The effect of a range of RNA polymerase inhibitors on RNA synthesis in higher plant chloroplasts and nuclei

Autonomously replicating RNA in mitochondria of maize plants with S-type cytoplasm

Mitochondria isolated from maize plants with S-type male-sterile cytoplasms are capable of synthesizing four species of RNA at concentrations of actinomycin D that eliminate all DNA-directed RNA synthesis. No RNA synthesis occurs under the same conditions with mitochondria from plants possessing normal (N) cytoplasm or with other subcellular fractions from plants with S cytoplasm. The actinomycin D-resistant RNA synthesis occurs within the mitochondria since the labeling of these species is unaffected by inclusion of RNase in the incubation medium and since they become completely sensitive to RNase upon lysis of the mitochondria with low concentrations of Triton X-100. Two of the actinomycin D-resistant products are double stranded. These are 2850 and 900 base pairs in length, whereas the remaining two are 2150 and 850 bases. The synthesis of all four RNAs occurs in at least five different accessions of S cytoplasm, suggesting it is a general feature of S mitochondria. The double-stranded RNAs show homology to single-stranded S mitochondrial RNA but not to N mitochondrial RNA. Our observations indicate that the replication of these RNAs occurs independently of mtDNA and that they thus represent a novel type of inheritable element in organelles, an RNA plasmid.

Detection of avocado sunblotch viroid in chloroplasts of avocado leaves by in situ hybridization

In situ hybridization experiments were carried out to detect avocado sunblotch viroid (ASBVd) in foliar tissue of avocado, using a digoxigenin-labelled RNA probe complementary to the ASBVd-RNA in sections of aldehyde-fixed, LRGold-embedded leaf samples. Detection of the probe was made through anti-digoxigenin antibody and protein-A colloidal gold (20 nm). Seventy to 80% of the signals came from chloroplast while the cytoplasm and vacuole were labelled with ca. 10% of the gold particles. This is in contrast with the subcellular localization of potato spindle tuber viroid and some other related viroids, which are mainly found in the nucleus.

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.

Kinetic analysis of fraction I protein biosynthesis in young protoplasts of tobacco leaves

At maximum inhibition chloramphenicol reduced [35S] methionine incorporation into acid-insoluble materials of sterile protoplasts from young tobacco leaves 5-7 cm in length by 30% compared to 70% by cycloheximide, indicating that 30% of the [35S] methionine became incorporated into chloroplast proteins and 70% into cytoplasmic proteins. [35S] Methionine became incorporated into both the large and small subunits of Fraction I protein, the major soluble protein of chloroplasts. Rifampicin and streptolydigin inhibited [3H] uridine incorporation into the 23 and 16 S rRNAs of chloroplasts to a much greater extent than into the 25 and 18 S cytoplasmic rRNAs. Rifampicin inhibited [35S] metionine incorporation into Fraction I protein after the third hour of incubation; streptolydigin after 2 h, the former evidently preventing initiation of mRNA for the large subunit of Fraction I protein and the latter its elongation. About 2.5 h was required between initiation of the large subunit mRNA synthesis, and appearance of the protein. It was estimated that 45 min is required for transcription of the mRNA which has a half-life of 2 h and that 105 min is required for its translation into approximately 350 amino acids constituting the large subunit monomeric polypeptide. The effect of chloramphenicol, cycloheximide and 2-(4-methyl-2,6-dinitroanaline)-N-methyl propionamide, the latter an inhibitor of protein initiation by 80 S ribosomes, on kinetics of Fraction I protein synthesis indicate that protoplasts contain a pool of small subunit polypeptides and that 30 min is required to polymerize the approximately 100 amino acids constituting the primary structure.

Light-induced increase in the activity of maize plastid DNA-dependent RNA polymerase

Illumination of dark-grown maize plants induces a rapid rise in DNA-DEPENDENT RNA polymerase activity in plastids. Within 16 h illumination the enzyme activity is isolated plastids increases 3-4 fold as compared to other dark-grown plants illuminated for only 2 h. This change in activity is unaccompanied by either a quantitative rise in the amount of chloroplast RNA polymerase or qualitative changes in the purified enzyme. It is suggested that other factors may be present which interact either with the enzyme or the DNA template and that these factors are responsible for the light-induced enhancement of the RNA polymerase activity inplastids.

Quantitative studies on ferredoxin in greening bean leaves

Two methods of measuring small amounts of the iron-sulphur protein ferredoxin are described. One involves measurements of the signal at g=1.96 produced by reduced ferredoxin in an e.p.r. (electron-paramagnetic-resonance) spectrometer; the other depends on the rate of ferredoxin-dependent electron transport in a chloroplast bioassay measured in an O(2) electrode. These methods of measurement were used to examine the development of ferredoxin during the greening of etiolated bean leaves. Ferredoxin is present in low concentrations in the leaves and cotyledons of 14-day-old etiolated beans (Phaseolus vulgaris L. var. Canadian Wonder), and develops in a linear manner with time when the leaves are illuminated. This synthesis appears to be independent of chlorophyll synthesis during the early stages of greening. However, the chlorophyll/ferredoxin ratio reaches a final value of approx. 360 irrespective of the light intensity, indicating the existence of a control mechanism operative in deciding the stoicheiometry of these components in the mature chloroplast. The ferredoxin synthesis appears to be light-dependent, and red light is the most effective in its promotion. The effect of red illumination is not reversed by far-red light, indicating the absence of a phytochrome control of ferredoxin synthesis. From experiments using specific inhibitors of chloroplast protein synthesis, it is concluded that ferredoxin is synthesized on cytoplasmic ribosomes.

Control of the synthesis of a major polypeptide of chloroplast membranes in Chlamydomonas reinhardi

The regulation of the synthesis of one of the major polypeptides of chloroplast membranes in Chlamydomonas reinhardi y-1 has been studied in order to determine what factors are involved in the control mechanism. The polypeptide is synthesized in the cytoplasm and previously was designated as c (J. K Hoober. 1972. J. Cell Biol.52:84). Under normal conditions the synthesis of polypeptide c appears to be coupled to the synthesis of chlorophyll. When greening cells are illuminated through a light filter opaque below 675 mmicro, the conversion of protochlorophyllide to chlorophyllide is blocked. Although this elimination of light below 675 mmicro, does not affect, in the main, protein synthesis in the chloroplast and cytoplasm, synthesis of polypeptide c is inhibited. Also, control cells synthesize neither chlorophyll nor polypeptide c in the dark. However, when cells are treated with chloramphenicol, an inhibitor of chloroplast protein synthesis, the synthesis of polypeptide c occurs in the absence of light required for chlorophyll synthesis. Chlorophyll per se does not appear to be required for synthesis of polypeptide c, since treating cells with hemin, maleate, or malonate causes an inhibition of the synthesis of chlorophyll but not of polypeptide c. The results of these experiments are discussed in terms of a proposed mechanism by which synthesis of polypeptide c is regulated at the transcriptional level by a precursor of chlorophyll, and this regulation is mediated by a protein or proteins synthesized within the chloroplast.

RNA polymerases of maize: partial purification and properties of the chloroplast enzyme

A DNA-dependent RNA polymerase has been solubilized and partially purified from washed chloroplasts prepared from maize seedlings. The purified enzyme was completely dependent on added DNA after purification by phospho- or DEAE-cellulose chromatography. On glycerol density gradients, the enzyme ran ahead of a marker with a sedimentation constant of 18 S, indicating a molecular weight of 500,000 or more. The instability of the highly purified enzyme made intensive study difficult, but the properties of the enzyme purified by phosphocellulose chromatography are reported. Template specificity varied during purification but the activity was always higher with denatured than with native DNA and the preference for maize DNA over calf-thymus DNA increased during purification. The enzyme required magnesium for optimal activity, was inhibited by salt concentrations in excess of 0.1 M, and had a temperature optimum of 48 degrees C. The chloroplast enzyme differed from similar activities so far reported from maize or other sources, particularly in the high salt concentrations needed to elute it from phosphocellulose. The soluble, DNA-dependent enzyme was not inhibited by either alpha-amanitin or by rifamycin-SV under the assay conditions used.