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Analysis of the intrinsic bend in the M13 origin of replication by atomic force microscopy
Yongjun Lu1, Brock D Weers, Nancy C Stellwagen
1Department of Biochemistry, University of Iowa, Iowa City, Iowa 52242, USA.
Abstract:
Atomic force microscopy (AFM) has been used to image a 471-bp bent DNA restriction fragment derived from the M13 origin of replication in plasmid LITMUS 28, and a 476-bp normal, unbent fragment from plasmid pUC19. The most probable angle of curvature of the 471-bp DNA fragment is 40-50 degrees, in reasonably good agreement with the bend angle determined by transient electric birefringence, 38 degrees +/- 7 degrees. The normal 476-bp DNA fragment exhibited a Gaussian distribution of bend angles centered at 0 degrees, indicating that this fragment does not contain an intrinsic bend. The persistence length, P, was estimated to be 60 +/- 8 and 62 +/- 8 nm for the 471- and 476-bp fragments, respectively, from the observed mean-square end-to-end distances in the AFM images. Since the P-values of the normal and bent fragments are close to each other, the overall flexibility of DNA fragments of this size is only marginally affected by the presence of a stable bend. The close agreement of AFM and transient electric birefringence results validates the suitability of both methods for characterizing DNA bending and flexibility.
Insights
Atomic force microscopy (AFM) revealed DNA bending angles in a 471-bp fragment, aligning with transient electric birefringence. DNA flexibility was minimally impacted by the stable bend.
Area of Science:
- Biophysics
- Molecular Biology
- Nanotechnology
Background:
- DNA structure and dynamics are crucial for biological processes.
- Quantifying DNA bending and flexibility is essential for understanding DNA-protein interactions and gene regulation.
Purpose of the Study:
- To investigate and compare DNA bending angles and flexibility using Atomic Force Microscopy (AFM) and transient electric birefringence.
- To characterize a naturally bent DNA fragment and a normal DNA fragment.
Main Methods:
- Atomic Force Microscopy (AFM) was employed to image DNA fragments.
- Transient electric birefringence was used to determine DNA bend angles.
- Persistence length was calculated from AFM images.
Main Results:
- AFM imaging determined a probable bend angle of 40-50 degrees for the 471-bp bent DNA fragment.
- The bent DNA fragment's bend angle closely agreed with transient electric birefringence results (38° ± 7°).
- Persistence length measurements indicated that DNA flexibility is only marginally affected by a stable bend.
Conclusions:
- AFM is a suitable method for characterizing DNA bending and flexibility.
- The findings validate the use of both AFM and transient electric birefringence for DNA structural analysis.
- Stable DNA bends have minimal impact on the overall flexibility of DNA fragments of this size.