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Related Experiment Videos

Operator search by mutant Lac repressors

A Barker1, R Fickert, S Oehler

  • 1Institut für Genetik der Universität zu Köln, Köln, Weyertal 121, D-50931, Germany.

Journal of Molecular Biology
|June 20, 1998
PubMed
Summary

Bacterial repressors like LacR and GalR control gene expression. Tetrameric LacR variants with broader DNA binding showed reduced DNA association, unlike dimeric versions, influencing repression efficiency and evolution.

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Area of Science:

  • Molecular Biology
  • Genetics
  • Biochemistry

Background:

  • Escherichia coli LacR and GalR repressors belong to a homologous family of bacterial repressors.
  • Efficient gene repression requires specific DNA binding near the transcriptional start site.
  • LacR functions as a homotetramer, while GalR functions as a homodimer.

Purpose of the Study:

  • To investigate the functional implications of tetrameric vs. dimeric structures in DNA-binding specificity.
  • To understand the evolutionary divergence between LacR and GalR.

Main Methods:

  • Studied a LacR variant (LacR-V17A18) engineered to mimic GalR's DNA-binding specificity.
  • Assessed DNA-binding association rates of tetrameric and dimeric forms of wild-type and variant LacR on long DNA molecules.

Related Experiment Videos

  • Correlated in vitro binding kinetics with in vivo gene repression efficiency.

    • Main Results:

    • Tetrameric LacR variants with broadened specificity exhibited a 30-fold decrease in DNA association rate compared to wild-type LacR.
    • Dimeric versions of these variants showed unaltered association rates compared to dimeric wild-type LacR.
    • In vivo repression efficiency of lacZ correlated with the in vitro association rates, favoring dimers with broader specificity.

    Conclusions:

    • Stable homotetramer formation is disadvantageous for repression unless high DNA-binding specificity is present.
    • This functional constraint likely influenced the evolution of the LacI-GalR repressor family, favoring homodimers with broader DNA-binding specificities.