Affinage

FBH1

F-box DNA helicase 1 · UniProt Q8NFZ0

Length
1043 aa
Mass
117.7 kDa
Annotated
2026-04-28
29 papers in source corpus 21 papers cited in narrative 21 extracted findings

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

FBH1 is a UvrD-family DNA helicase and SCF E3 ubiquitin ligase subunit that restricts homologous recombination at stalled replication forks through dual mechanisms: ATP-dependent disruption of RAD51 nucleoprotein filaments via ssDNA translocase activity, and SCF(FBH1)-mediated ubiquitylation of RAD51, both of which limit unscheduled recombination and sister chromatid exchange (PMID:24108124, PMID:25585578, PMID:16135800). FBH1 catalyzes replication fork reversal by preferentially engaging the lagging strand template, and its helicase activity cooperates with MUS81 endonuclease to generate double-strand breaks that activate ATM/DNA-PK checkpoint signaling during prolonged replication stress (PMID:25772361, PMID:23361013, PMID:23319600). Recruitment to replication factories requires PCNA interaction through a PIP degron, after which CRL4(Cdt2)-dependent proteolysis of FBH1 permits translesion synthesis polymerase access (PMID:23677613, PMID:36990095). RNF20 counteracts FBH1-mediated RAD51 filament disruption, providing an additional regulatory layer that fine-tunes recombination at damaged forks (PMID:37230987).

Mechanistic history

Synthesis pass · year-by-year structured walk · 9 steps
  1. 2005 High

    Establishing that Fbh1 controls Rad51-dependent recombination at DNA damage sites through both its F-box and helicase domains resolved a longstanding question about how recombination is negatively regulated at nucleoprotein filament assembly sites in fission yeast.

    Evidence Genetic epistasis, co-localization, and domain-specific mutant analysis in S. pombe

    PMID:16135800

    Open questions at the time
    • Mechanism of Rad51 filament disruption not biochemically defined
    • Whether FBH1 ubiquitylates recombination substrates unknown
  2. 2007 High

    Demonstrating that human FBH1 functionally substitutes for yeast Srs2 anti-recombinase and that it undergoes F-box-dependent auto-degradation established FBH1 as the vertebrate equivalent of Srs2, coupling anti-recombination activity to SCF ubiquitin ligase function.

    Evidence Cross-species complementation of S. cerevisiae srs2Δ, F-box mutant analysis, protein stability assays

    PMID:17283053 PMID:17724085

    Open questions at the time
    • Direct biochemical anti-recombinase activity not yet shown
    • Ubiquitin ligase substrates unidentified
  3. 2009 High

    Showing that FBH1 accumulates at ssDNA-containing damage sites in human cells and that its helicase/translocase activity opposes Rad51 loading defined the mechanism as ssDNA-dependent Rad51 displacement, while the discovery of SCF(Fbh1)-mediated Atf1 degradation in fission yeast revealed a separable F-box-dependent transcriptional regulatory function.

    Evidence siRNA depletion, overexpression, ssDNA quantification, SCE assays in human cells; Co-IP, phospho-mutant analysis in S. pombe

    PMID:19546232 PMID:19736316 PMID:19836238

    Open questions at the time
    • In vitro reconstitution of Rad51 filament disruption not yet performed
    • Relationship between FBH1 translocase and fork remodeling unknown
  4. 2013 High

    Biochemical reconstitution and single-molecule visualization directly demonstrated that FBH1 disrupts RAD51 filaments through ssDNA translocation, while cell-based studies revealed that FBH1 helicase activity promotes DSBs through cooperation with MUS81 and activates ATM/DNA-PK signaling during replication stress — establishing FBH1 as both an anti-recombinase and a replication stress response effector.

    Evidence In vitro reconstitution with purified proteins, single-molecule TIRF, siRNA epistasis with MUS81, DSB quantification, checkpoint kinase assays in human cells

    PMID:23319600 PMID:23361013 PMID:23393192 PMID:24108124

    Open questions at the time
    • How FBH1 remodels fork structures not resolved
    • Structural basis for FBH1-fork interaction unknown
  5. 2013 High

    Identifying PCNA as the recruitment factor for FBH1 at replication sites and showing that CRL4(Cdt2)-mediated degradation of FBH1 via a PIP degron is required for TLS polymerase access established a regulated handoff mechanism between anti-recombination and translesion synthesis.

    Evidence PCNA interaction mutants, chromatin fractionation, siRNA knockdown, TLS polymerase eta recruitment assays in human cells

    PMID:23677613

    Open questions at the time
    • Temporal regulation of FBH1 degradation during S phase not mapped
    • Whether other PIP degron proteins compete for the same pathway unknown
  6. 2014 High

    Reconstitution of SCF(Fbh1) E3 ligase activity toward Rad51 in vitro, together with demonstration that Fbh1 disrupts Rad51 filaments in an ATP-dependent manner counteracted by Swi5-Sfr1, established that FBH1 restricts recombination through two separable catalytic activities — translocase-mediated filament disruption and ubiquitin-mediated Rad51 degradation.

    Evidence Purified Fbh1-Skp1 and SCF(Fbh1) complexes, DNA strand exchange and ubiquitylation assays in vitro, genetic analysis in S. pombe

    PMID:25165823

    Open questions at the time
    • Ubiquitylation sites on Rad51 not mapped
    • In vivo contribution of ubiquitylation vs. translocase activity not separated
  7. 2015 High

    Demonstrating that FBH1 catalyzes replication fork regression in vitro and in vivo, and that SCF(FBH1)-mediated RAD51 ubiquitylation restricts RAD51 chromatin association, defined fork reversal as the structural basis for FBH1's checkpoint-activating and DSB-promoting functions.

    Evidence In vitro fork regression assay, EM of replication intermediates, ubiquitylation-resistant RAD51 mutants, recombination and fractionation assays

    PMID:25585578 PMID:25772361

    Open questions at the time
    • Which fork reversal intermediate is the MUS81 substrate unclear
    • Separation of fork regression from Rad51 displacement in vivo not achieved
  8. 2018 High

    Placing FBH1 downstream of PARP1/2 in replication fork stabilization during base excision repair demonstrated that FBH1-dependent Rad51 regulation extends beyond recombination suppression to fork protection at BER intermediates.

    Evidence PARP1/2 and Fbh1 siRNA epistasis, Rad51 focus formation, DNA fiber assay

    PMID:29467415

    Open questions at the time
    • Direct physical interaction between PARP1/2 and FBH1 not shown
    • Mechanism by which PARylation regulates FBH1 activity unknown
  9. 2023 High

    Structural determination of the PCNA–FBH1 PIP complex and identification of RNF20 as a counteractor of FBH1 Rad51 filament disruption provided the first atomic-resolution view of FBH1 recruitment and revealed a previously unknown regulatory axis balancing filament assembly and disassembly.

    Evidence X-ray crystallography and NMR of PCNA–FBH1PIP; Co-IP, in vitro strand exchange, and epistasis for RNF20–FBH1

    PMID:36990095 PMID:37230987

    Open questions at the time
    • Full-length FBH1–PCNA complex structure not available
    • How RNF20 physically shields Rad51 from FBH1 mechanistically undefined

Open questions

Synthesis pass · forward-looking unresolved questions
  • The full structural mechanism by which SCF(FBH1) engages stalled replication forks and coordinates fork reversal with RAD51 ubiquitylation remains to be established at atomic resolution from peer-reviewed studies, and the in vivo separation of FBH1's fork reversal, RAD51 displacement, and RAD51 ubiquitylation functions has not been achieved.
  • Peer-reviewed cryo-EM structure of SCF(FBH1) on fork DNA not yet published
  • In vivo separation-of-function for fork reversal vs. Rad51 ubiquitylation not accomplished
  • Physiological consequences of FBH1 loss in mammalian organismal development largely unexplored

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0003677 DNA binding 3 GO:0140657 ATP-dependent activity 3 GO:0016874 ligase activity 2 GO:0140096 catalytic activity, acting on a protein 2
Localization
GO:0005634 nucleus 3 GO:0005694 chromosome 3
Pathway
R-HSA-73894 DNA Repair 4 R-HSA-69306 DNA Replication 3 R-HSA-5357801 Programmed Cell Death 2 R-HSA-1640170 Cell Cycle 1
Partners
CDT2MUS81PCNARAD51RNF20RPASKP1
Complex memberships
SCF(FBH1)

Evidence

Reading pass · 21 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
2005 Fission yeast Fbh1 controls Rhp51 (Rad51)-dependent recombination through an interplay with mediator proteins (Rad22/Rad52, Rhp55, Swi5); both the F-box and helicase activities contribute to this control, and Fbh1 colocalizes with Rhp51 at damage-induced foci, suggesting the interplay occurs at nucleoprotein filament assembly sites. Genetic epistasis (deletion suppressor analysis), indirect immunofluorescence co-localization, allele-specific mutant analysis in S. pombe Molecular and cellular biology High 16135800
2007 Human FBH1 functionally substitutes for S. cerevisiae Srs2 in suppressing unscheduled recombination; the F-box domain is required for this function and for DNA damage-induced auto-degradation of hFBH1 via SCF ubiquitin ligase activity. Complementation assay in S. cerevisiae srs2 mutants, F-box domain mutant analysis, protein stability assay Molecular and cellular biology High 17724085
2007 Vertebrate Fbh1 acts in parallel with BLM helicase to prevent crossover recombination at replication blocks; FBH1-deficient DT40 cells show increased sister chromatid exchange and radial chromosome formation without a general HR defect. Gene disruption in DT40 cells, SCE assay, double-mutant analysis (FBH1/BLM, FBH1/RAD54) Molecular and cellular biology High 17283053
2008 In S. pombe, the F-box domain of Fbh1 is required for nuclear localization and damage-induced focus formation, while the helicase domain mutation causes constitutive focus accumulation; SCF(Fbh1) complex assembly is prerequisite for recombination function. GFP fusion localization, NLS-rescue experiments, domain-specific point mutants in S. pombe BMC molecular biology Medium 18312697
2009 Human Fbh1 accumulates at DNA damage/replication stress sites dependent on its helicase activity and partially on its F-box; it interacts with ssDNA and its recruitment requires ssDNA formation; elevated Fbh1 impairs Rad51 recruitment while its depletion increases chromatin-associated Rad51 and unscheduled SCE. siRNA depletion, ectopic overexpression, immunofluorescence, ssDNA quantification, SCE assay in human cells The Journal of cell biology High 19736316
2009 S. pombe Fbh1 limits Rad51 loading onto DNA at blocked replication forks in direct opposition to Rad22 (Rad52 orthologue); this activity depends on DNA helicase/translocase activity, consistent with Fbh1 acting as a Rad51 disruptase; Fbh1 overexpression reduces replication fork block-induced recombination and Rad51 foci. Genetic assays, indirect immunofluorescence, overexpression/suppressor analysis, allele-specific helicase mutants in S. pombe Molecular and cellular biology High 19546232
2009 S. pombe Fbh1 targets the transcription factor Atf1 for SCF-mediated ubiquitin-proteasome degradation under basal conditions; stress-induced MAPK phosphorylation of Atf1 abrogates its interaction with the Fbh1 F-box, stabilizing Atf1; this function requires an intact F-box but not helicase activity. Co-immunoprecipitation, protein stability/degradation assays, phosphorylation-site mutant analysis in S. pombe Current biology High 19836238
2010 Mouse Fbh1 is required for normal mitotic progression following decatenation stress; Fbh1-deficient cells are hypersensitive to topoisomerase II catalytic inhibitors and display defects in anaphase chromosome separation; F-box deletion reduces Rad51 localization to damage and increases cytoplasmic Rad51. Homozygous knockout and F-box deletion mouse ES cell lines, topoisomerase II inhibitor sensitivity, chromosome segregation assay, Rad51 localization by immunofluorescence DNA repair Medium 20457012
2013 Human FBH1 physically interacts with RPA and promotes DNA double-strand break formation following replication stress in a helicase-dependent manner; FBH1 depletion reduces DSBs, ATM/DNA-PK activation, RPA2 and p53 phosphorylation, and increases cell survival after replication stress. Affinity purification/MS (identification of RPA interaction), siRNA depletion, helicase-dead mutant rescue, DSB quantification, kinase activation assays in human cells The Journal of cell biology High 23319600
2013 Human FBH1 binds directly to RAD51 and disrupts RAD51 nucleoprotein filaments on DNA through its ssDNA translocase function; FBH1 helicase domain deletion in mouse ES cells leads to elevated RAD51 chromatin association and hyper-recombination. In vitro biochemical reconstitution, single-molecule TIRF microscopy, direct binding assays, helicase deletion mouse ES cell line, recombination assays The Journal of biological chemistry High 24108124
2013 FBH1 cooperates with MUS81 nuclease to promote endonucleolytic DNA cleavage and double-strand break formation following prolonged replication stress; FBH1 helicase activity is required for this cooperation; FBH1-deficient cells show reduced DSBs and resistance to hydroxyurea-induced killing. siRNA depletion of FBH1 and MUS81/EME1, DSB quantification (γH2AX, comet assay), cell viability assays, helicase-dead mutant analysis Nature communications High 23361013
2013 PCNA is critical for FBH1 recruitment to replication factories and DNA damage sites; FBH1 is subsequently degraded by the CRL4(Cdt2)-PCNA pathway via a PIP degron; expression of non-degradable FBH1 impairs TLS polymerase eta recruitment to chromatin after UV damage. PCNA interaction mutants, co-immunoprecipitation, protein stability assays, siRNA knockdown, chromatin fractionation, immunofluorescence in human cells Nucleic acids research High 23677613
2013 Ubiquitylation of FBH1 affects its interaction with the RAD51 nucleoprotein filament but not its translocase and helicase activities, as revealed by single-molecule sorting of ubiquitylated vs. non-ubiquitylated FBH1 molecules from human cells. Single-molecule TIRF microscopy (single-molecule sorting), native FBH1 isolated from human cells Nucleic acids research Medium 23393192
2014 Purified fission yeast Fbh1-Skp1 complex disrupts Rad51 nucleoprotein filaments in an ATP-dependent manner and inhibits Rad51-driven DNA strand exchange; the Swi5-Sfr1 complex alleviates this disruption. The reconstituted SCF(Fbh1) complex displays E3 ubiquitin ligase activity toward Rad51, and Fbh1 reduces Rad51 protein levels in stationary phase in an F-box-dependent manner. In vitro reconstitution of purified Fbh1-Skp1 and SCFFbh1 complexes, DNA strand exchange assay, ubiquitylation assay, genetic analysis in S. pombe PLoS genetics High 25165823
2015 FBH1 catalyzes regression of a model replication fork in vitro and promotes fork regression in vivo in response to replication perturbation; through its helicase activity, FBH1 is required for early ATM substrate phosphorylation (CHK2, CtIP) and RPA hyperphosphorylation prior to DSB formation, promoting checkpoint signaling. In vitro fork regression assay, electron microscopy of replication intermediates in vivo, phosphorylation assays, helicase-dead mutant analysis Cell reports High 25772361
2015 The SCF(FBH1) complex ubiquitylates RAD51; expression of ubiquitylation-resistant RAD51 in human cells causes hyperrecombination and enhanced nuclear matrix association, indicating FBH1-mediated RAD51 ubiquitylation restricts RAD51 function. In vitro ubiquitylation assay with SCF(FBH1), ubiquitylation-resistant RAD51 mutant expression, recombination assays, nuclear matrix fractionation Nature communications High 25585578
2018 PARP2 stabilizes replication forks encountering BER intermediates through Fbh1-dependent regulation of Rad51; combined loss of PARP1 and PARP2 leads to elevated replication-associated DNA damage due to inability to stabilize Rad51 at damaged forks and prevention of uncontrolled DNA resection, placing Fbh1 downstream of PARP1/2 in BER-associated fork stability. PARP1/2 siRNA depletion, Fbh1 siRNA depletion, epistasis analysis, Rad51 focus formation assay, DNA fiber assay Nature communications High 29467415
2023 The crystal structure of PCNA in complex with FBH1PIP and NMR perturbation analysis reveal that FBH1 contains two PCNA-binding motifs (PIP and APIM) with overlapping binding sites on PCNA, with FBH1PIP providing the dominant contribution to the interaction. X-ray crystallography (PCNA-FBH1PIP co-crystal), NMR chemical shift perturbation analysis Structure High 36990095
2023 Yeast Bre1 and its human homolog RNF20 interact with FBH1 helicase to counteract its disrupting effect on the Rad51 filament, providing an additional layer of Rad51 filament protection; RNF20 also promotes Rad51 filament formation in vitro independently of its ligase activity. Co-immunoprecipitation, in vitro DNA strand exchange assay, Rad51 filament assembly assay, epistasis in yeast and human cells Nature communications High 37230987
2025 Cryo-EM structure of SCF(FBH1) bound to a stalled fork DNA reveals preferential binding to the lagging strand template, which stimulates helicase activity and is required for fork reversal; disruption of the fork junction interface severely curtails fork reversal in vitro and replication progression in cells; the structure also provides a model for RAD51 filament disassembly through translocation and ubiquitination at the lagging strand. Cryo-EM structure determination, in vitro fork reversal assay, interface mutant analysis, DNA replication progression assay in cells bioRxivpreprint High bio_10.1101_2025.09.30.679681
2025 FBH1 limits replication fork progression by PRIMPOL in response to hydroxyurea; however, PRIMPOL-mediated synthesis is distinct from the mechanism by which FBH1 promotes DSB accumulation, indicating these are separable functions. FBH1 knockout cells, PRIMPOL depletion, DNA fiber assay, DSB quantification bioRxivpreprint Medium 40672194

Source papers

Stage 0 corpus · 29 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2018 PARP1 and PARP2 stabilise replication forks at base excision repair intermediates through Fbh1-dependent Rad51 regulation. Nature communications 191 29467415
2005 The F-Box DNA helicase Fbh1 prevents Rhp51-dependent recombination without mediator proteins. Molecular and cellular biology 108 16135800
2015 FBH1 Catalyzes Regression of Stalled Replication Forks. Cell reports 95 25772361
2009 Human Fbh1 helicase contributes to genome maintenance via pro- and anti-recombinase activities. The Journal of cell biology 90 19736316
2013 FBH1 helicase disrupts RAD51 filaments in vitro and modulates homologous recombination in mammalian cells. The Journal of biological chemistry 81 24108124
2013 FBH1 co-operates with MUS81 in inducing DNA double-strand breaks and cell death following replication stress. Nature communications 80 23361013
2013 The helicase FBH1 is tightly regulated by PCNA via CRL4(Cdt2)-mediated proteolysis in human cells. Nucleic acids research 69 23677613
2009 Fbh1 limits Rad51-dependent recombination at blocked replication forks. Molecular and cellular biology 68 19546232
2015 FBH1 influences DNA replication fork stability and homologous recombination through ubiquitylation of RAD51. Nature communications 58 25585578
2007 The human F-Box DNA helicase FBH1 faces Saccharomyces cerevisiae Srs2 and postreplication repair pathway roles. Molecular and cellular biology 53 17724085
2013 FBH1 promotes DNA double-strand breakage and apoptosis in response to DNA replication stress. The Journal of cell biology 47 23319600
2007 Cooperative roles of vertebrate Fbh1 and Blm DNA helicases in avoidance of crossovers during recombination initiated by replication fork collapse. Molecular and cellular biology 41 17283053
2014 FBH1 affects warm temperature responses in the Arabidopsis circadian clock. Proceedings of the National Academy of Sciences of the United States of America 36 25246594
2014 Multiple regulation of Rad51-mediated homologous recombination by fission yeast Fbh1. PLoS genetics 34 25165823
2013 Single-molecule sorting reveals how ubiquitylation affects substrate recognition and activities of FBH1 helicase. Nucleic acids research 31 23393192
2013 FBH1 protects melanocytes from transformation and is deregulated in melanomas. Cell cycle (Georgetown, Tex.) 22 23466708
2009 Stress-induced phosphorylation of S. pombe Atf1 abrogates its interaction with F box protein Fbh1. Current biology : CB 21 19836238
2010 Mammalian Fbh1 is important to restore normal mitotic progression following decatenation stress. DNA repair 20 20457012
2008 Essential and distinct roles of the F-box and helicase domains of Fbh1 in DNA damage repair. BMC molecular biology 19 18312697
2023 Bre1/RNF20 promotes Rad51-mediated strand exchange and antagonizes the Srs2/FBH1 helicases. Nature communications 12 37230987
2023 LncRNA FBXO18-AS promotes gastric cancer progression by TGF-β1/Smad signaling. European journal of histochemistry : EJH 9 37340903
2023 Molecular insight into the PCNA-binding mode of FBH1. Structure (London, England : 1993) 6 36990095
2023 F-box DNA Helicase 1 (FBH1) Contributes to the Destabilization of DNA Damage Repair Machinery in Human Cancers. Cancers 5 37760409
2023 FBH1 deficiency sensitizes cells to WEE1 inhibition by promoting mitotic catastrophe. DNA repair 5 38103522
2004 Structure of gene coding for the fruit body-specific hydrophobin Fbh1 of the edible basidiomycete Pleurotus ostreatus. Mycologia 4 21148831
2025 FBH1 and the replication stress response: Implications for genome stability and cancer development. DNA repair 3 40582249
2025 PRIMPOL promotes replication fork progression but not double strand break formation in FBH1-deficient cells in response to hydroxyurea. bioRxiv : the preprint server for biology 2 40672194
2017 Rare FBXO18 variations and risk of schizophrenia: Whole-exome sequencing in two parent-affected offspring trios followed by resequencing and case-control studies. Psychiatry and clinical neurosciences 2 28317220
2023 FBH1 deficiency sensitizes cells to WEE1 inhibition by promoting mitotic catastrophe. bioRxiv : the preprint server for biology 0 37292855