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Structure of plectonemically supercoiled DNA.

T C Boles1, J H White, N R Cozzarelli

  • 1Department of Molecular Biology, University of California, Berkeley 94720.

Journal of Molecular Biology
|June 20, 1990
PubMed
Summary
This summary is machine-generated.

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Negatively supercoiled circular DNA forms a branched, interwound structure in solution. This DNA structure, while not compacting well, may facilitate interactions between distant DNA sequences.

Area of Science:

  • Structural Biology
  • Molecular Biophysics
  • Genomics

Background:

  • DNA supercoiling is a critical factor influencing DNA structure and function.
  • Understanding the three-dimensional structure of supercoiled DNA is essential for comprehending gene regulation and replication.
  • Previous studies have provided insights into DNA supercoiling, but an average solution structure remains to be fully elucidated.

Purpose of the Study:

  • To determine the average three-dimensional structure of negatively supercoiled circular DNA in solution.
  • To investigate the relationship between DNA supercoiling, structural parameters, and flexibility.
  • To explore the biological implications of the deduced DNA structure.

Main Methods:

  • Electron microscopy was employed to visualize DNA structures.

Related Experiment Videos

  • Topological methods were utilized for structural analysis and parameter quantification.
  • Computational analysis was performed to calculate DNA flexibility constants.

    • Main Results:

    • Negatively supercoiled DNA adopts a branched, plectonemic (interwound) conformation.
    • The superhelix axis length remained constant at 41% of DNA length, while radius decreased hyperbolically with increasing supercoiling.
    • The number of supercoils was found to be 89% of the linking deficit, with a fixed ratio of writhe to twist change (2.6:1).
    • Branching of the superhelix axis correlated with plasmid length but not superhelix density.

    Conclusions:

    • The determined DNA structure provides a detailed average model for supercoiled DNA in solution.
    • The structural findings suggest that while this form offers limited compaction, it may enhance interactions between distant DNA elements.
    • The study offers valuable insights into DNA structural dynamics and their potential roles in biological processes.