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| Title | The E. coli DnaX clamp loader sharply bends DNA to load β-clamp at nicks and small gaps. |
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| Journal, issue, pages | Mol Cell, Vol. 86, Issue 11, Page 2055-2069.e10, Year 2026 |
| Publish date | Jun 4, 2026 |
Authors | Fengwei Zheng / Nina Y Yao / Roxana E Georgescu / Meinan Lyu / Michael E O'Donnell / Huilin Li / ![]() |
| PubMed Abstract | DNA sliding clamps are essential for processive DNA synthesis in all domains of life and are loaded by ATP-dependent clamp loaders that recognize recessed 3' ends. How clamp loaders function at nicks ...DNA sliding clamps are essential for processive DNA synthesis in all domains of life and are loaded by ATP-dependent clamp loaders that recognize recessed 3' ends. How clamp loaders function at nicks and small single-stranded DNA (ssDNA) gaps-common DNA repair intermediates-remains unclear. Here, we show that the bacterial E. coli DnaX clamp loader uses a mechanism distinct from its eukaryotic counterpart. Whereas eukaryotic replication factor C (RFC) unwinds DNA at the recessed 3' end and stabilizes the 5'-dsDNA (double-stranded DNA) at a shoulder site, the bacterial DnaX-complex neither unwinds DNA nor stably binds the 5'-dsDNA in vitro. Instead, cryo-EM structures reveal that the β-clamp contains a conserved external DNA-binding site that bends gapped DNA by ∼150°, promoting insertion of 3'-dsDNA into the clamp. This DNA-bending mechanism enables efficient β-clamp loading at nicks and small gaps and reveals a distinct bacterial strategy likely important for DNA repair. |
External links | Mol Cell / PubMed:42140189 / PubMed Central |
| Methods | EM (single particle) |
| Resolution | 2.53 - 5.5 Å |
| Structure data | EMDB-71013: Cryo-EM map of the E. coli clamp loader DnaX-complex loading beta-clamp onto 1-nt gapped DNA in state 1 conformer 1 with flexibly bound DNA at the shoulder EMDB-71014: Cryo-EM map of the E. coli clamp loader DnaX-complex loading beta-clamp onto 1-nt gapped DNA in state 1 conformer 2 with flexibly bound DNA at the shoulder EMDB-71015: Cryo-EM map of the E. coli clamp loader DnaX-complex loading beta-clamp onto 1-nt gapped DNA in state 1 conformer 3 with disordered DNA at the shoulder EMDB-71016: Cryo-EM map of the E. coli clamp loader DnaX-complex loading beta-clamp onto 1-nt gapped DNA in state 2 conformer 1 with sharply bent DNA EMDB-71017: Cryo-EM map of the E. coli clamp loader DnaX-complex loading beta-clamp onto 1-nt gapped DNA in state 2 conformer 2 with less bent DNA EMDB-71018: Cryo-EM map of the E. coli clamp loader DnaX-complex alone ![]() EMDB-71019: Consensus map of E. coli clamp loader DnaX-complex loading beta-clamp onto 10-nt gapped DNA in state 1 the DNA recognition state ![]() EMDB-71020: Focus refined map of E. coli clamp loader sub-complex Psi-Chi EMDB-71021: Cryo-EM map of the E. coli clamp loader DnaX-complex loading beta-clamp onto 10-nt gapped DNA in state 1 the DNA recognition state EMDB-71022: Cryo-EM map of the E. coli clamp loader DnaX-complex loading beta-clamp onto 10-nt gapped DNA in state 2 conformer 1 with fully open clamp and unsettled DNA EMDB-71023: Cryo-EM map of the E. coli clamp loader DnaX-complex loading beta-clamp onto 10-nt gapped DNA in state 2 conformer 2 with fully open clamp and settled DNA EMDB-71024: Cryo-EM map of the E. coli clamp loader DnaX-complex loading beta-clamp onto 10-nt gapped DNA in state 2 conformer 3 with partially closed clamp EMDB-71025: Cryo-EM map of the E. coli clamp loader DnaX-complex loading beta-clamp onto 10-nt gapped DNA in state 2 conformer 4 with fully closed clamp EMDB-71026: Cryo-EM map of the E. coli clamp loader DnaX-complex loading beta-clamp onto 10-nt gapped DNA in state 2 conformer 5 with fully closed clamp EMDB-71027: Cryo-EM map of the E. coli clamp loader DnaX-complex loading beta-clamp onto 10-nt gapped DNA in state 2 conformer 6 with fully closed clamp |
| Chemicals | ![]() ChemComp-ZN: ![]() ChemComp-AGS: ![]() ChemComp-MG: ![]() ChemComp-ADP: |
| Source |
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Keywords | REPLICATION/DNA / E. coli / DNA replication / DNA damage repair / clamp loading complex / clamp beta / clamp loader DnaX-complex / REPLICATION / REPLICATION-DNA complex / TRANSFERASE |
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