Clamp Loader Dynamics in DNA Replication
Summary
The process of DNA replication relies on the coordinated action of a ring‐shaped sliding clamp and its specialised loader complexes. Sliding clamps, typified by proliferating cell nuclear antigen (PCNA) in eukaryotes, encircle DNA to tether polymerases and accessory factors, ensuring rapid and processive synthesis. Clamp loaders, pentameric ATPases of the AAA+ family, bind ATP to adopt an open spiral conformation that engages and opens the clamp, positions it around a primer–template junction, then hydrolyses ATP to release the closed ring onto DNA. Multiple loaders operate in parallel: the canonical RFC1–5 complex predominantly loads PCNA at replication forks, alternative complexes such as CTF18–RFC target the leading strand, and ATAD5–RFC (Elg1–RFC in yeast) specialises in unloading. The dynamic interplay of loading, sliding and unloading underpins fork stability, coordinates Okazaki fragment maturation and facilitates repair. Dysregulation of clamp loader function compromises genome integrity, with implications for ageing and cancer biology, and represents a target for therapeutic intervention.
Research from Nature Portfolio
Recent studies have elucidated the exclusive unloading mechanism of ATAD5–RFC. High‐resolution structural analysis revealed two unique locking loops and a DNA‐binding chamber plug in human ATAD5 that rigidify the complex and prevent DNA engagement, explaining its inability to load PCNA. Multiple intermediate conformers of clamp–loader complexes showed novel protomer‐specific gaps during unloading, distinct from those in loading reactions. Complementary single‐molecule investigations delineated the stepwise unloading pathway: ATAD5–RFC engages ubiquitinated and unmodified PCNA through a single intermediate state prior to ATP hydrolysis, whereas RFC traverses two sequential intermediates when loading. These insights clarify how distinct AAA+ motors achieve opposite clamp‐cycling functions and how replication factors modulate unloading activity.
Clamp Loader Dynamics in DNA Replication publication trend
The graph below shows the total number of articles in clamp loader dynamics in dna replication across all publications each year (not limited to Nature Index journals).
Technical terms
Proliferating cell nuclear antigen (PCNA): A ring‐shaped sliding clamp that encircles DNA to enhance the processivity of DNA polymerases.
Clamp loader: A pentameric AAA+ ATPase complex that opens and places the sliding clamp onto DNA in an ATP‐dependent manner.
Replication factor C (RFC): The primary eukaryotic clamp loader composed of five subunits (RFC1–5) responsible for PCNA loading at replication forks.
AAA+ ATPase domain: A conserved structural fold that binds and hydrolyses ATP to drive conformational changes in molecular machines.
3′‐ss/dsDNA junction: The primer–template boundary of a replication fork where clamp loaders position the sliding clamp.
References
- The human ATAD5 has evolved unique structural elements to function exclusively as a PCNA unloader. Nature Structural & Molecular Biology (2024).
- Cryo-EM reveals a nearly complete PCNA loading process and unique features of the human alternative clamp loader CTF18-RFC. Proceedings of the National Academy of Sciences of the United States of America (2024).
- The AAA+ superfamily: a review of the structural and mechanistic principles of these molecular machines. Critical Reviews in Biochemistry and Molecular Biology (2021).
- Control of Genome Integrity by RFC Complexes; Conductors of PCNA Loading onto and Unloading from Chromatin during DNA Replication. Genes (2017).
- Clamp loader ATPases and the evolution of DNA replication machinery. BMC Biology (2012).
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