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  • RNA editing  (5)
  • chlorine-35  (5)
  • 1
    ISSN: 1432-0983
    Keywords: RNA editing ; Tomato mitochondria ; coxl gene ; Initiation codon
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Nucleotide-sequence analysis showed that the gene for cytochrome oxidase subunit I (coxl) from tomato mitochondrial DNA has an ACG codon at a conserved position corresponding to an ATG initiation codon in other higher-plant coxl genes. cDNA-sequence analysis of the coxl transcripts showed that 15 positions in the genomic DNA were converted from C to U in the transcripts by RNA editing. One of the editing events is observed at the indicated ACG codon, producing an ATG initiation codon. The nucleotide sequences of 37 cDNA clones showed that the initiation codon was created in 32 out of the 37 clones, while nucleotide positions 254 and 11 were edited in 37 and 34 of the 37 clones examined, respectively, suggesting that creation of the initiation codon is a post-transcriptional event. The BamHI site at nucleotide position 757–762 within the coxI genomic DNA was altered in all 97 cDNA clones examined, demonstrating that RNA editing at this site in the transcripts is very common. RNA editing takes place to a lesser extent at the initiation codon, compared with editing at internal position 254. This indicates that editing is either a random process or that it involves a mechanism favoring less RNA editing in the initiation codon than in internal sites.
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  • 2
    ISSN: 1617-4623
    Keywords: Sugar beet ; nad9 ; Mitochondrial gene ; RNA editing
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract From a sugar beet mitochondrial DNA library, we have isolated an open reading frame (ORF192) showing extensive homology to the gene for the 30 kDa subunit of the bovine mitochondrial complex I (NADH:ubiquinone reductase). The ORF192 was found to be actively transcribed to give an RNA of approximately 1.0 kb. We have designated this gene nad9. Transcripts from the nad9 locus are edited by five C to U transitions, increasing similarity with the amino acid sequence of the corresponding bovine and Neurospora crassa polypeptides. Southern blot hybridization also indicates that nad9 is present in the mitochondrial genomes of a variety of higher plant species.
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  • 3
    ISSN: 1432-2242
    Keywords: Key words Nad4L-orf25 linkage ; RNA editing ; Sugar beet ; Mitochondria
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  We have found that a gene coding for NADH dehydrogenase subunit 4L and a presumed gene, orf25, are linked and co-transcribed with each other in sugar beet mitochondria. Ten and twelve C-to-U editing events were observed in the mRNAs of nad4L and orf25, respectively; the amino-acid sequence specified after editing is better-conserved in comparison with the homologues of other organisms. It is interesting to note that the translation initiation codon of nad4L is created by editing. The conservation of the nad4L-orf25 linkage was examined by PCR-amplification of the intergenic region. We obtained successful PCR products from five dicots (spinach, apple, snapdragon, petunia and tobacco) and two monocots (tulip and pineapple), but not in two poaceous plants, rice and maize. The intergenic region, when present, was found to be well-conserved in its sequence, suggesting a monophyletic origin of this linkage. Our result, together with previous reports of Arabidopsis and four poaceous species, favour the argument that the nad4L-orf25 linkage is conserved throughout angiosperms except in the Poaceae.
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  • 4
    ISSN: 1573-5028
    Keywords: group-II intron ; mitochondria ; ribosomal protein ; rice ; RNA editing
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The mitochondrial ribosomal protein L2 gene (rpl2) is coded by two exons of 840 and 669 bp separated by an intron sequence of 1481 bp in the rice mitochondrial genome. The rpl2 gene is located three nucleotides upstream of the ribosomal protein S19 gene (rps19) and both genes are co-transcribed. cDNA sequence analysis indentified splicing of the intron sequence from the rpl2 mRNA as well as RNA editing events. The deduced secondary structure of the rpl2 intron sequence shows the characteristic features of a group-II intron. A single RNA editing site is identified in rpl2 and six editing sites in rps19 transcripts. In addition, one editing site is observed in the 3 nucleotide intergenic region. Analysis of individual cDNA clones showed a different extent of RNA editing. The rice rpl2 intron is located at a different site and shows no significant nucleotide sequence similarity with the rpl2 intron of liverwort. However, 60% nucleotide sequence identity is observed between the rice rpl2 intron and the Oenothera nad5 intron in a 234 nucleotide region. The mitochondrial rpl2 sequence is absent from the pea mitochondrial genome and we consequently propose that the mitochondrial RPL2 protein is encoded by a nuclear gene in pea.
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  • 5
    ISSN: 1573-5028
    Keywords: motifs ; organelle ; polarity ; RNA editing ; specificity factor
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The RNA editing processes in chloroplasts and mitochondria of higher plants show several similarities which are suggestive of common components and/or biochemical steps between the two plant organelles. The existence of various promiscuous DNA fragments of chloroplast origin in plant mitochondrial genomes allowed us to test the possibility that chloroplast sequences are also edited in mitochondria. AnrpoB fragment transferred from chloroplasts to mitochondria in rice was chosen as it contains several editing sites, two of which match sequence motifs surrounding even non-homologous editing sites in both chloroplast and mitochondrial transcripts. Rice chloroplast and mitochondrialrpoB DNA and cDNA sequences were selectively amplified and the editing status of the cDNA sequences was determined. Three of the four potentialrpoB editing sites previously detected in maize were found to be edited in the rice chloroplastrpoB transcript, whereas the fourth was found to remain unedited. In mitochondria, however, all four editing sites remain unmodified at the cDNA level. This indicates that the editing processes of higher plant mitochondria and chloroplasts are not identical and that organelle-specific factors are required for eliciting the respective editing events.
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  • 6
    ISSN: 1572-8927
    Keywords: Hydrogen-1 ; nitrogen-15 ; chlorine-35 ; NMR coordination ; Lu(ClO4)3 ; Lu(NO3)3
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract A coordination study of Lu(III) has been carried out for the nitrate and perchlorate salts in aqueous mixtures of acetone-d6 and Freon-12 by1H,15N and35Cl NMR spectroscopy. At temperatures lower than −90°C, proton and ligand exchange are slow enough to permit the direct observation of1H resonance signals for coordinated and free water molecules, leading to an accurate measure of the Lu(III) hydration number. In perchlorate solution, in the absence of inner-shell ion-pairing, Lu(III) exhibits a maximum coordination number of six over the allowable concentration range of study, contrasting markedly with the report of values of six to nine or greater as determined by a similar NMR method. The absence of contact ion-pairing was confirmed by35Cl NMR chemical shift and linewidth measurements. Extensive ion-pairing was observed in the nitrate solutions as reflected by the lower Lu(III) hydration numbers of two to three in these systems, the observation of two coordinated water signals, and15N NMR signals for two complexes. The1H and15N NMR spectra and the hydration number could be accounted for by the presence of (H2O)4Lu(NO3)2+ and (H2O)2Lu(NO3) 2 1+ .
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  • 7
    ISSN: 1572-8927
    Keywords: Nitrogen-15 ; chlorine-35 ; NMR ; cerium nitrate ; complexation ; water acetone mixtures
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract A study of the complex formation which occurs between cerium(III) and nitrate ions in aqueous solvent mixtures has been carried out by a direct, low-temperature, nitrogen-15 (15N) NMR technique. At temperatures in the range of −95 to −110°C, ligand exchange is slow enough to permit the observation of separate15N NMR signals for bulk nitrate, and this anion in the cerium(III) principal coordination shell. In water-acetone-Freon-12 mixtures, the spectra reveal the nitrato complexes do not form consecutively. Rather, signals are observed for Ce(NO3)2+, Ce(NO3) 2 1+ , and only two other higher order complexes, even at very high NO 3 − to Ce(III) mole ratios. Signal area evaluations were used to identify the possible higher order complexes. At comparable salt concentrations in aqueous-methanol mixtures, only Ce(NO3)2+ and Ce(NO3) 2 1+ are formed, reflecting a decreased tendency for complexation in media of higher dielectric constant.
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  • 8
    ISSN: 1572-8927
    Keywords: Hydrogen-1 ; nitrogen-15 ; chlorine-35 ; NMR ; erbium nitrate ; complexation ; acetone ; methanol
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The extent of inner-shell ion-pair formation of Er3+ with nitrate ion in aqueous mixtures has been studied by nitrogen-15 (15N) NMR spectroscopy. At low temperature, exchange is slow enough to permit the direct observation of15N signals for nitrate ions in the Er3+ solvation shell and in bulk medium. In water-acetone mixtures,15N NMR signals for the mono-and bis complexes are observed at low nitrate to Er3+ mole ratios, but only the bis complex is evident at higher anion concentrations. No spectral evidence for the tris complex was seen at any nitrate concentration. In water-methanol-acetone mixtures, signals for the mono and bis complexes persist even at higher nitrate concentrations, indicating a reduced tendency to ion-pair with increasing dielectric constant. Preliminary15N NMR results are presented for the nitrate complexes of other paramagnetic lanthanide ions.
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  • 9
    ISSN: 1572-8927
    Keywords: Carbon-13 ; nitrogen-15 ; chlorine-35 ; NMR ; samarium(III) ; isothiocyanate ; Sm3+ − NCS− complexes ; water–acetone–Freon ; water–methanol
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Multinuclear magnetic resonance studies of trivalent lanthanide inner-shell ion-pairing with nitrate and isothiocyanate are continuing. For NCS− solutions in water–acetone–Freon mixtures at low temperature, generally −100 to −125°C, ligand exchange is slow enough to permit the observation of 13C and 15N NMR signals for coordinated and free anions. For samariuni(III) solutions, four coordinated NCS−signals, displaced about +35 ppm and +250 ppm from free anion, are observed in the 13C and 15N NMR spectra, respectively. The 13C and 15N NMR data are complementary, showing a signal area concentration dependence and measured coordination numbers consistent with the formation of Sm(NCS)2+ through Sm(NCS) 4 1 . The coordination numbers reach a maximum of about three moles of NCS− per mole of Sm(III) with both nuclides, a result confirmed by spectral appearance showing the dominance of Sm(NCS)3 at the highest concentration studied. An analysis of the chemical shifts indicates that binding occurs at the nitrogen atom of NCS−. In water–methanol, due to the higher dielectric constant of such mixtures, coordination was less extensive. A competitive binding study with Ci− by 35Ci NMR demonstrated conclusively the superior coordinating ability of NCS−.
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  • 10
    ISSN: 1572-8927
    Keywords: carbon-13 ; nitrogen-15 ; chlorine-35 ; NMR ; cerium(III)–isothiocyanate complexes ; water–acetone–Freon ; water–methanol
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract A study of lanthanide complexation with isothiocyanate is underway using a multinuclear magnetic resonance technique. For isothiocyanate solutions in water–acetone–Freon mixtures at low temperature, −85–−125°C, ligand exchange is slow enough to permit the observation of 13C and 15N NMR signals for coordinated and free anions. For the Ce3+–NCS− system, four coordinated anion signals, displaced from the free anion signal by about +450 to +550 ppm for 15N and +50 to +80 ppm for 13C, are observed. The 13C and 15N spectral data are complementary, showing a signal area concentration dependence and measured coordination numbers consistent with the formation of Ce(NCS)2+ through Ce(NCS)1- 4. In water–methanol, the extent of complexing is decreased, presumably because of the higher dielectric constant of this medium. In addition, the results of a competitive study of NCS− and Cl− ion binding, carried out using 35Cl NMR, is presented.
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