. Under denaturing conditions the enzyme dissociated into five polypeptides with molecular weights and molar ratios of 220000 (0.9), 170000 (0.1), 140000 (1.0), 45000 (0.2), and 40000 (0.4). Approx. 1mg of purified RNA polymerase was obtained as a routine from 100g of starting material.