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Related Experiment Videos

Sequestration stabilizes lac repressor-DNA complexes during gel electrophoresis

K M Vossen1, M G Fried

  • 1Department of Biochemistry and Molecular Biology, Pennsylvania State University College of Medicine, Hershey 17033, USA.

Analytical Biochemistry
|February 1, 1997
PubMed
Summary

Protein-DNA complexes, like the E. coli lac repressor and DNA, stay stable longer in gels than in solution. This stabilization in gels is likely due to reduced encounter frequency, not gel interactions.

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Area of Science:

  • Biochemistry
  • Molecular Biology
  • Biophysics

Background:

  • Gel electrophoresis mobility shift assays (EMSAs) are crucial for studying protein-nucleic acid interactions.
  • Protein-nucleic acid complexes often exhibit prolonged stability within gels compared to their solution lifetimes.
  • Proposed mechanisms for this enhanced stability include excluded volume and matrix-interaction effects.

Purpose of the Study:

  • To investigate the influence of gel composition and concentration on the dissociation kinetics of protein-DNA complexes.
  • To differentiate between excluded volume and matrix-interaction mechanisms for complex stabilization in gels.
  • To analyze the dissociation rates of the Escherichia coli lactose (lac) repressor protein and lactose promoter DNA complexes.

Main Methods:

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  • Utilized gel electrophoresis mobility shift assays (EMSAs) to study protein-DNA complex dissociation.
  • Examined dissociation kinetics in both polyacrylamide and agarose gels of varying concentrations.
  • Measured pseudo first-order dissociation rates (kdiss) under different conditions.

    • Main Results:

    • Dissociation rates of lac repressor-DNA complexes were slower in gels than in free solution.
    • Dissociation rates decreased with increasing gel concentration for both polyacrylamide and agarose gels.
    • In free solution, kdiss was proportional to [DNA]^0.83, while in 10% polyacrylamide, kdiss was proportional to [DNA]^0.48.

    Conclusions:

    • The observed stabilization in gels is inconsistent with specific matrix-interaction mechanisms.
    • Results suggest that reduced encounter frequency limits complex lifetimes in free solution.
    • Stabilization in gels may arise from a decrease in encounter frequency between DNA molecules or protein-DNA complexes.