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Related Experiment Videos

Supercoiling facilitates lac operator-repressor-pseudooperator interactions.

P A Whitson, W T Hsieh, R D Wells

    The Journal of Biological Chemistry
    |April 15, 1987
    PubMed
    Summary
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    Negative supercoiling of DNA enhances the binding affinity of the Escherichia coli lactose repressor to operator DNA. DNA topology and pseudooperators play a critical role in regulating the lac operon in vivo.

    Area of Science:

    • Molecular Biology
    • Biochemistry
    • Genetics

    Background:

    • The lactose repressor (LacI) protein regulates the lac operon in Escherichia coli.
    • DNA topology, specifically supercoiling, is known to influence protein-DNA interactions.

    Purpose of the Study:

    • To investigate the effect of DNA negative supercoiling on the binding affinity of the lactose repressor to operator DNA.
    • To determine the role of DNA topology and pseudooperator sequences in the regulation of the lac operon.

    Main Methods:

    • Assessing binding affinity and dissociation rates of the lactose repressor to supercoiled and linear plasmids containing operator sequences.
    • Quantifying ionic interactions in protein-DNA complexes.

    Main Results:

    Related Experiment Videos

    • Negative supercoiling significantly increased the binding affinity of the lactose repressor to operator-containing plasmids.
    • Dissociation rates decreased with increasing negative supercoil density, especially in the presence of pseudooperator sequences.
    • Supercoiling and multiple operator sites stabilized ternary complexes, suggesting a looped structure.

    Conclusions:

    • DNA topology, particularly negative supercoiling, is a critical factor in modulating lactose repressor-operator interactions.
    • Pseudooperator sequences enhance the stability of repressor-DNA complexes under supercoiling conditions.
    • These findings highlight the in vivo importance of DNA topology and pseudooperators in transcriptional regulation of the lac operon.