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  • 1
    Electronic Resource
    Electronic Resource
    Is higher-order structure conserved in eukaryotic ribosomal DNA intergenic spacers? (1992)
    Springer
    Journal of molecular evolution 35 (1992), S. 514-523 
    Details
    ISSN: 1432-1432
    Keywords: Ribosomal RNA ; Intergenic spacer ; Secondary structure ; Chromatin organization ; Mosquito
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Computer-based structural analysis of the ribosomal DNA intergenic spacer (IGS) from the mosquito Aedes albopictus revealed a potential to form strong and extensive secondary structures throughout a 4.7-kilobase (kb) region. The predicted stability of secondary structures was particularly high within a 3.15-kb region containing 17 tandem 201 base-pair subrepeats. Similarly strong secondary structure potential was also found when IGS subrepeats were analyzed from 17 phylogenetically diverse eukaryotes, including vertebrates, invertebrates, and plants. Conservation of higher-order structure potential in the IGS region of ribosomal DNA may reflect evolutionary and functional constraints on chromatin organization, transcriptional regulation of the ribosomal RNA genes, and/or transcript processing and stability.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00160212
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  • 2
    Electronic Resource
    Electronic Resource
    Alfalfa (Medicago sativa L.) resistance to the root-lesion nematode, Pratylenchus penetrans: defense-response gene mRNA and isoflavonoid phytoalexin levels in roots (1998)
    Springer
    Plant molecular biology 38 (1998), S. 999-1010 
    Details
    ISSN: 1573-5028
    Keywords: chitinase ; disease resistance ; glucanase ; isoflavonoids ; mRNA ; phytoalexins
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Alfalfa (Medicago sativa) varieties with antibiosis-based resistance to the root-lesion nematode (Pratylenchus penetrans), a migratory endoparasite of many crops, have been developed by recurrent selection. Individual plants from these varieties that support significantly lower nematode reproduction were identified for molecular and biochemical characterization of defense responses. Before nematode infection, RNA blot analysis revealed 1.3–1.8-fold higher phenylpropanoid pathway mRNA levels in roots of three resistant plants as compared to three susceptible alfalfa plants. The mRNAs encoded the first enzyme in the pathway (phenylalanine ammonia-lyase), the first in the pathway branch for flavonoid biosynthesis (chalcone synthase), a key enzyme in medicarpin biosynthesis (isoflavone reductase) and a key enzyme in the pathway branch for biosynthesis of lignin cell wall precursors (caffeic acid O-methyltransferase). After nematode infection, the mRNAs declined over 48 h in resistant roots but rose in susceptible plants during the first 12 h after-infection and then declined. Acidic β-1,3-glucanase mRNA levels were initially similar in both root types but accumulated more rapidly in resistant than in susceptible roots after nematode infection. Levels of a class I chitinase mRNA were similar in both root types. Histone H3.2 mRNA levels, initially 1.3-fold higher in resistant roots, declined over 6–12 h to levels found in susceptible roots and remained stable in both root types thereafter. Defense-response gene transcripts in roots of nematode-resistant and susceptible alfalfa plants thus differed both constitutively and in inductive responses to nematode infection. HPLC analysis of isoflavonoid-derived metabolites of the phenylpropanoid pathway revealed similar total constitutive levels, but varying relative proportions and types, in roots of the resistant and susceptible plants. Nematode infection had no effect on isoflavonoid levels. Constitutive levels of the phytoalexin medicarpin were highest in roots of the two most resistant plants. Medicarpin inhibited motility of P. penetrans in vitro.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1006182908528
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  • 3
    Electronic Resource
    Electronic Resource
    Promoter utilization in a mosquito ribosomal DNA cistron (1995)
    New York, NY [u.a.] : Wiley-Blackwell
    Archives of Insect Biochemistry and Physiology 28 (1995), S. 143-157 
    Details
    ISSN: 0739-4462
    Keywords: mosquito ; A. albopictus ; cultured cells ; transcription ; promoter ; RNA polymerase I ; Chemistry ; Food Science, Agricultural, Medicinal and Pharmaceutical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology
    Notes: In the mosquito Aedes albopictus, two potential RNA polymerase I promoters that map 531 and 143 nucleotides upstream of the 18S rRNA gene have been defined on the basis of sequence homology with rRNA promoters from other species. Using the polymerase chain reaction, we confirmed that a 717 nucleotide region spanning the upstream (-531) and downstream (-143) promoters is homogeneous in genomic DNA and in cloned DNA. DNA probes representing each of these promoters, as well as upstream “spacer” promoters, exhibited protein-binding activity, and each unlabeled probe was an effective competitor of protein binding with the other probes, suggesting that these potential regulatory sequences interact with a common protein(s). Analysis of precursor ribosomal RNAs accumulated during temperature shock indicated that transcription is initiated primarily at the upstream (-531) promoter. RNAse protection and primer extension analyses confirmed the predominant use of this promoter, both in cultured cells and in mosquito life stages. © 1995 Wiley-Liss, Inc.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/arch.940280205
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    Paper (German National Licenses)
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