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Updated: Aug 12, 2026
11:27
Studying DNA Looping by Single-Molecule FRET
Published on: June 28, 2014
Mechanistic diversity of clamp loading at small DNA gaps
Fengwei Zheng1, Michael E O'Donnell2, Huilin Li1
1Department of Structural Biology, Van Andel Institute, Grand Rapids, Michigan, USA.
The Journal of Biological Chemistry
|August 10, 2026
Summary
DNA sliding clamps are crucial for DNA replication and repair. Specialized clamp loaders use distinct strategies to load these essential proteins onto various DNA structures, ensuring genome stability.
Area of Science:
- Molecular Biology
- Genetics
- Biochemistry
Background:
- DNA sliding clamps, like PCNA and the 9-1-1 complex, are vital ring-shaped proteins that encircle DNA.
- They act as platforms for DNA replication, repair, and checkpoint signaling.
- Loading mechanisms at standard DNA junctions are understood, but loading onto constrained intermediates like nicks and gaps remained unclear.
Purpose of the Study:
- To investigate the diverse strategies employed by clamp loaders for loading DNA sliding clamps onto geometrically constrained DNA intermediates.
- To elucidate how clamp loaders adapt to different DNA structures and cellular contexts.
Main Methods:
- Cryo-electron microscopy studies were utilized to visualize clamp loader-DNA interactions.
- Comparative analysis of different clamp loader complexes (e.g., RFC, DnaX, Rad24-RFC, Ctf18-RFC, Elg1-RFC) and their DNA binding and processing activities.
Main Results:
- Eukaryotic RFC loads PCNA onto gapped DNA by engaging both 3' and 5' ends and unwinding DNA.
- Bacterial DnaX and checkpoint Rad24-RFC load clamps onto small and large gaps, respectively, using DNA bending or lacking unwinding activity.
- Specialized loaders like Ctf18-RFC and Elg1-RFC are involved in leading-strand synthesis and PCNA unloading.
Conclusions:
- Clamp loaders exhibit remarkable diversity in their mechanisms to accommodate varying DNA structures and cellular roles.
- These specialized loading and unloading strategies are critical for precise control of genome replication and maintenance.
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