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The cofactor ATP in DNA-RecA complexes is not intercalated between DNA bases
1Groupe d'Etude Mutagénèse et Cancérogénèse, URA 1342 CNRS, Université Paris Sud, Orsay, France.
Journal of Molecular Recognition : JMR
|September 1, 1994
Summary
This study investigated how ATP analogs, adenosine 5'-O-(3-thiotriphosphate) (ATP gamma S) and guanosine 5'-O-(3-thiotriphosphate) (GTP gamma S), orient within RecA-DNA complexes. Results show cofactors are not intercalated between DNA bases, clarifying their role in DNA repair protein interactions.
Area of Science:
- Molecular Biology
- Biophysics
Background:
- RecA protein is crucial for DNA repair.
- ATP acts as a cofactor in RecA-DNA interactions.
- The precise orientation of cofactors within RecA-DNA complexes is not fully understood.
Purpose of the Study:
- To determine the orientation of ATP analogs (ATP gamma S and GTP gamma S) within RecA-DNA complexes.
- To investigate whether cofactors intercalate between DNA bases.
Main Methods:
- Flow linear dichroism spectroscopy was used to study RecA-DNA complexes with cofactor analogs.
- DNA base orientation was probed using poly(d epsilon A) dichroism.
- Spectra differences in the shorter-wavelength region revealed cofactor chromophore orientations.
Main Results:
- Both ATP gamma S and GTP gamma S promote RecA-DNA complexes with similar DNA base orientations.
- The guanine plane of GTP gamma S is oriented parallel to the complex's principal axis, not perpendicular like DNA bases.
- The adenine base of ATP gamma S also shows an orientation inconsistent with intercalation.
Conclusions:
- Cofactors like ATP gamma S and GTP gamma S are not intercalated between DNA bases in RecA-DNA complexes.
- This finding excludes a previously speculated model of cofactor binding.
- The study clarifies the role of ATP as a cofactor in RecA-DNA interactions.