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The MukB-ParC interaction affects the intramolecular, not intermolecular, activities of topoisomerase IV

Ryo Hayama1, Soon Bahng2, Mehmet E Karasu3

  • 1Physiology, Biophysics, and Systems Biology Graduate Program, Weill Cornell Graduate School of Medical Sciences, New York, New York 10065.

The Journal of Biological Chemistry
|January 26, 2013
PubMed

Insights

The bacterial condensin MukB interacts with topoisomerase IV, aiding DNA relaxation and knotting. This interaction appears crucial for chromosome organization, not daughter chromosome segregation.

Area of Science:

  • Molecular Biology
  • Genetics
  • Biochemistry

Background:

  • Chromosome organization relies on proteins like condensins and topoisomerases to manage DNA structure and topology.
  • Condensins shape DNA, while topoisomerases modulate DNA topology through various enzymatic activities.
  • Understanding protein interactions is key to elucidating mechanisms of chromosome management.

Purpose of the Study:

  • To investigate the functional interaction between MukB, a bacterial condensin, and ParC, a subunit of topoisomerase IV.
  • To determine the role of this interaction in DNA topological rearrangements, including relaxation, knotting, and decatenation.
  • To ascertain whether the MukB-ParC interaction contributes to chromosome organization or daughter chromosome segregation.

Main Methods:

  • Biochemical assays measuring DNA relaxation, knotting, and decatenation activities of topoisomerase IV.
  • Assessment of topoisomerase IV activity in the presence and absence of MukB.
  • Investigation of MukB's DNA binding requirements and the effect of DNA supercoiling chirality on the interaction.

Main Results:

  • The interaction between MukB and ParC significantly enhanced the relaxation of negatively supercoiled DNA by topoisomerase IV.
  • MukB-ParC interaction also promoted topoisomerase IV-mediated knotting of DNA, an intramolecular rearrangement.
  • Decatenation of multiply linked DNA dimers, an intermolecular rearrangement essential for chromosome segregation, was not enhanced by the MukB-ParC interaction.
  • MukB DNA binding and a specific chiral DNA arrangement were necessary for stimulating topoisomerase IV activity, as relaxation of positively supercoiled DNA was unaffected.

Conclusions:

  • The MukB-ParC interaction facilitates topological reconfiguration of negatively supercoiled DNA, suggesting a role in chromosome organization.
  • The observed effects indicate that this interaction is more likely involved in structuring chromosomes rather than in the separation of daughter chromosomes.
  • These findings provide insights into the specialized roles of protein complexes in managing complex DNA topologies within bacterial cells.

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