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  • 1
    Electronic Resource
    Electronic Resource
    Relaxation of supercoiled DNA associated with induction of heat shock proteins in Escherichia coli (1993)
    Springer
    Molecular genetics and genomics 238 (1993), S. 1-5 
    Details
    ISSN: 1617-4623
    Keywords: DNA relaxation ; DNA supercoiling ; DNA gyrase ; Heat shock response ; rpoH
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Heat treatment of wild-type Escherichia coli cells led to a transient relaxation of negatively supercoiled plasmid DNA and there was no recovery of DNA torsional strain in the DNA in gyrA mutant cells. After heat treatment, DnaK and GroEL proteins were synthesized continuously in the gyrA mutant cells, whereas they were synthesized only transiently in wild-type cells. Thus, change in superhelical density of the DNA correlated with the temperature-induced expression of heat shock proteins. Inhibitors of DNA gyrase (nalidixic acid, novobiocin), an organic solvent (ethanol) and a psychotropic drug (chlorpromazine) all stimulated relaxation of cellular DNA over the same concentration range that induces heat shock proteins. As DNA relaxation was induced by heat treatment or chemicals in an rpoH mutant, the process is not the result of induced synthesis of heat shock proteins.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00279523
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Co-induction of DNA relaxation and synthesis of DnaK and GroEL proteins inEscherichia coli by expression of LetD (CcdB) protein, an inhibitor of DNA gyrase encoded by the F factor (1996)
    Springer
    Molecular genetics and genomics 250 (1996), S. 593-600 
    Details
    ISSN: 1617-4623
    Keywords: DNA relaxation ; Heat shock response ; LetD (CcdB) protein ; DNA gyrase ; σ 32
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract We examined the influence of overexpression of LetD (CcdB) protein, an inhibitor of DNA gyrase encoded by the F factor ofEscherichia coli, on DNA supercoiling and induction of heat shock proteins. Cells were transformed with a plasmid carrying the structural gene for LetD protein under control of thetac promoter, and LetD protein was induced by adding isopropylβ-d-thiogalactopyranoside (IPTG) to the culture medium. Analysis by agarose gel electrophoresis in the presence of chloroquine revealed relaxation of plasmid DNA in cells depending on the concentration of IPTG employed for induction. Protein pulse-labeling experiments with [35S]methionine and cysteine revealed that synthesis of DnaK and GroEL proteins was also induced by IPTG, and concentrations necessary for DNA relaxation and induction of the heat shock proteins were much the same. Expression of mutant LetD protein lacking two amino acid residues at the C-terminus induced neither DNA relaxation nor the synthesis of DnaK and GroEL proteins. Induction of wild-type LetD protein but not mutant LetD protein markedly enhanced synthesis ofσ 32. We interpret these results to mean that DNA relaxation in cells caused by the expression of LetD protein induces heat shock proteins via increased synthesis ofσ 32.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02174447
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Identification of DNA topoisomerases involved in immediate and transient DNA relaxation induced by heat shock inEscherichia coli (1994)
    Springer
    Molecular genetics and genomics 244 (1994), S. 451-455 
    Details
    ISSN: 1617-4623
    Keywords: Heat shock ; DNA relaxation ; topA ; DNA topoisomerase I ; DNA gyrase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The linking number of plasmid DNA in exponentially growingEscherichia coli increases immediately and transiently after heat shock. The purpose of this study was to search for DNA topoisomerases that catalyze this relaxation of DNA. Neither introduction of atopA deletion mutation nor treatment of cells with DNA gyrase inhibitors affected the DNA relaxation induced by heat shock. Thus, DNA topoisomerase I and DNA gyrase are apparently not involved in the process. However, the reaction was inhibited by nalidixic acid or by oxolinic acid in thetopA mutant and the reaction was resistant to nalidixic acid in atopA mutant carrying, in addition, thenalA26 mutation. These results are interpreted as indicating that both DNA topoisomerase I and DNA gyrase are involved in the DNA relaxation induced by heat shock.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00583895
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    Paper (German National Licenses)
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