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Related Experiment Videos

Structural recognition and distortion by the DNA junction-resolving enzyme RusA

M J Giraud-Panis1, D M Lilley

  • 1Department of Biochemistry, The University of Dundee, Dundee, DD1 4HN, UK.

Journal of Molecular Biology
|May 26, 1998
PubMed
Summary

The RusA enzyme, a DNA junction-resolving protein, binds and distorts DNA structures. This enzyme specifically cleaves DNA at a CpC sequence, with a key aspartate residue crucial for its function.

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Area of Science:

  • Biochemistry
  • Molecular Biology
  • Structural Biology

Background:

  • RusA is a DNA junction-resolving enzyme from lambdoid phages.
  • It shares similarities with other junction-resolving enzymes.
  • RusA functions as a dimer and binds DNA junctions with high affinity.

Purpose of the Study:

  • To characterize the biochemical and structural properties of the RusA enzyme.
  • To investigate the mechanism of DNA cleavage by RusA.
  • To identify key residues involved in RusA's enzymatic activity.

Main Methods:

  • Dimeric binding analysis (dissociation constant, subunit exchange).
  • Cleavage assays on fixed and mobile DNA junctions.
  • Site-directed mutagenesis to create RusA D70N mutant.

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  • Comparative gel electrophoresis to analyze DNA junction structure.

    • Main Results:

    • RusA binds DNA junctions as a dimer (Kd 2-7 nM) and exists as a dimer in solution.
    • The enzyme prefers cleaving DNA 5' to a CpC sequence.
    • RusA D70N mutant binds DNA but shows no cleavage activity, highlighting Aspartate 70's role.
    • Cleavage rate decreases when DNA junction conformation is constrained.
    • RusA binding alters the global structure of DNA junctions, independent of magnesium ions.

    Conclusions:

    • RusA recognizes and distorts DNA junction structures for resolution.
    • Aspartate 70 is critical for the catalytic cleavage activity of RusA.
    • The enzyme's mechanism involves conformational changes in the DNA substrate.