Deep Research
Bioreason Pro
(fen1-deep-research-bioreason-sft.md)
Bioreason Pro
(fen1-deep-research-bioreason-sft.md)Thinking Trace
I begin with the InterPro architecture. The polypeptide is dominated by XPG/Rad2 nuclease signatures: IPR006084 (XPG/Rad2 endonuclease family, residues 1โ357) and the more specific IPR023426 (Flap endonuclease 1 family, residues 1โ345) define the enzyme class and substrate preference. The N-terminus contains IPR006085 (XPG, N-terminal domain, residues 1โ107), which houses catalytic and metal-binding residues for the nuclease core. Multiple overlapping XPG/Rad2 family motifs punctuate this region and the adjacent IPR006086 (XPG-I domain, residues 146โ218; also detected as residues 149โ233), forming the paired N and I subdomains that clamp DNA and position the scissile phosphate. These include IPR019974 (XPG conserved site, residues 79โ93) and additional conserved motifs at residues 149โ163 and 166โ186, which together create the acidic residues that coordinate divalent metal ions and the helix-hairpin-helix elements that stabilize the DNA backbone. The catalytic core is further supported by IPR029060 (PIN-like domain superfamily, residues 2โ233), a nuclease fold that contributes the metal-chelating geometry, and by IPR008918 (Helix-hairpin-helix motif, class 2, residues 220โ253), which provides non-sequence-specific DNA binding and bends the duplex near the junction. The C-terminal region is captured by IPR036279 (5'-3' exonuclease, C-terminal domain superfamily, residues 218โ351), a regulatory and DNA-binding module that recognizes 5'-flap architecture and stimulates catalysis. Together, these domains assemble the canonical Rad2/XPG-like nuclease that incises 5'-flaps at single-strand/double-strand junctions and also supports 5'โ3' exonucleolytic degradation on nicked or gapped duplex DNA.
This domain architecture causes a precise molecular function: GO:0017108 5'-flap endonuclease activity. The XPG-N/I composite active site, reinforced by the HhH motif, binds a 5'-flap and introduces a single endonucleolytic cut 5' to the branch, leaving a ligatable nick. The C-terminal superfamily domain enhances recognition and positioning of the flap stem, while the PIN-like fold coordinates catalytic metal ions to hydrolyze the phosphodiester bond. The same structural features enable processive 5'โ3' exonucleolysis on nicked or gapped duplexes, consistent with a distributive-to-processive switch depending on DNA context and partner binding.
From this chemistry, the biological processes follow. During lagging-strand DNA replication, displacement synthesis by DNA polymerase generates 5'-flaps on downstream Okazaki fragments; this nuclease resolves those flaps to enable ligation, placing it in DNA replication and specifically Okazaki fragment processing. In base-excision repair, long-patch BER creates 5'-flaps after gap filling; the enzyme trims these flaps to complete repair, aligning with base-excision repair and long-patch BER. Its ability to incise at ssDNAโdsDNA junctions and to degrade 5'-protrusions also supports DNA recombination and the processing of recombination intermediates. The same incision and resection activities contribute to double-strand break repair, including homologous recombination and nonhomologous end joining interfaces that require flap and overhang management. In metazoan tissues, such genome-maintenance activities are essential for proliferative and differentiating cells; thus, defects manifest in organogenesis, including retina development in the camera-type eye, where precise DNA repair and replication are required for photoreceptor and retinal pigment epithelium maturation.
The cellular component is dictated by the need to access chromosomal DNA and replication factories. The presence of nuclear-targeted DNA repair and replication roles, together with the regulatory C-terminal domain that engages replication clamps, places the enzyme in the GO:0005634 nucleus. The architecture lacks transmembrane segments or secretion signals, reinforcing a soluble nuclear localization.
Mechanistically, the enzyme likely operates within multi-protein assemblies. The C-terminal domain and HhH-mediated DNA engagement allow it to be clamped by the sliding clamp PCNA, which increases processivity and coordinates handoff to DNA ligase. DNA polymerase delta and its regulatory subunits generate the 5'-flaps that this nuclease removes; DNA polymerase beta participates in long-patch BER where the same flap-removal step is required. Helicase/nuclease Dna2 and the RecQ helicase WRN create or extend DNA flaps and suppress toxic recombination intermediates; the nuclease can then trim or process these structures. AP endonuclease (DNA-(apurinic or apyrimidinic site) lyase) generates entry points for repair synthesis that culminate in flap formation, which this enzyme resolves. In double-strand break contexts, coordination with XRCC1-like scaffolds and double-strand break repair proteins organizes repair tracts where flap processing is needed. Altogether, the domain architecture and partner repertoire support a model in which the enzyme is a nuclear 5'-flap endonuclease and 5'โ3' exonuclease that acts at replication forks, BER patches, and recombination/DSB sites to maintain genome integrity and enable proper tissue development, including the retina.
## Functional Summary
A nuclear nuclease that removes 5โฒ flaps and degrades 5โฒ ends to resolve replication and repair intermediates. During lagging-strand synthesis it cleaves displaced DNA on Okazaki fragments, and in long-patch base-excision repair it trims flap structures created after gap filling. Its incision at single- to double-strand junctions and exonucleolytic processing of nicked or gapped duplexes support recombination and double-strand break repair. By coordinating with sliding clamps, polymerases, helicases, and ligases, it ensures accurate maturation of DNA ends, a role that underpins genome stability and contributes to proper development of tissues such as the retina.
## UniProt Summary
Key enzyme involved in DNA replication and repair. Has 5'-flap endonuclease activity during DNA replication of the lagging strand: tracks along the 5'-end of a flap structure emerging from the displacement synthesis of the downstream Okazaki fragment and cleaves the flap structure at the junction with the leading strand (By similarity). Has a 5'--> 3'-exonuclease activity on nicked or gapped double-stranded DNA (By similarity). Also involved in the repair of DNA double-strand breaks by non-homologous end joining (NHEJ) and homologous recombination (By similarity). Has endonuclease activity towards double-stranded DNA with a single-strand gap, introducing a cut near the junction between the single- and double-stranded sections (By similarity). Has exonuclease activity on nicked or gapped double-stranded DNA (By similarity).
## InterPro Domains
- IPR006084: XPG/Rad2 endonuclease (family) [1-357]
- IPR006085: XPG, N-terminal (domain) [1-107]
- IPR023426: Flap endonuclease 1 (family) [1-345]
- IPR029060: PIN-like domain superfamily (homologous_superfamily) [2-233]
- IPR006084: XPG/Rad2 endonuclease (family) [28-42]
- IPR019974: XPG conserved site (conserved_site) [79-93]
- IPR006084: XPG/Rad2 endonuclease (family) [81-100]
- IPR006084: XPG/Rad2 endonuclease (family) [145-162]
- IPR006086: XPG-I domain (domain) [146-218]
- IPR006086: XPG-I domain (domain) [149-233]
- IPR019974: XPG conserved site (conserved_site) [149-163]
- IPR006084: XPG/Rad2 endonuclease (family) [166-186]
- IPR036279: 5'-3' exonuclease, C-terminal domain superfamily (homologous_superfamily) [218-351]
- IPR008918: Helix-hairpin-helix motif, class 2 (conserved_site) [220-253]
- IPR006084: XPG/Rad2 endonuclease (family) [223-238]
## GO Term Predictions
### Molecular Function
### Biological Process
### Cellular Component
Falcon
(fen1-deep-research-falcon.md)
Falcon
(fen1-deep-research-falcon.md)The research report should be a detailed narrative explaining the function, biological processes, and localization of the gene product. Citations should be given for all claims.
You should prioritize authoritative reviews and primary scientific literature when conducting research. You can supplement
this with annotations you find in gene/protein databases, but these can be outdated or inaccurate.
We are specifically interested in the primary function of the gene - for enzymes, what reaction is catalyzed, and what is the substrate specificity? For transporters, what is the substrate? For structural proteins or adapters, what is the broader structural role? For signaling molecules, what is the role in the pathway.
We are interested in where in or outside the cell the gene product carries out its function.
We are also interested in the signaling or biochemical pathways in which the gene functions. We are less interested in broad pleiotropic effects, except where these elucidate the precise role.
Include evidence where possible. We are interested in both experimental evidence as well as inference from structure, evolution, or bioinformatic analysis. Precise studies should be prioritized over high-throughput, where available.
Research report: Danio rerio fen1 (UniProt Q6TNU4) โ functional annotation and current evidence
1) Target verification (gene/protein identity)
The UniProt target Q6TNU4 is annotated as Flap endonuclease 1 (FEN1; flap structure-specific endonuclease 1) from Danio rerio, belonging to the conserved XPG/RAD2 nuclease family; the retrieved literature consistently uses FEN1/FEN-1 to denote the canonical structure-specific 5โฒ-flap endonuclease central to DNA replication and repair pathways, and zebrafish-specific studies assay fen1 transcript using zebrafish primers, aligning with this identity (lu2021theoxidativestress pages 2-3).
2) Key concepts and definitions (current understanding)
2.1 Structure-specific nuclease and โflapโ substrates
FEN1 is a structure-specific nuclease that recognizes DNA flap and nicked structures (not a specific sequence) and hydrolyzes phosphodiester bonds using a two-metal (Mg2+) catalytic center typical for this nuclease class (sun2024structurespecificnucleasesin pages 2-3).
2.2 Canonical biochemical activities attributed to FEN1
A key mechanistic framework is that FEN1 is multifunctional, with at least three biochemically distinguishable nuclease activities described in the literature: flap endonuclease (FEN), 5โฒ exonuclease (EXO), and gap endonuclease (GEN) (xu2018sumo1modificationof pages 2-3). In cellular DNA metabolism, these activities are primarily discussed in the contexts of (i) lagging-strand replication and (ii) repair synthesis that generates short displaced 5โฒ flaps (xu2018sumo1modificationof pages 2-3, sun2023okazakifragmentmaturation pages 9-11).
2.3 Pathway context: Okazaki fragment maturation (OFM)
During lagging-strand DNA replication, strand-displacement synthesis produces short 5โฒ flaps that must be removed prior to ligation. An authoritative synthesis of the field describes FEN1 as the primary endonuclease that cleaves these short RNAโDNA/DNA flaps to enable Okazaki fragment joining; failure to process flaps blocks ligation and generates toxic intermediates that can trigger backup pathways (sun2023okazakifragmentmaturation pages 9-11).
2.4 Pathway context: long-patch base excision repair (LP-BER)
In LP-BER, repair synthesis can displace a short segment of DNA, creating a 5โฒ flap that must be cleaved; FEN1 is repeatedly described as a core LP-BER flap nuclease (krasikova2024doesthexpaโfen1 pages 1-2, xu2018sumo1modificationof pages 2-3).
3) Enzymatic function: reaction and substrate specificity
Functionally, FEN1 catalyzes hydrolytic cleavage of phosphodiester bonds in 5โฒ-flap (and related nick/gap) substrates, producing ligatable nicked DNA products in replication and repair intermediates (sun2023flapendonuclease1 pages 3-5, sun2024structurespecificnucleasesin pages 2-3). In the most current structural model for eukaryotic OFM, Okazaki primers are ~30 nt (8โ12 nt RNA + 10โ20 nt DNA), Pol ฮด generates short flaps typically ~2โ10 nt, and FEN1 removes flap/nick intermediates iteratively in coordination with RNaseH2 and PCNA to complete primer removal and ligation-ready processing (tian2024structuralinsightinto pages 1-2).
4) Cellular localization and molecular context
4.1 Nuclear/chromatin association during replication
The most direct mechanistic evidence in the retrieved corpus places FEN1 on chromatin through its interaction with the sliding clamp PCNA, and through purification of endogenous PCNAโFEN1 complexes from native chromatin for cryo-EM analysis (tian2024structuralinsightinto pages 1-2). This supports the functional interpretation that FEN1 acts primarily in the nucleus at replication/repair sites, rather than as a soluble enzyme.
4.2 Recruitment to sites of DNA damage (DPCs)
Recent DPC-repair work describes FEN1 recruitment to DNAโprotein crosslinks (DPCs) as regulated by PARP1/PARG-dependent ADP-ribosylation, consistent with localized nuclear recruitment to DNA damage sites (sun2023flapendonuclease1 pages 9-11, saha2024parp1drivenrepairof pages 1-3).
5) Pathways and interaction partners (mechanistic integration)
5.1 PCNA โtoolbeltโ coordination of OFM (major 2024 advance)
A central 2024 development is cryo-EM structural resolution of endogenous PCNAโFEN1 and PCNAโFEN1โRNaseH2 complexes, capturing multiple primer-removal states. These structures support a toolbelt mechanism in which PCNA can coordinate multiple PIP-box proteins, and show that product release from FEN1 is a rate-limiting step in the OFM reaction cycle (tian2024structuralinsightinto pages 1-2). Structurally, the complexes were reported at 3.5โ3.8 ร resolution, with FEN1 binding one PCNA protomer via its PIP box/IDCL interactions, and the DNA adopting an L-shaped path through the complex (tian2024structuralinsightinto pages 4-6). In vitro, PCNA is reported to increase FEN1 activity by approximately ~10โ50-fold (tian2024structuralinsightinto pages 1-2).
5.2 RNaseH2 interplay during primer removal
The same 2024 structural work suggests an unrecognized role for RNaseH2 as a dsDNA-binding factor that can promote FEN1 flap cleavage via PCNA-mediated conformational modulation of the DNA substrate, strengthening the model that primer removal is a coordinated multi-enzyme process rather than purely sequential hand-offs (tian2024structuralinsightinto pages 1-2).
5.3 PARP1/PARG axis and FEN1 in DNAโprotein crosslink repair (2023โ2024)
Two recent studies position FEN1 in PARP-driven DPC-repair pathways.
* A 2023 preprint reports that FEN1 can excise formaldehyde-induced DPC-associated flap-like substrates and enzymatic TOP2-DPCs, with recruitment mediated by PARylation; an E285 residue is identified as a major ADP-ribosylation site required for relocalization to DPCs, while PARylation does not measurably change intrinsic flap nuclease activity in vitro (sun2023flapendonuclease1 pages 9-11).
* A 2024 Cell Reports study reports PARP1-driven recruitment of FEN1 to TOP3A-DPCs, with pathway choice shaped by crosstalk between PARylation and ubiquitylation (saha2024parp1drivenrepairof pages 1-3).
5.4 Cross-talk with other repair pathways (NER-associated factors)
A 2024 Biomolecules study demonstrates formation of XPAโFEN1โDNA ternary complexes on defined flap/gap substrates and reports that XPA can moderately inhibit FEN1 activity in vitro, supporting models in which FEN1 may be engaged beyond classical BER/replication, potentially including NER-associated resynthesis steps (krasikova2024doesthexpaโfen1 pages 1-2).
6) Zebrafish (Danio rerio) evidence: expression regulation and experimental usage
Direct zebrafish functional genetics (loss-of-function phenotypes of fen1) were not retrieved in the current document set; therefore, the zebrafish-specific annotation here is based on (i) zebrafish transcript-level evidence in toxicology/DDR contexts and (ii) zebrafish as an in vivo platform that has used FEN1-derived engineering.
6.1 Zebrafish larval BER-pathway response: fen1 mRNA induction under oxidative stressors
A zebrafish ecotoxicology study explicitly assays fen1 among BER genes by qPCR in zebrafish larvae, providing zebrafish-specific assay details including a fen1 primer (forward sequence shown in the paper), amplicon length (138 bp), and PCR efficiency (100%) (lu2021theoxidativestress pages 2-3). Larvae were exposed from 4 hours post-fertilization (hpf) to phthalate-related compounds including DBP (0โ0.5โ5 ฮผM) and MEHP/DEHP (0โ10โ25โ50 ฮผM) across time windows spanning hours to days (lu2021theoxidativestress pages 2-3). The paperโs zebrafish qPCR figures (heatmap and bar plots) show significant fen1 upregulation in zebrafish under multiple exposure conditions (lu2021theoxidativestress media 0d94d88c, lu2021theoxidativestress media b881018e, lu2021theoxidativestress media 38921355, lu2021theoxidativestress media 1bd7b56f).
Interpretation for functional annotation: this supports that zebrafish fen1 is transcriptionally responsive in contexts interpreted by the authors as oxidative stress/DNA damage with BER pathway engagement, consistent with the canonical role of FEN1 in LP-BER and replication-associated repair (lu2021theoxidativestress pages 2-3, xu2018sumo1modificationof pages 2-3).
6.2 Zebrafish in vivo implementation: structure-guided nuclease (SGN) for genome editing
A notable real-world implementation using zebrafish embryos is a 2016 Genome Biology study that engineered a structure-guided endonuclease (SGN) composed of FEN-1 (structure recognition of a flap) fused to the FokI cleavage domain, and demonstrated cleavage of reporter and endogenous loci in zebrafish embryos after microinjection into Tg(flk1:eGFP) fish (xu2016analternativenovel pages 1-2). While this work does not establish fen1โs endogenous zebrafish developmental function, it demonstrates that flap-structure recognition by FEN1 can be operationalized as a programmable genome engineering strategy in zebrafish (xu2016analternativenovel pages 1-2).
7) Recent developments and โexpert viewโ synthesis (2023โ2024 priority)
Three convergent 2023โ2024 themes emerge from authoritative reviews and primary research:
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OFM as a coordinated, PCNA-organized multi-enzyme process (toolbelt models): High-resolution structural snapshots now directly visualize PCNA-bound assemblies of FEN1 (and RNaseH2), strengthening mechanistic models in which PCNA scaffolds OFM and modulates enzyme conformations and DNA geometry (tian2024structuralinsightinto pages 1-2, tian2024structuralinsightinto pages 4-6).
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FEN1 beyond canonical OFM/BER: processing DNAโprotein crosslinks under PARP control: Recent studies place FEN1 as a nuclease recruited to diverse DPC lesions by PARylation-dependent scaffolding, suggesting that flap-processing logic can be reused for DPC repair intermediates (sun2023flapendonuclease1 pages 9-11, saha2024parp1drivenrepairof pages 1-3).
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Repair-pathway cross-talk and regulation by protein interactions/PTMs: 2024 work on XPAโFEN1 binding and earlier mechanistic work on modification-driven partner switching (e.g., SUMOylation enabling interaction with checkpoint clamps) reinforce the view that FEN1โs pathway choice is heavily context- and interaction-dependent (krasikova2024doesthexpaโfen1 pages 1-2, xu2018sumo1modificationof pages 4-6).
8) Statistics and data highlights (recent studies)
- PCNA stimulation: PCNA increases FEN1 nuclease activity by ~10โ50ร in vitro (Tian et al., published Nov 2024, URL: https://doi.org/10.1038/s44318-024-00296-x) (tian2024structuralinsightinto pages 1-2).
- Cryo-EM structural resolution: Endogenous PCNAโFEN1 complexes resolved at 3.5โ3.8 ร (Tian et al., Nov 2024) (tian2024structuralinsightinto pages 4-6).
- OFM intermediate sizes: Okazaki primers ~30 nt total; short flaps typically ~2โ10 nt (Tian et al., Nov 2024) (tian2024structuralinsightinto pages 1-2).
- Zebrafish assay parameters: fen1 qPCR amplicon 138 bp with 100% PCR efficiency; larval exposures include DBP 0/0.5/5 ฮผM and MEHP/DEHP 0/10/25/50 ฮผM from 4 hpf (Lu et al., published Jan 2021, URL: https://doi.org/10.1016/j.ecoenv.2020.111525) (lu2021theoxidativestress pages 2-3).
- Zebrafish fen1 induction: fen1 is significantly upregulated in zebrafish qPCR panels (asterisk-marked significance in figure panels) following multiple exposure conditions in the same study (lu2021theoxidativestress media 0d94d88c, lu2021theoxidativestress media b881018e, lu2021theoxidativestress media 38921355, lu2021theoxidativestress media 1bd7b56f).
9) Practical applications and implementations relevant to fen1/FEN1
9.1 Zebrafish as a DNA repair/BER readout model (environmental DDR)
Zebrafish larvae are used as an in vivo vertebrate system to measure BER pathway gene responses including fen1 under chemical exposures interpreted as oxidative stressors, enabling integration of developmental outcomes with DNA repair pathway transcriptional activation (lu2021theoxidativestress pages 2-3, lu2021theoxidativestress media 0d94d88c).
9.2 Genome engineering strategy using FEN1โs structure recognition
FEN1โs flap-recognition property has been engineered into a programmable nuclease platform (SGN) that can cleave targets in zebrafish embryos, illustrating translational use of FEN1 biochemistry in a living vertebrate model (Xu et al., published Sep 2016, URL: https://doi.org/10.1186/s13059-016-1038-5) (xu2016analternativenovel pages 1-2).
9.3 Cancer/therapy-relevant frameworks (human-centric but mechanistically informative)
Recent reviews frame structure-specific nucleases (including FEN1) as targets for cancer therapy by leveraging their essentiality in replication stress and DNA repair networks, a mechanistic context that can inform zebrafish model design for DNA repair and chemical-genetic interactions (sun2024structurespecificnucleasesin pages 2-3).
10) Limitations and evidence gaps specific to Danio rerio fen1
Within the retrieved full-text set, there is limited direct zebrafish fen1 functional genetics (e.g., fen1 knockout phenotype, subcellular localization imaging, developmental tissue-specific expression atlases). The strongest zebrafish-specific evidence retrieved is transcript-level association with BER pathway induction under chemical stress and zebrafish usage as an in vivo platform for a FEN1-derived engineered nuclease (lu2021theoxidativestress pages 2-3, xu2016analternativenovel pages 1-2). Accordingly, the primary functional annotation for zebrafish fen1 is best supported by orthology-informed mechanism (PCNA-coordinated flap processing in OFM and LP-BER) plus zebrafish expression responsiveness in BER-relevant contexts (tian2024structuralinsightinto pages 1-2, xu2018sumo1modificationof pages 2-3, lu2021theoxidativestress pages 2-3).
Summary artifact
The following table consolidates enzymatic activities, substrates, regulators, and recent mechanistic advances relevant for functional annotation.
| FEN1 activity / context | Primary substrate(s) | Key partners / regulators | Representative 2023โ2024 mechanistic or structural findings | Quantitative details | Citations |
|---|---|---|---|---|---|
| Flap endonuclease during Okazaki fragment maturation | Short 5โฒ RNA/DNA flaps generated by Pol ฮด strand displacement on lagging-strand intermediates | PCNA; RNaseH2 | FEN1 is the primary nuclease for short 5โฒ flaps in OFM; cryo-EM captured endogenous PCNAโFEN1 and PCNAโFEN1โRNaseH2 assemblies in multiple primer-removal states, supporting the PCNA โtoolbeltโ model and indicating that RNaseH2 can promote FEN1-mediated flap cleavage through DNA conformational modulation; product release from FEN1 was identified as rate-limiting | PCNA can stimulate FEN1 activity by ~10โ50ร; Okazaki primers are ~30 nt total (8โ12 nt RNA + 10โ20 nt DNA); typical displaced short flaps are ~2โ10 nt; cryo-EM resolution 3.5โ3.8 ร | (tian2024structuralinsightinto pages 1-2, tian2024structuralinsightinto pages 4-6) |
| Structural basis of flap cleavage on PCNA | Nicked/flapped DNA with downstream duplex and 5โฒ flap | PCNA via PIP-box and IDCL interactions | Structures show one FEN1 bound to one PCNA protomer, with the FEN1 PIP-box inserted into the PCNA hydrophobic pocket; DNA adopts an L-shaped configuration; the cleaved 5โฒ flap remains transiently bound in an early post-catalytic state, explaining slow product release | One PCNA ring can potentially recruit up to 3 PIP-box proteins; downstream duplex ~12 bp; upstream duplex through the ring 14โ19 bp; only ~3 proximal flap nucleotides traceable; catalytic metal-binding residues include E158, E160, D179, D181 | (tian2024structuralinsightinto pages 1-2, tian2024structuralinsightinto pages 4-6) |
| Long-patch base excision repair (LP-BER) flap removal | Short DNA flaps produced during repair resynthesis after damaged-base removal | PCNA; BER machinery | FEN1 is a core LP-BER nuclease that removes repair flaps after strand displacement synthesis; recent reviews continue to place FEN1 as the canonical 5โฒ-flap nuclease linking BER and replication, with a two-metal active center characteristic of structure-specific nucleases | LP-BER flaps described as ~2โ20 nt; active site uses 2 Mg2+ ions | (krasikova2024doesthexpaโfen1 pages 1-2, sun2024structurespecificnucleasesin pages 2-3, xu2018sumo1modificationof pages 2-3) |
| 5โฒ exonuclease proofreading / ฮฑ-segment error editing | 5โฒ termini and misincorporated Pol ฮฑ-generated segments during lagging-strand synthesis | PCNA; mismatch-repair-associated factors | Beyond flap cutting, FEN1โs 5โฒ exonuclease activity contributes to editing/removal of Pol ฮฑ errors during Okazaki fragment maturation, helping prevent mutagenesis when nascent lagging strands are processed | No specific 2023โ2024 numeric measurement in retrieved text; activity explicitly distinguished from flap endonuclease and gap endonuclease functions | (xu2018sumo1modificationof pages 2-3, sun2023okazakifragmentmaturation pages 9-11) |
| Gap endonuclease / stalled fork & structured DNA processing | Gapped or structured DNA intermediates, including secondary structures at difficult-to-replicate regions | Rad9โRad1โHus1; SUMOylation; checkpoint signaling | FEN1โs GEN activity is implicated in processing stalled replication forks and DNA secondary structures; SUMO-1 modification promotes switching from replication-associated partners toward the 9-1-1 clamp to counter replication stress | Qualitative evidence in retrieved sources; no specific 2023โ2024 numeric value extracted | (xu2018sumo1modificationof pages 4-6, xu2018sumo1modificationof pages 2-3) |
| Replication-stress response / partner switching | Flap or fork-associated DNA at stalled replication sites | SUMO-1; Rad9โRad1โHus1; phosphorylation | DNA damage-induced sequential phosphorylation and SUMO-1 conjugation facilitate FEN1 interaction with HUS1, helping FEN1 act in repair rather than only canonical OFM; SUMO-defective FEN1 mutants are hypersensitive to fork-stalling agents | Triggering agents cited include UV, hydroxyurea, and mitomycin C; no precise fold-change reported in retrieved excerpt | (xu2018sumo1modificationof pages 4-6) |
| DPC repair: formaldehyde and TOP2-linked lesions | DPC-conjugated 5โฒ flaps, including BER-generated 5โฒ flaps and TOP2-DPC-associated flap substrates | PARP1; PARG; SPRTN; TDP2 | FEN1 can excise non-enzymatic FA-DPCs and enzymatic TOP2-DPCs from 5โฒ-flap-like structures; PARylation promotes recruitment rather than intrinsic catalytic enhancement, placing FEN1 in a PARP1/PARG-regulated DPC-repair axis parallel to SPRTN | Major PARylation site mapped to E285; nuclease-dead comparator D181A; no intrinsic activity increase detected after PARylation in vitro | (sun2023flapendonuclease1 pages 1-3, sun2023flapendonuclease1 pages 3-5, sun2023flapendonuclease1 pages 9-11) |
| DPC repair: TOP3A-DPC pathway choice | Persistent TOP3A-DPC intermediates | PARP1; ubiquitylation machinery; SPRTN/TDP2 | PARP1-driven PARylation recruits FEN1 to TOP3A-DPCs, while ubiquitylation supports an alternative proteolytic pathway; blocking PARylation reduces FEN1โTOP3A interaction and increases TOP3A-DPC burden, indicating PTM-controlled pathway choice | Persistent TOP3A-DPC model used catalytic mutant R364W; no additional quantitative structural values extracted | (saha2024parp1drivenrepairof pages 1-3) |
| NER-/R-loop-adjacent cross-talk | 5โฒ-flap substrates with repair gaps; R-loop-associated ssDNA | XPA; RPA | FEN1 forms ternary complexes with XPA and DNA, supporting possible roles beyond canonical BER/replication, including post-incision NER resynthesis or other repair processes; XPA moderately inhibits FEN1 catalytic activity in vitro | Tested DNA substrates carried a 31-nt 5โฒ flap with 3-, 10-, or 26-nt gaps | (krasikova2024doesthexpaโfen1 pages 1-2) |
| Cancer targeting / biomarker relevance | Replication/repair intermediates in stressed or HR-deficient tumor cells | PARP/PARG axis; EXO1; synthetic lethality frameworks | Recent work positions FEN1 as a vulnerability in tumors with defective PAR metabolism or HR deficiency; reviews frame structure-specific nucleases, including FEN1, as therapeutic targets, and PARG-deficient tumor cells show increased dependence on EXO1/FEN1-mediated repair | No single universal effect size given in retrieved excerpt; dependency highlighted in 2024 tumor models | (sun2024structurespecificnucleasesin pages 2-3) |
Table: This table summarizes the main biochemical activities of FEN1, their substrates, major cofactors/regulators, and recent 2023โ2024 mechanistic advances. It is useful for linking classical functional annotation to current structural biology and repair-pathway models.
References
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(lu2021theoxidativestress pages 2-3): Chunjiao Lu, Juanjuan Luo, Yao Liu, and Xiaojun Yang. The oxidative stress responses caused by phthalate acid esters increases mrna abundance of base excision repair (ber) genes in vivo and in vitro. Jan 2021. URL: https://doi.org/10.1016/j.ecoenv.2020.111525, doi:10.1016/j.ecoenv.2020.111525. This article has 55 citations and is from a domain leading peer-reviewed journal.
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(sun2024structurespecificnucleasesin pages 2-3): Haitao Sun, Megan Luo, Mian Zhou, Li Zheng, Hongzhi Li, R Steven Esworthy, and Binghui Shen. Structure-specific nucleases in genome dynamics and strategies for targeting cancers. Journal of Molecular Cell Biology, May 2024. URL: https://doi.org/10.1093/jmcb/mjae019, doi:10.1093/jmcb/mjae019. This article has 4 citations and is from a peer-reviewed journal.
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(xu2018sumo1modificationof pages 2-3): Xiaoli Xu, Rongyi Shi, Li Zheng, Zhigang Guo, Liangyan Wang, Mian Zhou, Ye Zhao, Bing Tian, Khue Truong, Yuan Chen, Binghui Shen, Yuejin Hua, and Hong Xu. Sumo-1 modification of fen1 facilitates its interaction with rad9โrad1โhus1 to counteract dna replication stress. Journal of Molecular Cell Biology, 10:460-474, Oct 2018. URL: https://doi.org/10.1093/jmcb/mjy047, doi:10.1093/jmcb/mjy047. This article has 23 citations and is from a peer-reviewed journal.
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(sun2023okazakifragmentmaturation pages 9-11): Haitao Sun, Lingzi Ma, Ya-Fang Tsai, Tharindu Abeywardana, Binghui Shen, and Li Zheng. Okazaki fragment maturation: dna flap dynamics for cell proliferation and survival. Mar 2023. URL: https://doi.org/10.1016/j.tcb.2022.06.014, doi:10.1016/j.tcb.2022.06.014. This article has 63 citations and is from a domain leading peer-reviewed journal.
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(sun2023flapendonuclease1 pages 9-11): Yilun Sun, Lisa M. Jenkins, Lara H. El Touny, Ukhyun Jo, Xi Yang, Tapan K. Maity, Liton K. Saha, Isabel Uribe, Sourav Saha, Shunichi Takeda, Anthony K.L. Leung, Ken Cheng, and Yves Pommier. Flap endonuclease 1 repairs dna-protein crosslinks via adp-ribosylation. bioRxiv, Oct 2023. URL: https://doi.org/10.1101/2023.10.19.563118, doi:10.1101/2023.10.19.563118. This article has 3 citations.
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(lu2021theoxidativestress media 0d94d88c): Chunjiao Lu, Juanjuan Luo, Yao Liu, and Xiaojun Yang. The oxidative stress responses caused by phthalate acid esters increases mrna abundance of base excision repair (ber) genes in vivo and in vitro. Jan 2021. URL: https://doi.org/10.1016/j.ecoenv.2020.111525, doi:10.1016/j.ecoenv.2020.111525. This article has 55 citations and is from a domain leading peer-reviewed journal.
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(sun2023flapendonuclease1 pages 1-3): Yilun Sun, Lisa M. Jenkins, Lara H. El Touny, Ukhyun Jo, Xi Yang, Tapan K. Maity, Liton K. Saha, Isabel Uribe, Sourav Saha, Shunichi Takeda, Anthony K.L. Leung, Ken Cheng, and Yves Pommier. Flap endonuclease 1 repairs dna-protein crosslinks via adp-ribosylation. bioRxiv, Oct 2023. URL: https://doi.org/10.1101/2023.10.19.563118, doi:10.1101/2023.10.19.563118. This article has 3 citations.
Artifacts
Citations
- lu2021theoxidativestress pages 2-3
- sun2024structurespecificnucleasesin pages 2-3
- sun2023okazakifragmentmaturation pages 9-11
- tian2024structuralinsightinto pages 1-2
- tian2024structuralinsightinto pages 4-6
- xu2016analternativenovel pages 1-2
- https://doi.org/10.1038/s44318-024-00296-x
- https://doi.org/10.1016/j.ecoenv.2020.111525
- https://doi.org/10.1186/s13059-016-1038-5
- https://doi.org/10.1016/j.ecoenv.2020.111525,
- https://doi.org/10.1093/jmcb/mjae019,
- https://doi.org/10.1093/jmcb/mjy047,
- https://doi.org/10.1016/j.tcb.2022.06.014,
- https://doi.org/10.3390/biom14070814,
- https://doi.org/10.1101/2023.10.19.563118,
- https://doi.org/10.1038/s44318-024-00296-x,
- https://doi.org/10.1016/j.celrep.2024.114522,
- https://doi.org/10.1186/s13059-016-1038-5,