What the study found
The human CTF18-RFC clamp loader has a distinctive structure when bound to PCNA, the proliferating cell nuclear antigen that helps DNA polymerases work processively. The study found that its RFC module adopts an autoinhibited conformation similar to canonical RFC, and that its regulatory subunits are flexibly attached.
Why the authors say this matters
The authors conclude that these structural features provide insight into PCNA loading and into the stimulation of leading strand synthesis by Pol epsilon, the leading strand DNA polymerase. The findings indicate that CTF18-RFC has unique elements that relate to its role in DNA replication.
What the researchers tested
The researchers used cryo-electron microscopy to characterize the human CTF18-RFC complex and its interaction with PCNA. They examined the positions of the Ctf8 and Dcc1 regulatory subunits, the RFC module, and the RFC1 large subunit, and they tested the effect of deleting a beta-hairpin in RFC1.
What worked and what didn't
The cryo-EM data supported that Ctf8 and Dcc1 are flexibly tethered to the RFC module. A 2.9 angstrom structure showed the RFC module bound to PCNA in an autoinhibited conformation, and the RFC1 subunit was anchored to PCNA through an atypical low-affinity PIP box and to RFC5 through a novel beta-hairpin. Removing the beta-hairpin impaired CTF18-RFC-PCNA complex stability, slowed clamp loading, and decreased the rate of primer synthesis by Pol epsilon.
What to keep in mind
The summary provided does not describe broader limitations beyond the specific structural and functional observations reported here. The findings are based on cryo-EM structural analysis and the beta-hairpin deletion test in this complex.
Key points
- CTF18-RFC binds PCNA in an autoinhibited conformation similar to canonical RFC.
- The Ctf8 and Dcc1 regulatory subunits are flexibly tethered to the RFC module.
- RFC1 uses an atypical low-affinity PIP box and a novel beta-hairpin to engage PCNA and RFC5.
- Deleting the beta-hairpin weakens complex stability, slows clamp loading, and reduces Pol epsilon primer synthesis.
- The authors say the structure provides insight into PCNA loading and leading strand synthesis.
Disclosure
- Research title:
- CTF18-RFC binds PCNA in an autoinhibited loading state
- Authors:
- Giuseppina R. Briola, Mohammad Tehseen, Amani Al-Amodi, Grace Young, Ammar Usman Danazumi, Phong Quoc Nguyen, Christos G. Savva, Mark Hedglin, Samir M. Hamdan, Alfredo De Biasio
- Institutions:
- King Abdullah University of Science and Technology, King Abdullah University of Science and Technology, King Abdullah University of Science and Technology, King Abdullah University of Science and Technology, King Abdullah University of Science and Technology, King Abdullah University of Science and Technology, King Abdullah University of Science and Technology, King Abdullah University of Science and Technology, Pennsylvania State University, Pennsylvania State University
- Publication date:
- 2026-02-23
- OpenAlex record:
- View
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