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Related Experiment Videos

Dimeric lac repressors exhibit phase-dependent co-operativity

J Müller1, A Barker, S Oehler

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

Journal of Molecular Biology
|December 5, 1998
PubMed
Summary

Even dimeric Lac repressor (LacR) can repress the lac operon, showing DNA helical repeat dependence. This residual repression relies on the operator O1 and the repressor's C-terminus.

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Area of Science:

  • Molecular Biology
  • Genetics
  • Biochemistry

Background:

  • Lac repressor (LacR) binding to the lac operator (O1) represses transcription in Escherichia coli.
  • Full repression by tetrameric LacR requires auxiliary operators (O2, O3) positioned correctly on the DNA helix.
  • Dimeric LacR mutants show reduced repression, comparable to tetrameric LacR without auxiliary operators.

Purpose of the Study:

  • Investigate residual repression by dimeric LacR on constructs with O1 and an auxiliary operator (Oid).
  • Determine if dimeric LacR-mediated repression exhibits phase dependence related to DNA helical structure.
  • Explore the role of the LacR C-terminus in residual repression.

Main Methods:

  • Utilized constructs with a CAP-independent promoter, O1, and Oid separated by variable spacers.

Related Experiment Videos

  • Assessed repression by dimeric LacR variants with altered C-termini.
  • Performed control experiments to confirm the necessity of O1 for repression.

    • Main Results:

    • Dimeric LacR-mediated repression showed surprising phase dependence, correlating with DNA helical repeat.
    • Repression magnitude was lower than with tetrameric LacR but still exhibited periodicity.
    • The C-terminal region's basic nature correlated with repression maxima, suggesting weak DNA contacts.
    • Operator O1 was essential for repression; auxiliary operator binding alone was insufficient.

    Conclusions:

    • Dimeric LacR retains residual repression capabilities with phase dependence, indicating structural memory of DNA helical repeat.
    • Weak, non-specific interactions involving the LacR C-terminus likely contribute to this periodicity.
    • Further investigation is needed to identify potential additional factors involved in residual repression.