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Related Experiment Videos

A structural transition in d(AT)n.d(AT)n inserts within superhelical DNA.

I Panyutin1, V Lyamichev, S Mirkin

  • 1Institute of Molecular Genetics, USSR Academy of Sciences, Moscow.

Journal of Biomolecular Structure & Dynamics
|June 1, 1985
PubMed
Summary

Researchers studied DNA structural transitions in d(AT)n.d(AT)n sequences. Findings suggest these sequences form a cruciform structure, not the Z-form, when supercoiled, with implications for DNA topology.

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Area of Science:

  • Molecular Biology
  • Biochemistry
  • Structural Biology

Background:

  • DNA supercoiling is crucial for genome organization and function.
  • Specific DNA sequences can adopt non-canonical structures under topological stress.
  • The d(AT)n.d(AT)n sequence is known for its potential to form unusual structures.

Purpose of the Study:

  • To investigate the structural transitions of d(AT)n.d(AT)n inserts in plasmids under varying superhelicity.
  • To determine whether these inserts adopt a cruciform or Z-form structure.
  • To understand the relationship between superhelical stress and DNA structural changes.

Main Methods:

  • Construction of plasmids with varying lengths of d(AT)n.d(AT)n inserts.
  • Two-dimensional gel electrophoresis to analyze DNA topoisomers and structural transitions.

Related Experiment Videos

  • Enzymatic cleavage using single-strand-specific endonuclease S1.
  • Kinetic studies to support structural characterization.

    • Main Results:

    • Increased negative superhelicity induced a structural transition in d(AT)n.d(AT)n inserts, reducing superhelical stress.
    • The observed stress reduction did not match theoretical values for cruciform or Z-form DNA.
    • Endonuclease S1 specifically cleaved DNA topoisomers exhibiting the structural transition at the insert's center.
    • Kinetic data and S1 cleavage patterns indicated a cruciform structure.

    Conclusions:

    • Cloned d(AT)n.d(AT)n sequences adopt a cruciform structure rather than the Z-form under superhelical stress.
    • A discrepancy exists between the observed and expected superhelical stress release for cruciform formation.
    • Further investigation is needed to explain the observed stress release values in cruciform structures.