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  • 1
    Electronic Resource
    Electronic Resource
    Post-transcriptional enhancement of Escherichia coli bgl operon silencing by limitation of BglG-mediated antitermination at low transcription rates (2002)
    Oxford, UK : Blackwell Science Ltd.
    Molecular microbiology 43 (2002), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The silent bgl operon of Escherichia coli is activated by spontaneous mutations that derepress its promoter. In addition, expression depends on specific transcriptional antitermination within the operon by the antiterminator protein BglG. Here, we show that BglG-mediated antitermination limits expression of the bgl operon when the cellular transcription rate is low. The expression levels of chromosomally encoded activated bgl operon alleles are low but increase significantly when BglG protein is provided in trans or when the expression is rendered inde-pendent of BglG-mediated antitermination by mutation of the terminator. Plasmid-encoded activated bgl operon alleles are expressed at high levels. Moreover, a moderate (threefold) further increase in the transcription rate of chromosomally encoded activated bgl operon alleles in an rpoS mutant can result in high (up to 50-fold increased) expression levels. These data show that the expression of the bgl operon does not correlate linearly with its cellular transcription rate. Moderate differences in the transcription initiation rate are amplified post-transcriptionally into large changes in the expression level of the operon by the requirement of a threshold for BglG-mediated antitermination. Implications for bgl operon regulation by global regulators H-NS, RpoS and others are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2958.2002.02734.x
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  • 2
    Electronic Resource
    Electronic Resource
    The histone-like nucleoid structuring protein H-NS represses the Escherichia coli bgl operon downstream of the promoter (2004)
    Oxford, UK : Blackwell Science Ltd
    Molecular microbiology 52 (2004), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Specificity of repression by the histone-like nucleoid structuring protein and pleiotropic regulator, H-NS, is exceptionally high in case of the Escherichia coli bgl (β-glucoside) operon. Here we present evidence that H-NS represses the operon at two levels. The binding of H-NS to an upstream silencer results in an ∼threefold repression of the catabolite gene regulator protein (CRP) dependent bgl promoter. In addition, H-NS binds to a silencer region located approximately 600–700 base pairs downstream of the promoter, within the coding region of first gene, bglG, resulting in a ∼sevenfold further decrease of expression. Repression by H-NS at the downstream silencer requires termination factor Rho and is reduced by translation of the bglG mRNA, but is independent of the promoter. This suggests that H-NS induces polarity of transcription by acting as a roadblock to the elongat-ing RNA polymerase. The control of the bgl operon by H-NS at two levels results in a highly specific repression.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2958.2004.04001.x
    Library Location Call Number Volume/Issue/Year Availability
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    Paper (German National Licenses)
    Fulltext
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