Related Experiment Videos
Structure of a RecA-DNA complex from linear dichroism and small-angle neutron-scattering in flow-oriented solution
B Nordén1, C Elvingson, T Eriksson
1Department of Physical Chemistry, Chalmers University of Technology, Gothenburg, Sweden.
Journal of Molecular Biology
|November 20, 1990
Summary
Small-angle neutron-scattering and ultraviolet linear dichroism reveal RecA-double-stranded DNA complex structure. The double-stranded DNA remains largely unperturbed within the RecA fiber, with bases oriented perpendicularly to the helix axis.
Area of Science:
- Biophysics
- Structural Biology
- Molecular Biophysics
Background:
- RecA protein plays a crucial role in DNA repair and recombination.
- Understanding the structural organization of RecA-dsDNA complexes is vital for elucidating its biological functions.
- Previous studies have investigated RecA interactions with both single-stranded and double-stranded DNA, but detailed structural insights remain limited.
Purpose of the Study:
- To determine the structural arrangement of double-stranded DNA (dsDNA) within a complex formed with the RecA protein.
- To investigate the orientation of DNA bases relative to the RecA polymer fiber.
- To compare the structural behavior of dsDNA in complex with RecA to that of single-stranded DNA.
Main Methods:
- Small-angle neutron-scattering (SANS) was employed to analyze the overall fiber orientation and structure.
- Ultraviolet linear dichroism (l.d.) was used to probe the orientation of DNA bases.
- Samples were aligned using flow in Couette devices made of neutron-transparent (niobium) and UV-transparent (silica) materials.
Main Results:
- SANS anisotropy indicated a modest orientation of the RecA-dsDNA fiber with the helix axis parallel to the flow field.
- Correlation with l.d. data inferred that DNA bases are oriented approximately perpendicular to the helix axis.
- The observed orientation of dsDNA was significantly better than that of single-stranded DNA in RecA complexes, suggesting dsDNA remains largely unperturbed.
Conclusions:
- The double-stranded DNA in the RecA complex is likely accommodated as a straight, unperturbed double helix aligned along the RecA polymer fiber.
- The DNA bases are oriented roughly perpendicular to the dsDNA helix axis.
- These findings suggest that RecA does not significantly strand separate the double-stranded DNA during complex formation, unlike its interaction with single-stranded DNA.