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DNA strand arrangement within the SfiI-DNA complex: atomic force microscopy analysis.
Alexander Y Lushnikov1, Vladimir N Potaman, Elena A Oussatcheva
1Department of Pharmaceutical Sciences, College of Pharmacy, University of Nebraska Medical Center, Omaha, Nebraska 68198-6025, USA.
Biochemistry
|January 4, 2006
Summary
The SfiI restriction enzyme forms crossed DNA complexes, visualized using atomic force microscopy. DNA recognition sites within the complex exhibit specific angles, indicating no sequence preference in the central binding region.
Area of Science:
- Molecular Biology
- Structural Biology
- Biophysics
Background:
- The SfiI restriction enzyme functions as a tetramer, bridging two DNA recognition sites for cleavage.
- Understanding the SfiI-DNA complex structure is crucial for its application in molecular biology.
Purpose of the Study:
- To elucidate the structural properties of the SfiI-DNA complex using atomic force microscopy (AFM).
- To analyze the DNA path and orientation within SfiI-DNA complexes under non-cleaving conditions.
Main Methods:
- Atomic force microscopy (AFM) imaging of SfiI-DNA complexes under non-cleaving conditions (Ca2+ buffer).
- Analysis of intramolecular (cis) and intermolecular (trans) complexes.
- Systematic analysis of angles between DNA helices and design of DNA molecules with varying arm lengths.
Main Results:
- AFM imaging revealed tall spherical blobs at DNA intersections, identifying SfiI-DNA complexes.
- Analysis of DNA helix angles showed bimodal distributions around 60 and 120 degrees.
- Experiments with engineered DNA molecules confirmed that SfiI-DNA recognition sites are crossed, not bent.
Conclusions:
- The SfiI-DNA complex features crossed DNA recognition sites, with specific angular arrangements.
- The enzyme forms complexes with two possible helix orientations almost equally, suggesting weak sequence-specific contacts in the central DNA region.