Sequence-Dependent Deviations of Constrained DNA from Canonical B-Form.

Area of Science:

• Biophysics
• Molecular Biology
• Structural Biology

Background:

• Canonical structural models of short DNA exist from crystallographic and NMR studies.
• In vivo, long DNA molecules face constraints from membranes, proteins, and other molecules, which cannot be tested by existing methods.
• Previous experimental methods lack the resolution to study DNA structure under biologically relevant constraints.

Purpose of the Study:

• To investigate the in vivo structure of long DNA molecules under biologically relevant constraints.
• To compare DNA structures under constrained conditions with canonical models.
• To highlight the utility of atomic force microscopy (AFM) for single-molecule DNA characterization.

Main Methods:

• High-resolution frequency-modulation atomic force microscopy (AFM).
• Imaging of single long DNA molecules: poly(dA)-poly(dT), poly(dG)-poly(dC), and lambda DNA.
• Utilizing an underlying substrate to emulate biological constraints on DNA structure.

Main Results:

• Observed systematic, sequence-dependent variations in DNA groove dimensions.
• Demonstrated that DNA structure under realistic interactions differs from canonical models.
• Showcased AFM's capability for single-molecule characterization of DNA under constraint.

Conclusions:

• The structure of DNA in a constrained, biologically relevant environment deviates from established canonical models.
• Atomic force microscopy (AFM) provides a unique tool for characterizing single DNA molecules under near-physiological conditions.
• Findings necessitate a re-evaluation of current DNA structural models in the context of cellular environments.