{"gene":"XRN2","run_date":"2026-06-11T09:02:06","timeline":{"discoveries":[{"year":2004,"finding":"XRN2 acts as a 5'→3' exonuclease 'torpedo' that degrades the downstream RNA product of co-transcriptional cleavage (CoTC) at the beta-globin gene, resulting in transcriptional termination by RNA Pol II. The CoTC autocatalytic RNA provides a free 5' end that XRN2 recognizes to degrade the nascent transcript and chase down Pol II.","method":"siRNA knockdown of XRN2, in vitro transcription/cleavage assays, nuclear run-on assays","journal":"Nature","confidence":"High","confidence_rationale":"Tier 2 / Strong — functional KD with defined molecular readout, replicated in multiple subsequent studies across labs","pmids":["15565158"],"is_preprint":false},{"year":2007,"finding":"XRN2 physically associates with p54nrb/PSF and 3'-processing factors, accumulates at the 3' end of transcribed genes, and is recruited to the 3'-processing machinery via p54nrb/PSF. In vitro, XRN2 degrades the downstream RNA after poly(A) site cleavage (but is not required for the cleavage itself), and degradation is stimulated when coupled to cleavage. p54nrb knockdown reduces XRN2 recruitment and causes termination defects.","method":"Co-immunoprecipitation, in vitro 3'-processing assays, ChIP, siRNA knockdown","journal":"Genes & development","confidence":"High","confidence_rationale":"Tier 2 / Moderate — reciprocal interaction shown, in vitro activity assay, ChIP, and KD with functional readout in single lab with multiple orthogonal methods","pmids":["17639083"],"is_preprint":false},{"year":2011,"finding":"Senataxin resolves R-loop structures (RNA/DNA hybrids) that form behind elongating Pol II over G-rich pause sites downstream of poly(A) signals, and this resolution is required for XRN2 to access the 3' cleavage product and degrade it to promote Pol II termination.","method":"siRNA knockdown of senataxin and XRN2, R-loop immunofluorescence, nuclear run-on, ChIP","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 2 / Strong — epistatic placement of senataxin upstream of XRN2, multiple orthogonal methods, replicated in subsequent studies","pmids":["21700224"],"is_preprint":false},{"year":2010,"finding":"XRN2 plays a major role in mammalian pre-rRNA maturation (generating 5' ends of 5.8S and 28S rRNAs) and in degradation of aberrant/discarded pre-rRNA species via 5'→3' exonuclease activity. siRNA knockdown causes accumulation of precursors with 5' extensions.","method":"siRNA knockdown of Xrn2 in mouse cells, Northern blotting, primer extension analysis","journal":"Nucleic acids research","confidence":"High","confidence_rationale":"Tier 2 / Moderate — clean KD with specific molecular readouts using multiple RNA analysis methods","pmids":["21036871"],"is_preprint":false},{"year":2012,"finding":"Decapping proteins Edc3, Dcp1a, and Dcp2 and the termination factor TTF2 co-immunoprecipitate with XRN2. Knockdown of decapping factors or XRN2/TTF2 redistributes Pol II away from the TSS toward upstream and downstream distal positions, indicating that coupled decapping of nascent transcripts and XRN2-mediated premature termination limits bidirectional Pol II elongation.","method":"Co-immunoprecipitation, ChIP-seq, siRNA knockdown","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 2 / Moderate — reciprocal Co-IP plus genome-wide ChIP-seq with KD phenotype, multiple orthogonal methods in single lab","pmids":["22483619"],"is_preprint":false},{"year":2012,"finding":"Microprocessor (Drosha/Dgcr8) orchestrates recruitment of Setx and XRN2 to the HIV-1 promoter. Cleavage of the stem-loop RNA TAR initiates RNAPII pausing and premature termination at the HIV-1 promoter, with XRN2 acting cooperatively with Rrp6 downstream of microprocessor cleavage.","method":"ChIP-seq, siRNA knockdown, co-immunoprecipitation, transcriptional reporter assays","journal":"Cell","confidence":"High","confidence_rationale":"Tier 2 / Moderate — genome-wide ChIP-seq combined with functional KD and mechanistic dissection of pathway order","pmids":["22980978"],"is_preprint":false},{"year":2012,"finding":"XRN2 associates with nascent pre-mRNA and co-transcriptionally degrades aberrantly processed pre-mRNAs (e.g., splicing or 3'-processing mutants). XRN2 also degrades many endogenous pre-mRNAs when processing is inhibited by Spliceostatin A.","method":"ChIP, RNA immunoprecipitation, siRNA knockdown, RT-PCR, Northern blotting","journal":"The EMBO journal","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — ChIP and RIP with KD, but single lab","pmids":["22522706"],"is_preprint":false},{"year":2015,"finding":"XRN2 uses a torpedo mechanism that operates genome-wide: a dominant-negative catalytically inactive Xrn2 mutant delayed termination at most poly(A) sites and some histone and snRNA genes. Kinetic competition between XRN2 exonuclease and Pol II elongation rate determines the location of termination—slow elongation shifts termination upstream and fast elongation extends it downstream.","method":"Dominant-negative XRN2 mutant expression, Pol II rate mutants, PRO-seq/GRO-seq genome-wide nascent RNA profiling","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 2 / Strong — genome-wide functional assay with mechanistic mutants, kinetic competition demonstrated, replicated conceptually across multiple labs","pmids":["26474067"],"is_preprint":false},{"year":2016,"finding":"CDK9 (P-TEFb) phosphorylates XRN2 at Thr439 in vivo and in vitro. This phosphorylation enhances XRN2 enzymatic activity on synthetic substrates. Mutation of Thr439 to alanine (non-phosphorylatable) impairs XRN2 chromatin localization and increases readthrough transcription, phenocopying CDK9 inhibition.","method":"Chemical genetic substrate identification, in vitro kinase assay with purified proteins, phosphomimetic/phospho-null mutagenesis, ChIP, nascent RNA analysis","journal":"Genes & development","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro kinase assay plus mutagenesis plus in vivo functional validation in single lab with multiple orthogonal methods","pmids":["26728557"],"is_preprint":false},{"year":2016,"finding":"XRN2 undergoes DNA damage-inducible nuclear re-localization, co-localizing with 53BP1 and R-loops in a transcription- and R-loop-dependent process. XRN2 loss leads to increased R-loops, genomic instability, replication stress, DSBs, and hypersensitivity to DNA damaging agents. DSBs from XRN2 loss occur at transcriptional pause sites, and XRN2-deficient cells show an R-loop- and transcription-dependent delay in DSB repair after ionizing radiation.","method":"Immunofluorescence, co-localization microscopy, R-loop detection (S9.6 antibody), siRNA knockdown, comet assay, gamma-H2AX staining, clonogenic survival assays","journal":"PLoS genetics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple readouts in single lab but primarily KD/localization-based without in vitro reconstitution","pmids":["27437695"],"is_preprint":false},{"year":2018,"finding":"Conditional depletion of XRN2 via gene editing reveals a clear general role in cotranscriptional degradation of 3'-flanking region RNA and transcriptional termination genome-wide. XRN2's effect on termination requires prior RNA cleavage by CPSF73. XRN2 plays no significant role in histone or snRNA gene termination. CPSF73 loss causes more extensive readthrough than XRN2 loss, indicating CPSF73 has a more foundational role.","method":"Auxin-inducible degron conditional depletion, mNET-seq genome-wide, catalytically inactive CPSF73 complementation","journal":"Genes & development","confidence":"High","confidence_rationale":"Tier 2 / Strong — conditional depletion with genome-wide high-resolution nascent RNA mapping plus mutant complementation, rigorous epistasis","pmids":["29432121"],"is_preprint":false},{"year":2014,"finding":"XRN2 protects HCV RNA from degradation in the cytoplasm is counteracted by miR-122: Xrn2 depletion increases HCV RNA accumulation, while overexpression diminishes it by affecting viral RNA stability (not translation or replication). During miR-122 sequestration, Xrn2 depletion restored HCV RNA abundance.","method":"siRNA knockdown, overexpression, luciferase reporter assays, RNA stability measurements","journal":"Cell host & microbe","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple complementary experiments (KD, OE, epistasis with miR-122), single lab","pmids":["25121753"],"is_preprint":false},{"year":2017,"finding":"NKRF (NF-κB repressing factor) forms a pre-ribosomal subcomplex with DHX15 and XRN2, binds transcribed spacer regions of pre-rRNA (shown by CRAC), recruits XRN2 to nucleolar pre-ribosomal complexes, and is required for an early pre-rRNA cleavage step (A'). Depletion of NKRF or XRN2 impairs A' cleavage and causes accumulation of excised pre-rRNA spacer fragments.","method":"Co-immunoprecipitation, UV crosslinking and cDNA analysis (CRAC), siRNA knockdown, Northern blotting, sucrose gradient sedimentation","journal":"Nucleic acids research","confidence":"High","confidence_rationale":"Tier 2 / Moderate — reciprocal Co-IP, direct RNA crosslinking, KD with specific processing readouts, multiple orthogonal methods","pmids":["28115624"],"is_preprint":false},{"year":2014,"finding":"In C. elegans, PAXT-1 (R05D11.6) stabilizes XRN2 protein levels and is required for miRNA turnover activity. A truncated PAXT-1 retaining only the DUF3469/XTBD domain suffices to restore viability, elevate XRN2 levels, and bind XRN2. Human CDKN2AIP/CARF and NKRF interact with XRN2 through this same XTBD domain.","method":"TALEN-mediated genome editing, co-immunoprecipitation, western blotting, worm survival assays, in vivo complementation","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 2 / Moderate — genome editing KO, direct binding shown, domain sufficiency demonstrated in vivo, conservation tested in human proteins","pmids":["24462208"],"is_preprint":false},{"year":2016,"finding":"The XTBD (XRN2-binding domain) from PAXT-1 stably interconnects two XRN2 domains through numerous interacting residues (crystal structure). Mutation of a single critical residue disrupts XTBD-XRN2 complexes in vitro and recapitulates paxt-1-null phenotypes in vivo. Vertebrate XTBD-containing proteins (CDKN2AIPNL) bind XRN2 in vitro and can substitute for PAXT-1 in C. elegans. In the absence of substrate, complex formation with PAXT-1 serves to preserve XRN2 stability.","method":"X-ray crystallography, in vitro binding assays, site-directed mutagenesis, C. elegans genetic complementation","journal":"Nature structural & molecular biology","confidence":"High","confidence_rationale":"Tier 1 / Moderate — crystal structure plus mutagenesis plus in vivo functional validation with single critical residue identified","pmids":["26779609"],"is_preprint":false},{"year":2012,"finding":"In Tetrahymena, the Piwi protein Twi12 binds mature 3' tRNA fragments and assembles a complex with nuclear exonuclease Xrn2. Twi12 stabilizes and localizes Xrn2 to the nucleus, and stimulates its exonuclease activity. Loss of Twi12 or Xrn2 causes rRNA processing defects. Twi12 sRNA binding is required for nuclear import of the complex.","method":"Co-immunoprecipitation, sRNA sequencing, ribosome profiling, northern blotting, localization studies, Xrn2 activity assays","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 2 / Moderate — direct complex assembly shown, functional stimulation demonstrated, nuclear import requirement shown, multiple orthogonal methods","pmids":["23084833"],"is_preprint":false},{"year":2015,"finding":"CARF (collaborator of ARF) directly associates with XRN2 and regulates its subcellular distribution: CARF overexpression increases XRN2 in the nucleoplasm and suppresses pre-rRNA processing, causing accumulation of 5'-extended 45S/47S pre-rRNA; CARF knockdown increases XRN2 in the nucleolar fraction. This phenocopies XRN2 knockdown in the nucleolus.","method":"Co-immunoprecipitation, cell fractionation, immunocytochemistry, western blotting, northern blotting, siRNA knockdown/overexpression","journal":"Nucleic acids research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct interaction, localization shift, and rRNA processing phenotype shown, but single lab","pmids":["26531822"],"is_preprint":false},{"year":2013,"finding":"hnRNPK co-immunoprecipitates with XRN2 in nuclear extracts; hnRNPK knockdown decreases XRN2 recruitment along EGR1 and downstream of its poly(A) signal (ChIP-seq), and increases pre-RNA read-through downstream of the EGR1 polyadenylation site, suggesting hnRNPK recruits XRN2 to gene loci to regulate termination.","method":"ChIP-seq, siRNA knockdown, co-immunoprecipitation with mass spectrometry, RT-PCR","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — ChIP-seq plus Co-IP and KD functional readout, single lab","pmids":["23857582"],"is_preprint":false},{"year":2019,"finding":"Rapid depletion of XRN2 (using degron technology) reveals that XRN2 loss uncovers different mechanisms for early termination of transcription from protein-coding gene promoters, and that XRN2 has little activity on exosome (DIS3/EXOSC10) substrates.","method":"Auxin-inducible degron rapid protein depletion, RNA-seq, PRO-seq","journal":"Cell reports","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — rapid conditional depletion with genome-wide readout, single lab","pmids":["30840897"],"is_preprint":false},{"year":2022,"finding":"XRN2 is recruited to preinitiation complexes and travels to 3' gene ends. Mapping of 5'-PO4 ends using catalytically inactive Xrn2(D235A) shows XRN2 loading sites ~2–20 bases downstream of CPSF73 cleavage at polyA sites and histone 3' ends, indicating handoff from CPSF73 to XRN2. A similar handoff occurs at tRNA 3' ends after RNase Z cleavage. XRN2 also degrades sense and antisense nascent RNA within a few bases of the TSS, revealing widespread promoter-proximal premature termination by the torpedo mechanism.","method":"5'-PO4 nascent RNA mapping with active-site mutant (Xrn2 D235A), eNET-seq, ChIP, PRO-seq","journal":"Genes & development","confidence":"High","confidence_rationale":"Tier 1 / Moderate — active-site mutant substrate trapping with genome-wide nascent RNA mapping, rigorous mechanistic design","pmids":["36396340"],"is_preprint":false},{"year":2022,"finding":"NMR studies reveal that Xrn2 is highly dynamic around its catalytic center in the apo state, and substrate plus magnesium shifts the conformational equilibrium toward an active state. A mutation that attenuates these dynamics also reduces catalytic activity, establishing that conformational dynamics are integral to the catalytic mechanism.","method":"Fluorine and methyl-TROSY NMR spectroscopy, in vitro RNA degradation assays, mutagenesis","journal":"Nature chemical biology","confidence":"High","confidence_rationale":"Tier 1 / Moderate — NMR structure/dynamics plus mutagenesis plus in vitro activity assay, orthogonal methods in single rigorous study","pmids":["36008487"],"is_preprint":false},{"year":2023,"finding":"RNF8 ubiquitylates XRN2, facilitating its recruitment to R-loop-prone genomic loci. RNF8 deficiency decreases XRN2 occupancy at R-loop-prone sites, promoting R-loop accumulation and transcription-replication collisions, leading to genomic instability in BRCA1-mutant cells.","method":"Co-immunoprecipitation, ubiquitylation assays, ChIP, R-loop detection (DRIP), genome stability assays, mouse mammary tumorigenesis model","journal":"Nucleic acids research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — ubiquitylation demonstrated, ChIP showing reduced recruitment, functional consequence shown, single lab","pmids":["37697435"],"is_preprint":false},{"year":2020,"finding":"XRN2-mediated R-loop resolution is required for Ku70 binding to DNA ends and initiation of NHEJ repair. XRN2 loss also decreases homologous recombination repair, but this is not restored by RNaseH1 overexpression, indicating that unregulated transcription (not just R-loops) inhibits HR.","method":"siRNA knockdown, RNaseH1 overexpression, Ku70 ChIP, DR-GFP and EJ5-GFP HR/NHEJ reporter assays","journal":"Cancers","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — epistasis with RNaseH1 plus DSB repair reporter assays, mechanistic dissection in single lab","pmids":["32645903"],"is_preprint":false},{"year":2020,"finding":"Genome-wide DRIP-seq reveals that XRN2 depletion causes hundreds to thousands of R-loop gains preferentially at highly transcribed genes at transcription termination sites. XRN2, DDX5, and PRMT5 share many R-loop gain loci at termination sites, but DDX5 has unique R-loop gain peaks near TSS not overlapping siXRN2, indicating distinct roles.","method":"DRIP-seq (genome-wide R-loop mapping), siRNA knockdown","journal":"Life science alliance","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genome-wide direct R-loop mapping with KD, single lab","pmids":["32747416"],"is_preprint":false},{"year":2016,"finding":"In fission yeast, Dhp1/Xrn2 cooperates with RNA elimination factors to promote premature termination at meiotic genes and facilitate facultative heterochromatin formation. Dhp1 also interacts with the Clr4/Suv39h methyltransferase complex and acts directly to nucleate heterochromatin.","method":"Genetic epistasis, ChIP, co-immunoprecipitation, reporter gene silencing assays in S. pombe","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic epistasis plus biochemical interaction plus silencing assays, fission yeast ortholog","pmids":["26631744"],"is_preprint":false},{"year":2022,"finding":"XRN2 promotes recruitment of Sam68 to target transcripts, where the Sam68/XRN2 complex competes with CPSF for binding to strong distal polyadenylation signals, thereby promoting usage of suboptimal proximal polyadenylation signals and 3' UTR shortening.","method":"Co-immunoprecipitation, RNA immunoprecipitation, CLIP-seq, siRNA knockdown, poly(A)-seq transcriptome profiling","journal":"Nature structural & molecular biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — reciprocal Co-IP, CLIP-seq, and transcriptome-wide APA profiling with KD, single lab","pmids":["36344846"],"is_preprint":false},{"year":2016,"finding":"In C. elegans, Nkx2-5 deficiency affects Xrn2 binding to target loci and results in increased RNAPII occupancy and expression of mRNAs with long 3' UTRs from heart development genes. Genetic interaction (double heterozygous Nkx2-5+/−; Xrn2+/−) causes ventricular septum defects not seen in single heterozygotes, establishing that Nkx2-5 and Xrn2 cooperate in regulating alternative polyadenylation during heart development.","method":"ChIP, siRNA knockdown, genetic compound heterozygotes in mice, 3'-seq for APA analysis","journal":"eLife","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic epistasis in vivo plus ChIP showing XRN2 mis-recruitment, single lab","pmids":["27331609"],"is_preprint":false},{"year":2014,"finding":"In C. elegans, XRN2 loss of function (null or catalytic-dead) causes molting defect and larval arrest, demonstrating that XRN2 catalytic activity is essential for development. XRN2 has specificity for a subset of miRNAs in vivo—some rapidly decaying miRNAs are stabilized by XRN2 loss while others continue to decay, indicating XRN2-independent decay pathways for certain miRNAs.","method":"Conditional allele engineering (temperature-sensitive), null mutation, small RNA sequencing, miRNA stability assays","journal":"Nucleic acids research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — conditional allele with specific molecular readout for miRNA substrates, single lab","pmids":["24445807"],"is_preprint":false},{"year":2015,"finding":"Nuclear XRN2 degrades the 3' fragments of pre-mRNA generated by RNase H1-mediated cleavage of ASO-targeted transcripts from their 5' ends, while XRN1 is responsible for cytoplasmic mRNA fragment degradation after siRNA-mediated cleavage.","method":"siRNA knockdown of XRN1 and XRN2, northern blotting for cleavage fragment detection, nuclear/cytoplasmic fractionation","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — KD with specific fragment detection, single lab, single method set","pmids":["26159921"],"is_preprint":false},{"year":2011,"finding":"NPGPx covalently binds to XRN2 upon non-targeting siRNA stress and facilitates XRN2-mediated removal of accumulated non-targeting siRNA, relieving cellular stress.","method":"Co-immunoprecipitation, covalent crosslinking assay, siRNA accumulation measurement, cell growth assays","journal":"Nucleic acids research","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single Co-IP/covalent interaction claim, single lab, limited mechanistic follow-up","pmids":["21908404"],"is_preprint":false},{"year":2022,"finding":"CAPRIN1 promotes degradation of developmental transcripts during early ESC differentiation via XRN2. Upon differentiation, XRN2 localizes to the nucleus and co-localizes with CAPRIN1 in small RNA granules in a CAPRIN1-dependent manner, identifying CAPRIN1 as a factor that recruits XRN2 to specific RNA targets.","method":"CAPRIN1 knockout, RIP-seq, SLAM-seq, XRN2 co-immunoprecipitation/interactome, immunofluorescence co-localization","journal":"Developmental cell","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — RIP-seq plus SLAM-seq kinetics plus Co-IP interactome and localization, single lab","pmids":["36495875"],"is_preprint":false},{"year":2020,"finding":"XRN2 interacts with DNA repair/replication proteins including Ku70-Ku80, DNA-PKcs, PARP1, and MCM2-7 as shown by tandem affinity purification-mass spectrometry. XRN2 depletion hyperactivates PARP1 activity, and combined XRN2 depletion and PARP1 inhibition results in synthetic lethality.","method":"Tandem affinity purification-mass spectrometry (TAP-MS), Co-IP, PARP1 activity assay, siRNA knockdown, clonogenic survival, flow cytometry","journal":"Scientific reports","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — TAP-MS interactome plus functional synthetic lethality validation, single lab","pmids":["32859985"],"is_preprint":false},{"year":2023,"finding":"XRN2 regulates TERRA RNA stability; XRN2 depletion in ALT-positive cancer cells increases TERRA R-loops and exacerbates ALT activity, establishing XRN2 as a key determinant of TERRA metabolism at telomeres.","method":"siRNA knockdown, northern blotting for TERRA, DRIP-qPCR for R-loops, ALT-associated PML body foci quantification","journal":"FEBS letters","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single KD with functional readout, limited mechanistic detail, single lab","pmids":["37191774"],"is_preprint":false},{"year":2024,"finding":"Structural characterization of the Xrn2/Rat1-Rai1-Rtt103 torpedo termination complex from S. cerevisiae and C. thermophilum reveals conserved protein core folds but variable interaction interfaces: in the mesophile, Rtt103 uses an unstructured region to augment a Rai1 β-sheet, while in the thermophile Rtt103 binds a C-terminal Rai1 helix via a CTD-interacting domain with α-helical fold.","method":"Cryo-EM, X-ray crystallography, structural biology","journal":"Structure","confidence":"Medium","confidence_rationale":"Tier 1 / Weak — structural determination but limited functional mutagenesis validation reported in abstract, single study","pmids":["39657659"],"is_preprint":false},{"year":2020,"finding":"Full-length NKRF contains an N-terminal XTBD (XRN2-binding domain) encoded from an alternative upstream AUG start codon; this XTBD is essential for XRN2 retention in the nucleolus. NKRF is tethered in the nucleolus by binding rRNA and controls spatial distribution of XRN2 between nucleoplasm and nucleolus to regulate early pre-rRNA processing.","method":"Alternative start codon identification, co-immunoprecipitation, immunofluorescence, subcellular fractionation, domain deletion mutagenesis","journal":"The Biochemical journal","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — novel XTBD domain identified and functionally validated with localization and interaction data, single lab","pmids":["32011671"],"is_preprint":false},{"year":2025,"finding":"HELQ helicase interacts with XRN2 and cooperates with it in R-loop resolution: HELQ unwinds R-loops (requires ATPase activity) and is functionally coordinated with XRN2-mediated RNA digestion, shown both in cells and in vitro.","method":"Co-immunoprecipitation, in vitro helicase and exonuclease assays, R-loop detection in cells, siRNA/inhibitor experiments","journal":"Open biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vitro functional assay plus cell-based interaction and R-loop resolution, single lab","pmids":["39965657"],"is_preprint":false},{"year":2026,"finding":"XRN2 degrades hypomethylated (m1A-lacking) tRNA-iMet in human cells: acute loss of TRMT6/61A leads to rapid XRN2-dependent degradation of tRNA-iMet, reducing global protein synthesis. XRN2 inhibition rescues tRNA-iMet levels and reverses growth defects in TRMT6/61A-depleted cells.","method":"dTAG rapid depletion system, tRNA-seq, pulse-chase tRNA stability measurements, XRN2 knockdown/inhibition complementation assays","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — conditional depletion with kinetic measurements and rescue validation, but preprint and single lab","pmids":["42239164"],"is_preprint":true},{"year":2025,"finding":"XRN2 mediates accelerated decay of m7G-hypomodified tRNAs under physiological (non-stress) conditions: XRN2 knockdown restores tRNA levels diminished by METTL1 depletion. Partial loss of Drosophila XRN2 ortholog Rat1 genetically rescues male sterility of mettl1 mutants, establishing a conserved constitutive rapid tRNA decay pathway.","method":"siRNA knockdown of XRN2, conditional protein knockdown with time-resolved tRNA decay kinetics, Drosophila genetic epistasis","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — conditional depletion with kinetic decay measurements plus in vivo genetic epistasis across species, but preprint","pmids":["bio_10.1101_2025.11.05.686800"],"is_preprint":true},{"year":2017,"finding":"XRN2 accelerates maturation of pre-miR-10a by binding to the precursor miRNA in a DICER-independent manner, promoting its maturation and thereby inducing EMT and metastasis in lung cancer.","method":"Co-immunoprecipitation/pulldown of XRN2 with pre-miR-10a, in vitro processing assays, overexpression and knockdown, in vivo metastasis assays","journal":"Oncogene","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single pulldown and processing assay, unusual proposed mechanism (XRN2 as miRNA maturation factor rather than degradase), single lab without independent replication","pmids":["28319071"],"is_preprint":false}],"current_model":"XRN2 is a nuclear 5'→3' exoribonuclease that promotes RNA Pol II transcription termination genome-wide via the 'torpedo' mechanism—loading onto 5'-phosphate RNA ends generated by CPSF73 cleavage at poly(A) sites and degrading the remaining nascent transcript to chase down elongating Pol II—a process regulated by CDK9-mediated phosphorylation at Thr439 and facilitated by cofactors including p54nrb/PSF, senataxin (which resolves inhibitory R-loops), and XTBD-domain proteins (PAXT-1/NKRF/CARF) that stabilize and localize XRN2; it also processes pre-rRNA (5.8S and 28S maturation), degrades aberrant pre-mRNAs co-transcriptionally, turns over specific miRNAs and tRNAs, resolves R-loops to prevent genomic instability and enable DSB repair, and regulates alternative polyadenylation."},"narrative":{"mechanistic_narrative":"XRN2 is a nuclear 5'→3' exoribonuclease that enforces RNA polymerase II transcription termination genome-wide through the 'torpedo' mechanism: it loads onto the 5'-phosphate RNA end generated by CPSF73 cleavage at poly(A) sites and degrades the downstream nascent transcript to chase down and evict elongating Pol II [PMID:15565158, PMID:29432121, PMID:36396340]. Mapping of XRN2 loading sites with a catalytically inactive mutant places handoff a few bases downstream of CPSF73 cleavage at poly(A) and histone 3' ends, and an analogous handoff occurs at tRNA 3' ends after RNase Z cleavage [PMID:36396340]; XRN2 also degrades sense and antisense transcripts near the TSS to effect widespread promoter-proximal premature termination [PMID:36396340, PMID:22483619]. The position of termination is set by kinetic competition between XRN2 exonuclease progression and Pol II elongation rate [PMID:26474067], and access to the cleaved product requires resolution of R-loops over G-rich pause sites by senataxin [PMID:21700224]. XRN2 catalytic activity and chromatin loading are enhanced by CDK9/P-TEFb phosphorylation at Thr439 [PMID:26728557], its recruitment to gene 3' ends is mediated by interacting factors including p54nrb/PSF and hnRNPK [PMID:17639083, PMID:23857582], and conformational dynamics around its catalytic center are intrinsic to its degradation activity [PMID:36008487]. Beyond termination, XRN2 carries out pre-rRNA maturation—generating 5' ends of 5.8S and 28S rRNA and executing an early A' cleavage step within an NKRF/DHX15 pre-ribosomal subcomplex [PMID:21036871, PMID:28115624]. XRN2 protein stability and nucleoplasm/nucleolus partitioning are controlled by XTBD-domain proteins (PAXT-1, NKRF, CARF/CDKN2AIP), which dock onto and bridge two XRN2 domains [PMID:24462208, PMID:26779609, PMID:26531822, PMID:32011671]. XRN2 additionally degrades aberrantly processed nascent pre-mRNAs co-transcriptionally [PMID:22522706], turns over specific miRNAs and hypomodified tRNAs [PMID:24445807, PMID:bio_10.1101_2025.11.05.686800], resolves R-loops to suppress genomic instability and enable DSB repair [PMID:27437695, PMID:32645903], and shapes alternative polyadenylation [PMID:36344846].","teleology":[{"year":2004,"claim":"Established the foundational 'torpedo' model—that a 5'→3' exonuclease degrades the downstream cleavage product to terminate Pol II transcription—answering how termination is mechanistically coupled to nascent RNA cleavage.","evidence":"siRNA knockdown of XRN2 with in vitro cleavage and nuclear run-on assays at the beta-globin gene","pmids":["15565158"],"confidence":"High","gaps":["Demonstrated at a single gene rather than genome-wide","Did not define how XRN2 is recruited to the 3'-processing site"]},{"year":2007,"claim":"Identified how XRN2 is physically delivered to gene 3' ends, linking it to the cleavage/polyadenylation machinery via p54nrb/PSF.","evidence":"Co-IP, in vitro 3'-processing assays, ChIP and siRNA knockdown","pmids":["17639083"],"confidence":"High","gaps":["XRN2 not required for the cleavage step itself","Recruitment mechanism beyond p54nrb/PSF unresolved"]},{"year":2010,"claim":"Extended XRN2 function beyond termination to ribosome biogenesis, showing it generates mature rRNA 5' ends and clears aberrant pre-rRNA.","evidence":"siRNA knockdown in mouse cells with Northern blotting and primer extension","pmids":["21036871"],"confidence":"High","gaps":["Did not identify the nucleolar recruitment factors","Relationship to termination role not addressed"]},{"year":2011,"claim":"Defined a prerequisite for torpedo termination—senataxin must resolve R-loops behind paused Pol II so XRN2 can access the cleavage product.","evidence":"siRNA knockdown of senataxin and XRN2 with R-loop IF, nuclear run-on and ChIP","pmids":["21700224"],"confidence":"High","gaps":["In vitro reconstitution of the senataxin–XRN2 handoff not shown","Generality across genes not established at this stage"]},{"year":2012,"claim":"Showed XRN2 termination is not restricted to gene 3' ends but limits bidirectional/promoter-proximal Pol II elongation through coupling to decapping and TTF2, and operates at the HIV-1 promoter downstream of Microprocessor cleavage.","evidence":"Co-IP, ChIP-seq and siRNA knockdown (decapping factors/TTF2; Drosha/DGCR8/Setx)","pmids":["22483619","22980978"],"confidence":"High","gaps":["Direct vs indirect interactions with decapping factors not fully resolved","Substrate 5' end chemistry at promoters not mapped"]},{"year":2012,"claim":"Demonstrated XRN2 surveys nascent pre-mRNA and co-transcriptionally degrades transcripts that fail splicing or 3'-processing, broadening its role to RNA quality control.","evidence":"ChIP, RIP, siRNA knockdown, RT-PCR and Northern blotting with Spliceostatin A","pmids":["22522706"],"confidence":"Medium","gaps":["Single lab","Recognition of aberrant transcripts mechanistically undefined"]},{"year":2014,"claim":"Identified the XTBD-domain protein family (PAXT-1 and human CARF/NKRF homologs) as conserved factors that bind XRN2 and stabilize the protein, defining a post-translational control layer.","evidence":"TALEN editing, Co-IP, complementation and survival assays in C. elegans","pmids":["24462208"],"confidence":"High","gaps":["Structural basis of XTBD–XRN2 binding not yet resolved","Whether stabilization affects substrate selection unclear"]},{"year":2015,"claim":"Showed XRN2 turns over specific RNA substrates in trans—nuclear ASO/RNase H1-generated pre-mRNA 3' fragments—distinguishing its nuclear role from cytoplasmic XRN1.","evidence":"siRNA knockdown of XRN1/XRN2 with fragment Northern blotting and fractionation","pmids":["26159921"],"confidence":"Medium","gaps":["Single method set","Endogenous physiological substrates of this activity not defined"]},{"year":2015,"claim":"Demonstrated that XTBD protein CARF controls XRN2 nucleoplasm/nucleolus partitioning and thereby tunes pre-rRNA processing.","evidence":"Co-IP, cell fractionation, immunocytochemistry and KD/overexpression with Northern blotting","pmids":["26531822"],"confidence":"Medium","gaps":["Single lab","Signal triggering CARF-dependent relocalization unknown"]},{"year":2015,"claim":"Established a torpedo-independent function—nuclear stabilization of cytoplasmic HCV RNA antagonized by miR-122—indicating XRN2 substrate effects can be both degradative and protective in viral RNA metabolism.","evidence":"siRNA knockdown, overexpression, luciferase reporters and RNA stability assays","pmids":["25121753"],"confidence":"Medium","gaps":["Mechanism of XRN2-mediated protection vs degradation unclear","Single lab"]},{"year":2015,"claim":"Proved the torpedo operates genome-wide and that termination position is governed by kinetic competition between XRN2 and Pol II elongation rate.","evidence":"Dominant-negative catalytic-dead XRN2 with Pol II rate mutants and PRO-seq/GRO-seq","pmids":["26474067"],"confidence":"High","gaps":["Exact handoff coordinates from CPSF73 not yet mapped","Why histone/snRNA genes show partial dependence unresolved"]},{"year":2016,"claim":"Identified CDK9/P-TEFb phosphorylation of XRN2 at Thr439 as a regulatory switch enhancing activity and chromatin loading, linking elongation control kinases to termination.","evidence":"Chemical-genetic substrate ID, in vitro kinase assay, phospho-mutant mutagenesis, ChIP and nascent RNA analysis","pmids":["26728557"],"confidence":"High","gaps":["Whether phosphorylation alters substrate affinity vs catalysis not dissected","Additional regulatory phosphosites unexplored"]},{"year":2016,"claim":"Provided the structural basis for XTBD-mediated XRN2 stabilization, showing the domain bridges two XRN2 lobes and that a single residue mutation abolishes the complex and phenocopies the null.","evidence":"X-ray crystallography, in vitro binding, mutagenesis and C. elegans complementation","pmids":["26779609"],"confidence":"High","gaps":["Did not resolve full-length XRN2 catalytic architecture","Functional consequence of stabilization on individual substrates not mapped"]},{"year":2016,"claim":"Linked XRN2 to genome maintenance—its loss elevates R-loops, drives DSBs at transcriptional pause sites, and delays DSB repair, integrating its RNA-processing role with DNA stability.","evidence":"IF/co-localization with 53BP1, S9.6 R-loop detection, comet/γH2AX assays and clonogenic survival","pmids":["27437695"],"confidence":"Medium","gaps":["No in vitro reconstitution of R-loop resolution by XRN2","Direct vs indirect contribution to repair unresolved"]},{"year":2017,"claim":"Assembled XRN2 into an NKRF/DHX15 pre-ribosomal subcomplex that binds pre-rRNA spacers and executes the early A' cleavage step, mechanistically grounding the rRNA processing role.","evidence":"Co-IP, CRAC, siRNA knockdown, Northern blotting and sucrose gradients","pmids":["28115624"],"confidence":"High","gaps":["Catalytic basis of A' cleavage by XRN2 vs accessory factors unclear","Coordination with DHX15 helicase activity undefined"]},{"year":2018,"claim":"Used rapid conditional depletion and CPSF73 epistasis to establish that genome-wide XRN2-dependent termination strictly requires prior CPSF73 cleavage, while CPSF73 has a more foundational role and XRN2 is dispensable at histone/snRNA genes.","evidence":"Auxin-inducible degron depletion, mNET-seq and catalytic-inactive CPSF73 complementation","pmids":["29432121"],"confidence":"High","gaps":["What terminates histone/snRNA genes independently of XRN2 unresolved","Residual readthrough mechanisms not defined"]},{"year":2019,"claim":"Distinguished XRN2-dependent early termination from exosome activity, showing XRN2 has little role on DIS3/EXOSC10 substrates.","evidence":"Auxin-inducible degron rapid depletion with RNA-seq and PRO-seq","pmids":["30840897"],"confidence":"Medium","gaps":["Single lab","Partition of substrates between torpedo and exosome incompletely mapped"]},{"year":2020,"claim":"Mapped XRN2 R-loop substrates genome-wide and showed its loss causes R-loop gains preferentially at termination sites of highly transcribed genes, distinguishing it from DDX5/PRMT5.","evidence":"DRIP-seq with siRNA knockdown","pmids":["32747416"],"confidence":"Medium","gaps":["Single lab","Whether R-loop resolution is degradative or via partner helicases not established"]},{"year":2020,"claim":"Connected XRN2 R-loop resolution to DSB repair pathway choice, showing it is required for Ku70 loading and NHEJ initiation and supports HR independently of R-loops.","evidence":"siRNA knockdown, RNaseH1 overexpression, Ku70 ChIP and DR-GFP/EJ5-GFP reporters","pmids":["32645903"],"confidence":"Medium","gaps":["Direct physical contribution of XRN2 to repair complexes unclear","Single lab"]},{"year":2020,"claim":"Defined an XRN2 interactome with DNA repair/replication machinery and revealed a synthetic-lethal relationship with PARP1 inhibition, suggesting therapeutic context.","evidence":"TAP-MS, Co-IP, PARP1 activity assay, KD with clonogenic survival","pmids":["32859985"],"confidence":"Medium","gaps":["Direct vs indirect interactions with Ku/DNA-PKcs/MCM not dissected","Single lab"]},{"year":2022,"claim":"Trapped XRN2 loading sites with a catalytic-dead mutant, pinpointing handoff ~2–20 nt downstream of CPSF73 (and RNase Z) cleavage and revealing pervasive promoter-proximal premature termination by the torpedo.","evidence":"5'-PO4 nascent RNA mapping with Xrn2 D235A, eNET-seq, ChIP and PRO-seq","pmids":["36396340"],"confidence":"High","gaps":["Structural basis of the physical handoff not resolved","How XRN2 distinguishes sense vs antisense promoter substrates unclear"]},{"year":2022,"claim":"Showed conformational dynamics around the XRN2 catalytic center, modulated by substrate and Mg2+, are intrinsic to catalysis—linking enzyme flexibility to activity.","evidence":"19F and methyl-TROSY NMR with in vitro degradation assays and mutagenesis","pmids":["36008487"],"confidence":"High","gaps":["Dynamics studied in isolation, not in the termination complex","Coupling of dynamics to phospho-regulation not examined"]},{"year":2022,"claim":"Defined a role for XRN2 in alternative polyadenylation, recruiting Sam68 to compete with CPSF and promote proximal poly(A) site usage and 3' UTR shortening.","evidence":"Co-IP, RIP, CLIP-seq, KD and poly(A)-seq","pmids":["36344846"],"confidence":"Medium","gaps":["Mechanism of CPSF competition not structurally defined","Single lab"]},{"year":2022,"claim":"Identified CAPRIN1 as a factor that recruits nuclear XRN2 into RNA granules to degrade developmental transcripts during ESC differentiation, extending XRN2 substrate targeting to development.","evidence":"CAPRIN1 knockout, RIP-seq, SLAM-seq, Co-IP interactome and IF co-localization","pmids":["36495875"],"confidence":"Medium","gaps":["Whether targeting is catalytic torpedo-like or processive decay unclear","Single lab"]},{"year":2023,"claim":"Added a ubiquitin-dependent recruitment layer—RNF8 ubiquitylates XRN2 to drive its occupancy at R-loop-prone loci, with loss promoting transcription-replication collisions in BRCA1-mutant cells.","evidence":"Co-IP, ubiquitylation assays, ChIP, DRIP and a mouse mammary tumor model","pmids":["37697435"],"confidence":"Medium","gaps":["Ubiquitylated residues and chain type not defined","Single lab"]},{"year":2024,"claim":"Provided structural views of the conserved Rat1/Xrn2-Rai1-Rtt103 torpedo complex across species, revealing a conserved core with variable accessory interfaces.","evidence":"Cryo-EM and X-ray crystallography of S. cerevisiae and C. thermophilum complexes","pmids":["39657659"],"confidence":"Medium","gaps":["Limited functional mutagenesis validation","Human complex architecture not directly determined"]},{"year":2025,"claim":"Established that XRN2 mediates constitutive rapid decay of hypomodified tRNAs—m7G-deficient tRNAs (METTL1 loss) and m1A-deficient tRNA-iMet (TRMT6/61A loss)—as a conserved tRNA surveillance pathway.","evidence":"siRNA/conditional depletion with time-resolved tRNA decay kinetics and Drosophila/human genetic epistasis (preprints)","pmids":["bio_10.1101_2025.11.05.686800","42239164"],"confidence":"Medium","gaps":["Preprint status, single labs","How XRN2 senses hypomodification not defined"]},{"year":2025,"claim":"Identified the HELQ helicase as a partner coordinating ATP-dependent R-loop unwinding with XRN2 RNA digestion, refining the molecular logic of R-loop resolution.","evidence":"Co-IP, in vitro helicase/exonuclease assays and cellular R-loop detection","pmids":["39965657"],"confidence":"Medium","gaps":["Single lab","Stoichiometry and order of helicase-exonuclease action not fully resolved"]},{"year":null,"claim":"How XRN2's many recruitment 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(PAXT-1/NKRF/CARF)"],"partners":["CPSF73","P54NRB/NONO","SENATAXIN/SETX","NKRF","CDKN2AIP/CARF","HNRNPK","CAPRIN1","RNF8"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q9H0D6","full_name":"5'-3' exoribonuclease 2","aliases":["DHM1-like protein","DHP protein"],"length_aa":950,"mass_kda":108.6,"function":"Possesses 5'->3' exoribonuclease activity (By similarity). 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RNA Regulation by XRN2 and XTBD Family Proteins.","date":"2021","source":"Cell structure and function","url":"https://pubmed.ncbi.nlm.nih.gov/34483148","citation_count":2,"is_preprint":false},{"pmid":"39965657","id":"PMC_39965657","title":"The human HELQ helicase and XRN2 exoribonuclease cooperate in R-loop resolution.","date":"2025","source":"Open biology","url":"https://pubmed.ncbi.nlm.nih.gov/39965657","citation_count":2,"is_preprint":false},{"pmid":"38339346","id":"PMC_38339346","title":"Molecular Basis of XRN2-Deficient Cancer Cell Sensitivity to Poly(ADP-ribose) Polymerase Inhibition.","date":"2024","source":"Cancers","url":"https://pubmed.ncbi.nlm.nih.gov/38339346","citation_count":2,"is_preprint":false},{"pmid":"39657659","id":"PMC_39657659","title":"Assembly of the Xrn2/Rat1-Rai1-Rtt103 termination complexes in mesophilic and thermophilic organisms.","date":"2024","source":"Structure (London, England : 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conditions","date":"2025-11-05","source":"bioRxiv","url":"https://doi.org/10.1101/2025.11.05.686800","citation_count":0,"is_preprint":true},{"pmid":null,"id":"bio_10.1101_2025.06.19.660564","title":"EXOSC10-mediated pre-tRNA surveillance safeguards neuron survival","date":"2025-06-19","source":"bioRxiv","url":"https://doi.org/10.1101/2025.06.19.660564","citation_count":0,"is_preprint":true}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":26415,"output_tokens":9517,"usd":0.111,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":19570,"output_tokens":7662,"usd":0.1447,"stage2_stop_reason":"end_turn"},"total_usd":0.2557,"stage1_batch_id":"msgbatch_01UT1AahFPCAyn2uVweS7A9z","stage2_batch_id":"msgbatch_01HuKWtKNT4Pqj1bc8eEP5RV","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2004,\n      \"finding\": \"XRN2 acts as a 5'→3' exonuclease 'torpedo' that degrades the downstream RNA product of co-transcriptional cleavage (CoTC) at the beta-globin gene, resulting in transcriptional termination by RNA Pol II. The CoTC autocatalytic RNA provides a free 5' end that XRN2 recognizes to degrade the nascent transcript and chase down Pol II.\",\n      \"method\": \"siRNA knockdown of XRN2, in vitro transcription/cleavage assays, nuclear run-on assays\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — functional KD with defined molecular readout, replicated in multiple subsequent studies across labs\",\n      \"pmids\": [\"15565158\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"XRN2 physically associates with p54nrb/PSF and 3'-processing factors, accumulates at the 3' end of transcribed genes, and is recruited to the 3'-processing machinery via p54nrb/PSF. In vitro, XRN2 degrades the downstream RNA after poly(A) site cleavage (but is not required for the cleavage itself), and degradation is stimulated when coupled to cleavage. p54nrb knockdown reduces XRN2 recruitment and causes termination defects.\",\n      \"method\": \"Co-immunoprecipitation, in vitro 3'-processing assays, ChIP, siRNA knockdown\",\n      \"journal\": \"Genes & development\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal interaction shown, in vitro activity assay, ChIP, and KD with functional readout in single lab with multiple orthogonal methods\",\n      \"pmids\": [\"17639083\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Senataxin resolves R-loop structures (RNA/DNA hybrids) that form behind elongating Pol II over G-rich pause sites downstream of poly(A) signals, and this resolution is required for XRN2 to access the 3' cleavage product and degrade it to promote Pol II termination.\",\n      \"method\": \"siRNA knockdown of senataxin and XRN2, R-loop immunofluorescence, nuclear run-on, ChIP\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — epistatic placement of senataxin upstream of XRN2, multiple orthogonal methods, replicated in subsequent studies\",\n      \"pmids\": [\"21700224\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"XRN2 plays a major role in mammalian pre-rRNA maturation (generating 5' ends of 5.8S and 28S rRNAs) and in degradation of aberrant/discarded pre-rRNA species via 5'→3' exonuclease activity. siRNA knockdown causes accumulation of precursors with 5' extensions.\",\n      \"method\": \"siRNA knockdown of Xrn2 in mouse cells, Northern blotting, primer extension analysis\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — clean KD with specific molecular readouts using multiple RNA analysis methods\",\n      \"pmids\": [\"21036871\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Decapping proteins Edc3, Dcp1a, and Dcp2 and the termination factor TTF2 co-immunoprecipitate with XRN2. Knockdown of decapping factors or XRN2/TTF2 redistributes Pol II away from the TSS toward upstream and downstream distal positions, indicating that coupled decapping of nascent transcripts and XRN2-mediated premature termination limits bidirectional Pol II elongation.\",\n      \"method\": \"Co-immunoprecipitation, ChIP-seq, siRNA knockdown\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal Co-IP plus genome-wide ChIP-seq with KD phenotype, multiple orthogonal methods in single lab\",\n      \"pmids\": [\"22483619\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Microprocessor (Drosha/Dgcr8) orchestrates recruitment of Setx and XRN2 to the HIV-1 promoter. Cleavage of the stem-loop RNA TAR initiates RNAPII pausing and premature termination at the HIV-1 promoter, with XRN2 acting cooperatively with Rrp6 downstream of microprocessor cleavage.\",\n      \"method\": \"ChIP-seq, siRNA knockdown, co-immunoprecipitation, transcriptional reporter assays\",\n      \"journal\": \"Cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genome-wide ChIP-seq combined with functional KD and mechanistic dissection of pathway order\",\n      \"pmids\": [\"22980978\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"XRN2 associates with nascent pre-mRNA and co-transcriptionally degrades aberrantly processed pre-mRNAs (e.g., splicing or 3'-processing mutants). XRN2 also degrades many endogenous pre-mRNAs when processing is inhibited by Spliceostatin A.\",\n      \"method\": \"ChIP, RNA immunoprecipitation, siRNA knockdown, RT-PCR, Northern blotting\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — ChIP and RIP with KD, but single lab\",\n      \"pmids\": [\"22522706\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"XRN2 uses a torpedo mechanism that operates genome-wide: a dominant-negative catalytically inactive Xrn2 mutant delayed termination at most poly(A) sites and some histone and snRNA genes. Kinetic competition between XRN2 exonuclease and Pol II elongation rate determines the location of termination—slow elongation shifts termination upstream and fast elongation extends it downstream.\",\n      \"method\": \"Dominant-negative XRN2 mutant expression, Pol II rate mutants, PRO-seq/GRO-seq genome-wide nascent RNA profiling\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genome-wide functional assay with mechanistic mutants, kinetic competition demonstrated, replicated conceptually across multiple labs\",\n      \"pmids\": [\"26474067\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"CDK9 (P-TEFb) phosphorylates XRN2 at Thr439 in vivo and in vitro. This phosphorylation enhances XRN2 enzymatic activity on synthetic substrates. Mutation of Thr439 to alanine (non-phosphorylatable) impairs XRN2 chromatin localization and increases readthrough transcription, phenocopying CDK9 inhibition.\",\n      \"method\": \"Chemical genetic substrate identification, in vitro kinase assay with purified proteins, phosphomimetic/phospho-null mutagenesis, ChIP, nascent RNA analysis\",\n      \"journal\": \"Genes & development\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro kinase assay plus mutagenesis plus in vivo functional validation in single lab with multiple orthogonal methods\",\n      \"pmids\": [\"26728557\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"XRN2 undergoes DNA damage-inducible nuclear re-localization, co-localizing with 53BP1 and R-loops in a transcription- and R-loop-dependent process. XRN2 loss leads to increased R-loops, genomic instability, replication stress, DSBs, and hypersensitivity to DNA damaging agents. DSBs from XRN2 loss occur at transcriptional pause sites, and XRN2-deficient cells show an R-loop- and transcription-dependent delay in DSB repair after ionizing radiation.\",\n      \"method\": \"Immunofluorescence, co-localization microscopy, R-loop detection (S9.6 antibody), siRNA knockdown, comet assay, gamma-H2AX staining, clonogenic survival assays\",\n      \"journal\": \"PLoS genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple readouts in single lab but primarily KD/localization-based without in vitro reconstitution\",\n      \"pmids\": [\"27437695\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Conditional depletion of XRN2 via gene editing reveals a clear general role in cotranscriptional degradation of 3'-flanking region RNA and transcriptional termination genome-wide. XRN2's effect on termination requires prior RNA cleavage by CPSF73. XRN2 plays no significant role in histone or snRNA gene termination. CPSF73 loss causes more extensive readthrough than XRN2 loss, indicating CPSF73 has a more foundational role.\",\n      \"method\": \"Auxin-inducible degron conditional depletion, mNET-seq genome-wide, catalytically inactive CPSF73 complementation\",\n      \"journal\": \"Genes & development\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — conditional depletion with genome-wide high-resolution nascent RNA mapping plus mutant complementation, rigorous epistasis\",\n      \"pmids\": [\"29432121\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"XRN2 protects HCV RNA from degradation in the cytoplasm is counteracted by miR-122: Xrn2 depletion increases HCV RNA accumulation, while overexpression diminishes it by affecting viral RNA stability (not translation or replication). During miR-122 sequestration, Xrn2 depletion restored HCV RNA abundance.\",\n      \"method\": \"siRNA knockdown, overexpression, luciferase reporter assays, RNA stability measurements\",\n      \"journal\": \"Cell host & microbe\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple complementary experiments (KD, OE, epistasis with miR-122), single lab\",\n      \"pmids\": [\"25121753\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"NKRF (NF-κB repressing factor) forms a pre-ribosomal subcomplex with DHX15 and XRN2, binds transcribed spacer regions of pre-rRNA (shown by CRAC), recruits XRN2 to nucleolar pre-ribosomal complexes, and is required for an early pre-rRNA cleavage step (A'). Depletion of NKRF or XRN2 impairs A' cleavage and causes accumulation of excised pre-rRNA spacer fragments.\",\n      \"method\": \"Co-immunoprecipitation, UV crosslinking and cDNA analysis (CRAC), siRNA knockdown, Northern blotting, sucrose gradient sedimentation\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal Co-IP, direct RNA crosslinking, KD with specific processing readouts, multiple orthogonal methods\",\n      \"pmids\": [\"28115624\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"In C. elegans, PAXT-1 (R05D11.6) stabilizes XRN2 protein levels and is required for miRNA turnover activity. A truncated PAXT-1 retaining only the DUF3469/XTBD domain suffices to restore viability, elevate XRN2 levels, and bind XRN2. Human CDKN2AIP/CARF and NKRF interact with XRN2 through this same XTBD domain.\",\n      \"method\": \"TALEN-mediated genome editing, co-immunoprecipitation, western blotting, worm survival assays, in vivo complementation\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genome editing KO, direct binding shown, domain sufficiency demonstrated in vivo, conservation tested in human proteins\",\n      \"pmids\": [\"24462208\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"The XTBD (XRN2-binding domain) from PAXT-1 stably interconnects two XRN2 domains through numerous interacting residues (crystal structure). Mutation of a single critical residue disrupts XTBD-XRN2 complexes in vitro and recapitulates paxt-1-null phenotypes in vivo. Vertebrate XTBD-containing proteins (CDKN2AIPNL) bind XRN2 in vitro and can substitute for PAXT-1 in C. elegans. In the absence of substrate, complex formation with PAXT-1 serves to preserve XRN2 stability.\",\n      \"method\": \"X-ray crystallography, in vitro binding assays, site-directed mutagenesis, C. elegans genetic complementation\",\n      \"journal\": \"Nature structural & molecular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — crystal structure plus mutagenesis plus in vivo functional validation with single critical residue identified\",\n      \"pmids\": [\"26779609\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"In Tetrahymena, the Piwi protein Twi12 binds mature 3' tRNA fragments and assembles a complex with nuclear exonuclease Xrn2. Twi12 stabilizes and localizes Xrn2 to the nucleus, and stimulates its exonuclease activity. Loss of Twi12 or Xrn2 causes rRNA processing defects. Twi12 sRNA binding is required for nuclear import of the complex.\",\n      \"method\": \"Co-immunoprecipitation, sRNA sequencing, ribosome profiling, northern blotting, localization studies, Xrn2 activity assays\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct complex assembly shown, functional stimulation demonstrated, nuclear import requirement shown, multiple orthogonal methods\",\n      \"pmids\": [\"23084833\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"CARF (collaborator of ARF) directly associates with XRN2 and regulates its subcellular distribution: CARF overexpression increases XRN2 in the nucleoplasm and suppresses pre-rRNA processing, causing accumulation of 5'-extended 45S/47S pre-rRNA; CARF knockdown increases XRN2 in the nucleolar fraction. This phenocopies XRN2 knockdown in the nucleolus.\",\n      \"method\": \"Co-immunoprecipitation, cell fractionation, immunocytochemistry, western blotting, northern blotting, siRNA knockdown/overexpression\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct interaction, localization shift, and rRNA processing phenotype shown, but single lab\",\n      \"pmids\": [\"26531822\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"hnRNPK co-immunoprecipitates with XRN2 in nuclear extracts; hnRNPK knockdown decreases XRN2 recruitment along EGR1 and downstream of its poly(A) signal (ChIP-seq), and increases pre-RNA read-through downstream of the EGR1 polyadenylation site, suggesting hnRNPK recruits XRN2 to gene loci to regulate termination.\",\n      \"method\": \"ChIP-seq, siRNA knockdown, co-immunoprecipitation with mass spectrometry, RT-PCR\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — ChIP-seq plus Co-IP and KD functional readout, single lab\",\n      \"pmids\": [\"23857582\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Rapid depletion of XRN2 (using degron technology) reveals that XRN2 loss uncovers different mechanisms for early termination of transcription from protein-coding gene promoters, and that XRN2 has little activity on exosome (DIS3/EXOSC10) substrates.\",\n      \"method\": \"Auxin-inducible degron rapid protein depletion, RNA-seq, PRO-seq\",\n      \"journal\": \"Cell reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — rapid conditional depletion with genome-wide readout, single lab\",\n      \"pmids\": [\"30840897\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"XRN2 is recruited to preinitiation complexes and travels to 3' gene ends. Mapping of 5'-PO4 ends using catalytically inactive Xrn2(D235A) shows XRN2 loading sites ~2–20 bases downstream of CPSF73 cleavage at polyA sites and histone 3' ends, indicating handoff from CPSF73 to XRN2. A similar handoff occurs at tRNA 3' ends after RNase Z cleavage. XRN2 also degrades sense and antisense nascent RNA within a few bases of the TSS, revealing widespread promoter-proximal premature termination by the torpedo mechanism.\",\n      \"method\": \"5'-PO4 nascent RNA mapping with active-site mutant (Xrn2 D235A), eNET-seq, ChIP, PRO-seq\",\n      \"journal\": \"Genes & development\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — active-site mutant substrate trapping with genome-wide nascent RNA mapping, rigorous mechanistic design\",\n      \"pmids\": [\"36396340\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"NMR studies reveal that Xrn2 is highly dynamic around its catalytic center in the apo state, and substrate plus magnesium shifts the conformational equilibrium toward an active state. A mutation that attenuates these dynamics also reduces catalytic activity, establishing that conformational dynamics are integral to the catalytic mechanism.\",\n      \"method\": \"Fluorine and methyl-TROSY NMR spectroscopy, in vitro RNA degradation assays, mutagenesis\",\n      \"journal\": \"Nature chemical biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — NMR structure/dynamics plus mutagenesis plus in vitro activity assay, orthogonal methods in single rigorous study\",\n      \"pmids\": [\"36008487\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"RNF8 ubiquitylates XRN2, facilitating its recruitment to R-loop-prone genomic loci. RNF8 deficiency decreases XRN2 occupancy at R-loop-prone sites, promoting R-loop accumulation and transcription-replication collisions, leading to genomic instability in BRCA1-mutant cells.\",\n      \"method\": \"Co-immunoprecipitation, ubiquitylation assays, ChIP, R-loop detection (DRIP), genome stability assays, mouse mammary tumorigenesis model\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — ubiquitylation demonstrated, ChIP showing reduced recruitment, functional consequence shown, single lab\",\n      \"pmids\": [\"37697435\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"XRN2-mediated R-loop resolution is required for Ku70 binding to DNA ends and initiation of NHEJ repair. XRN2 loss also decreases homologous recombination repair, but this is not restored by RNaseH1 overexpression, indicating that unregulated transcription (not just R-loops) inhibits HR.\",\n      \"method\": \"siRNA knockdown, RNaseH1 overexpression, Ku70 ChIP, DR-GFP and EJ5-GFP HR/NHEJ reporter assays\",\n      \"journal\": \"Cancers\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — epistasis with RNaseH1 plus DSB repair reporter assays, mechanistic dissection in single lab\",\n      \"pmids\": [\"32645903\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Genome-wide DRIP-seq reveals that XRN2 depletion causes hundreds to thousands of R-loop gains preferentially at highly transcribed genes at transcription termination sites. XRN2, DDX5, and PRMT5 share many R-loop gain loci at termination sites, but DDX5 has unique R-loop gain peaks near TSS not overlapping siXRN2, indicating distinct roles.\",\n      \"method\": \"DRIP-seq (genome-wide R-loop mapping), siRNA knockdown\",\n      \"journal\": \"Life science alliance\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genome-wide direct R-loop mapping with KD, single lab\",\n      \"pmids\": [\"32747416\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"In fission yeast, Dhp1/Xrn2 cooperates with RNA elimination factors to promote premature termination at meiotic genes and facilitate facultative heterochromatin formation. Dhp1 also interacts with the Clr4/Suv39h methyltransferase complex and acts directly to nucleate heterochromatin.\",\n      \"method\": \"Genetic epistasis, ChIP, co-immunoprecipitation, reporter gene silencing assays in S. pombe\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic epistasis plus biochemical interaction plus silencing assays, fission yeast ortholog\",\n      \"pmids\": [\"26631744\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"XRN2 promotes recruitment of Sam68 to target transcripts, where the Sam68/XRN2 complex competes with CPSF for binding to strong distal polyadenylation signals, thereby promoting usage of suboptimal proximal polyadenylation signals and 3' UTR shortening.\",\n      \"method\": \"Co-immunoprecipitation, RNA immunoprecipitation, CLIP-seq, siRNA knockdown, poly(A)-seq transcriptome profiling\",\n      \"journal\": \"Nature structural & molecular biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal Co-IP, CLIP-seq, and transcriptome-wide APA profiling with KD, single lab\",\n      \"pmids\": [\"36344846\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"In C. elegans, Nkx2-5 deficiency affects Xrn2 binding to target loci and results in increased RNAPII occupancy and expression of mRNAs with long 3' UTRs from heart development genes. Genetic interaction (double heterozygous Nkx2-5+/−; Xrn2+/−) causes ventricular septum defects not seen in single heterozygotes, establishing that Nkx2-5 and Xrn2 cooperate in regulating alternative polyadenylation during heart development.\",\n      \"method\": \"ChIP, siRNA knockdown, genetic compound heterozygotes in mice, 3'-seq for APA analysis\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic epistasis in vivo plus ChIP showing XRN2 mis-recruitment, single lab\",\n      \"pmids\": [\"27331609\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"In C. elegans, XRN2 loss of function (null or catalytic-dead) causes molting defect and larval arrest, demonstrating that XRN2 catalytic activity is essential for development. XRN2 has specificity for a subset of miRNAs in vivo—some rapidly decaying miRNAs are stabilized by XRN2 loss while others continue to decay, indicating XRN2-independent decay pathways for certain miRNAs.\",\n      \"method\": \"Conditional allele engineering (temperature-sensitive), null mutation, small RNA sequencing, miRNA stability assays\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — conditional allele with specific molecular readout for miRNA substrates, single lab\",\n      \"pmids\": [\"24445807\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Nuclear XRN2 degrades the 3' fragments of pre-mRNA generated by RNase H1-mediated cleavage of ASO-targeted transcripts from their 5' ends, while XRN1 is responsible for cytoplasmic mRNA fragment degradation after siRNA-mediated cleavage.\",\n      \"method\": \"siRNA knockdown of XRN1 and XRN2, northern blotting for cleavage fragment detection, nuclear/cytoplasmic fractionation\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — KD with specific fragment detection, single lab, single method set\",\n      \"pmids\": [\"26159921\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"NPGPx covalently binds to XRN2 upon non-targeting siRNA stress and facilitates XRN2-mediated removal of accumulated non-targeting siRNA, relieving cellular stress.\",\n      \"method\": \"Co-immunoprecipitation, covalent crosslinking assay, siRNA accumulation measurement, cell growth assays\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single Co-IP/covalent interaction claim, single lab, limited mechanistic follow-up\",\n      \"pmids\": [\"21908404\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"CAPRIN1 promotes degradation of developmental transcripts during early ESC differentiation via XRN2. Upon differentiation, XRN2 localizes to the nucleus and co-localizes with CAPRIN1 in small RNA granules in a CAPRIN1-dependent manner, identifying CAPRIN1 as a factor that recruits XRN2 to specific RNA targets.\",\n      \"method\": \"CAPRIN1 knockout, RIP-seq, SLAM-seq, XRN2 co-immunoprecipitation/interactome, immunofluorescence co-localization\",\n      \"journal\": \"Developmental cell\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — RIP-seq plus SLAM-seq kinetics plus Co-IP interactome and localization, single lab\",\n      \"pmids\": [\"36495875\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"XRN2 interacts with DNA repair/replication proteins including Ku70-Ku80, DNA-PKcs, PARP1, and MCM2-7 as shown by tandem affinity purification-mass spectrometry. XRN2 depletion hyperactivates PARP1 activity, and combined XRN2 depletion and PARP1 inhibition results in synthetic lethality.\",\n      \"method\": \"Tandem affinity purification-mass spectrometry (TAP-MS), Co-IP, PARP1 activity assay, siRNA knockdown, clonogenic survival, flow cytometry\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — TAP-MS interactome plus functional synthetic lethality validation, single lab\",\n      \"pmids\": [\"32859985\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"XRN2 regulates TERRA RNA stability; XRN2 depletion in ALT-positive cancer cells increases TERRA R-loops and exacerbates ALT activity, establishing XRN2 as a key determinant of TERRA metabolism at telomeres.\",\n      \"method\": \"siRNA knockdown, northern blotting for TERRA, DRIP-qPCR for R-loops, ALT-associated PML body foci quantification\",\n      \"journal\": \"FEBS letters\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single KD with functional readout, limited mechanistic detail, single lab\",\n      \"pmids\": [\"37191774\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Structural characterization of the Xrn2/Rat1-Rai1-Rtt103 torpedo termination complex from S. cerevisiae and C. thermophilum reveals conserved protein core folds but variable interaction interfaces: in the mesophile, Rtt103 uses an unstructured region to augment a Rai1 β-sheet, while in the thermophile Rtt103 binds a C-terminal Rai1 helix via a CTD-interacting domain with α-helical fold.\",\n      \"method\": \"Cryo-EM, X-ray crystallography, structural biology\",\n      \"journal\": \"Structure\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Weak — structural determination but limited functional mutagenesis validation reported in abstract, single study\",\n      \"pmids\": [\"39657659\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Full-length NKRF contains an N-terminal XTBD (XRN2-binding domain) encoded from an alternative upstream AUG start codon; this XTBD is essential for XRN2 retention in the nucleolus. NKRF is tethered in the nucleolus by binding rRNA and controls spatial distribution of XRN2 between nucleoplasm and nucleolus to regulate early pre-rRNA processing.\",\n      \"method\": \"Alternative start codon identification, co-immunoprecipitation, immunofluorescence, subcellular fractionation, domain deletion mutagenesis\",\n      \"journal\": \"The Biochemical journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — novel XTBD domain identified and functionally validated with localization and interaction data, single lab\",\n      \"pmids\": [\"32011671\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"HELQ helicase interacts with XRN2 and cooperates with it in R-loop resolution: HELQ unwinds R-loops (requires ATPase activity) and is functionally coordinated with XRN2-mediated RNA digestion, shown both in cells and in vitro.\",\n      \"method\": \"Co-immunoprecipitation, in vitro helicase and exonuclease assays, R-loop detection in cells, siRNA/inhibitor experiments\",\n      \"journal\": \"Open biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vitro functional assay plus cell-based interaction and R-loop resolution, single lab\",\n      \"pmids\": [\"39965657\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"XRN2 degrades hypomethylated (m1A-lacking) tRNA-iMet in human cells: acute loss of TRMT6/61A leads to rapid XRN2-dependent degradation of tRNA-iMet, reducing global protein synthesis. XRN2 inhibition rescues tRNA-iMet levels and reverses growth defects in TRMT6/61A-depleted cells.\",\n      \"method\": \"dTAG rapid depletion system, tRNA-seq, pulse-chase tRNA stability measurements, XRN2 knockdown/inhibition complementation assays\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — conditional depletion with kinetic measurements and rescue validation, but preprint and single lab\",\n      \"pmids\": [\"42239164\"],\n      \"is_preprint\": true\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"XRN2 mediates accelerated decay of m7G-hypomodified tRNAs under physiological (non-stress) conditions: XRN2 knockdown restores tRNA levels diminished by METTL1 depletion. Partial loss of Drosophila XRN2 ortholog Rat1 genetically rescues male sterility of mettl1 mutants, establishing a conserved constitutive rapid tRNA decay pathway.\",\n      \"method\": \"siRNA knockdown of XRN2, conditional protein knockdown with time-resolved tRNA decay kinetics, Drosophila genetic epistasis\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — conditional depletion with kinetic decay measurements plus in vivo genetic epistasis across species, but preprint\",\n      \"pmids\": [\"bio_10.1101_2025.11.05.686800\"],\n      \"is_preprint\": true\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"XRN2 accelerates maturation of pre-miR-10a by binding to the precursor miRNA in a DICER-independent manner, promoting its maturation and thereby inducing EMT and metastasis in lung cancer.\",\n      \"method\": \"Co-immunoprecipitation/pulldown of XRN2 with pre-miR-10a, in vitro processing assays, overexpression and knockdown, in vivo metastasis assays\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single pulldown and processing assay, unusual proposed mechanism (XRN2 as miRNA maturation factor rather than degradase), single lab without independent replication\",\n      \"pmids\": [\"28319071\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"XRN2 is a nuclear 5'→3' exoribonuclease that promotes RNA Pol II transcription termination genome-wide via the 'torpedo' mechanism—loading onto 5'-phosphate RNA ends generated by CPSF73 cleavage at poly(A) sites and degrading the remaining nascent transcript to chase down elongating Pol II—a process regulated by CDK9-mediated phosphorylation at Thr439 and facilitated by cofactors including p54nrb/PSF, senataxin (which resolves inhibitory R-loops), and XTBD-domain proteins (PAXT-1/NKRF/CARF) that stabilize and localize XRN2; it also processes pre-rRNA (5.8S and 28S maturation), degrades aberrant pre-mRNAs co-transcriptionally, turns over specific miRNAs and tRNAs, resolves R-loops to prevent genomic instability and enable DSB repair, and regulates alternative polyadenylation.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"XRN2 is a nuclear 5'→3' exoribonuclease that enforces RNA polymerase II transcription termination genome-wide through the 'torpedo' mechanism: it loads onto the 5'-phosphate RNA end generated by CPSF73 cleavage at poly(A) sites and degrades the downstream nascent transcript to chase down and evict elongating Pol II [#0, #10, #19]. Mapping of XRN2 loading sites with a catalytically inactive mutant places handoff a few bases downstream of CPSF73 cleavage at poly(A) and histone 3' ends, and an analogous handoff occurs at tRNA 3' ends after RNase Z cleavage [#19]; XRN2 also degrades sense and antisense transcripts near the TSS to effect widespread promoter-proximal premature termination [#19, #4]. The position of termination is set by kinetic competition between XRN2 exonuclease progression and Pol II elongation rate [#7], and access to the cleaved product requires resolution of R-loops over G-rich pause sites by senataxin [#2]. XRN2 catalytic activity and chromatin loading are enhanced by CDK9/P-TEFb phosphorylation at Thr439 [#8], its recruitment to gene 3' ends is mediated by interacting factors including p54nrb/PSF and hnRNPK [#1, #17], and conformational dynamics around its catalytic center are intrinsic to its degradation activity [#20]. Beyond termination, XRN2 carries out pre-rRNA maturation—generating 5' ends of 5.8S and 28S rRNA and executing an early A' cleavage step within an NKRF/DHX15 pre-ribosomal subcomplex [#3, #12]. XRN2 protein stability and nucleoplasm/nucleolus partitioning are controlled by XTBD-domain proteins (PAXT-1, NKRF, CARF/CDKN2AIP), which dock onto and bridge two XRN2 domains [#13, #14, #16, #34]. XRN2 additionally degrades aberrantly processed nascent pre-mRNAs co-transcriptionally [#6], turns over specific miRNAs and hypomodified tRNAs [#27, #37], resolves R-loops to suppress genomic instability and enable DSB repair [#9, #22], and shapes alternative polyadenylation [#25].\",\n  \"teleology\": [\n    {\n      \"year\": 2004,\n      \"claim\": \"Established the foundational 'torpedo' model—that a 5'→3' exonuclease degrades the downstream cleavage product to terminate Pol II transcription—answering how termination is mechanistically coupled to nascent RNA cleavage.\",\n      \"evidence\": \"siRNA knockdown of XRN2 with in vitro cleavage and nuclear run-on assays at the beta-globin gene\",\n      \"pmids\": [\"15565158\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Demonstrated at a single gene rather than genome-wide\", \"Did not define how XRN2 is recruited to the 3'-processing site\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Identified how XRN2 is physically delivered to gene 3' ends, linking it to the cleavage/polyadenylation machinery via p54nrb/PSF.\",\n      \"evidence\": \"Co-IP, in vitro 3'-processing assays, ChIP and siRNA knockdown\",\n      \"pmids\": [\"17639083\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"XRN2 not required for the cleavage step itself\", \"Recruitment mechanism beyond p54nrb/PSF unresolved\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Extended XRN2 function beyond termination to ribosome biogenesis, showing it generates mature rRNA 5' ends and clears aberrant pre-rRNA.\",\n      \"evidence\": \"siRNA knockdown in mouse cells with Northern blotting and primer extension\",\n      \"pmids\": [\"21036871\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not identify the nucleolar recruitment factors\", \"Relationship to termination role not addressed\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Defined a prerequisite for torpedo termination—senataxin must resolve R-loops behind paused Pol II so XRN2 can access the cleavage product.\",\n      \"evidence\": \"siRNA knockdown of senataxin and XRN2 with R-loop IF, nuclear run-on and ChIP\",\n      \"pmids\": [\"21700224\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In vitro reconstitution of the senataxin–XRN2 handoff not shown\", \"Generality across genes not established at this stage\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Showed XRN2 termination is not restricted to gene 3' ends but limits bidirectional/promoter-proximal Pol II elongation through coupling to decapping and TTF2, and operates at the HIV-1 promoter downstream of Microprocessor cleavage.\",\n      \"evidence\": \"Co-IP, ChIP-seq and siRNA knockdown (decapping factors/TTF2; Drosha/DGCR8/Setx)\",\n      \"pmids\": [\"22483619\", \"22980978\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct vs indirect interactions with decapping factors not fully resolved\", \"Substrate 5' end chemistry at promoters not mapped\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Demonstrated XRN2 surveys nascent pre-mRNA and co-transcriptionally degrades transcripts that fail splicing or 3'-processing, broadening its role to RNA quality control.\",\n      \"evidence\": \"ChIP, RIP, siRNA knockdown, RT-PCR and Northern blotting with Spliceostatin A\",\n      \"pmids\": [\"22522706\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single lab\", \"Recognition of aberrant transcripts mechanistically undefined\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Identified the XTBD-domain protein family (PAXT-1 and human CARF/NKRF homologs) as conserved factors that bind XRN2 and stabilize the protein, defining a post-translational control layer.\",\n      \"evidence\": \"TALEN editing, Co-IP, complementation and survival assays in C. elegans\",\n      \"pmids\": [\"24462208\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of XTBD–XRN2 binding not yet resolved\", \"Whether stabilization affects substrate selection unclear\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Showed XRN2 turns over specific RNA substrates in trans—nuclear ASO/RNase H1-generated pre-mRNA 3' fragments—distinguishing its nuclear role from cytoplasmic XRN1.\",\n      \"evidence\": \"siRNA knockdown of XRN1/XRN2 with fragment Northern blotting and fractionation\",\n      \"pmids\": [\"26159921\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single method set\", \"Endogenous physiological substrates of this activity not defined\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Demonstrated that XTBD protein CARF controls XRN2 nucleoplasm/nucleolus partitioning and thereby tunes pre-rRNA processing.\",\n      \"evidence\": \"Co-IP, cell fractionation, immunocytochemistry and KD/overexpression with Northern blotting\",\n      \"pmids\": [\"26531822\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single lab\", \"Signal triggering CARF-dependent relocalization unknown\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Established a torpedo-independent function—nuclear stabilization of cytoplasmic HCV RNA antagonized by miR-122—indicating XRN2 substrate effects can be both degradative and protective in viral RNA metabolism.\",\n      \"evidence\": \"siRNA knockdown, overexpression, luciferase reporters and RNA stability assays\",\n      \"pmids\": [\"25121753\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism of XRN2-mediated protection vs degradation unclear\", \"Single lab\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Proved the torpedo operates genome-wide and that termination position is governed by kinetic competition between XRN2 and Pol II elongation rate.\",\n      \"evidence\": \"Dominant-negative catalytic-dead XRN2 with Pol II rate mutants and PRO-seq/GRO-seq\",\n      \"pmids\": [\"26474067\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Exact handoff coordinates from CPSF73 not yet mapped\", \"Why histone/snRNA genes show partial dependence unresolved\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Identified CDK9/P-TEFb phosphorylation of XRN2 at Thr439 as a regulatory switch enhancing activity and chromatin loading, linking elongation control kinases to termination.\",\n      \"evidence\": \"Chemical-genetic substrate ID, in vitro kinase assay, phospho-mutant mutagenesis, ChIP and nascent RNA analysis\",\n      \"pmids\": [\"26728557\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether phosphorylation alters substrate affinity vs catalysis not dissected\", \"Additional regulatory phosphosites unexplored\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Provided the structural basis for XTBD-mediated XRN2 stabilization, showing the domain bridges two XRN2 lobes and that a single residue mutation abolishes the complex and phenocopies the null.\",\n      \"evidence\": \"X-ray crystallography, in vitro binding, mutagenesis and C. elegans complementation\",\n      \"pmids\": [\"26779609\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not resolve full-length XRN2 catalytic architecture\", \"Functional consequence of stabilization on individual substrates not mapped\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Linked XRN2 to genome maintenance—its loss elevates R-loops, drives DSBs at transcriptional pause sites, and delays DSB repair, integrating its RNA-processing role with DNA stability.\",\n      \"evidence\": \"IF/co-localization with 53BP1, S9.6 R-loop detection, comet/γH2AX assays and clonogenic survival\",\n      \"pmids\": [\"27437695\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No in vitro reconstitution of R-loop resolution by XRN2\", \"Direct vs indirect contribution to repair unresolved\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Assembled XRN2 into an NKRF/DHX15 pre-ribosomal subcomplex that binds pre-rRNA spacers and executes the early A' cleavage step, mechanistically grounding the rRNA processing role.\",\n      \"evidence\": \"Co-IP, CRAC, siRNA knockdown, Northern blotting and sucrose gradients\",\n      \"pmids\": [\"28115624\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Catalytic basis of A' cleavage by XRN2 vs accessory factors unclear\", \"Coordination with DHX15 helicase activity undefined\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Used rapid conditional depletion and CPSF73 epistasis to establish that genome-wide XRN2-dependent termination strictly requires prior CPSF73 cleavage, while CPSF73 has a more foundational role and XRN2 is dispensable at histone/snRNA genes.\",\n      \"evidence\": \"Auxin-inducible degron depletion, mNET-seq and catalytic-inactive CPSF73 complementation\",\n      \"pmids\": [\"29432121\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"What terminates histone/snRNA genes independently of XRN2 unresolved\", \"Residual readthrough mechanisms not defined\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Distinguished XRN2-dependent early termination from exosome activity, showing XRN2 has little role on DIS3/EXOSC10 substrates.\",\n      \"evidence\": \"Auxin-inducible degron rapid depletion with RNA-seq and PRO-seq\",\n      \"pmids\": [\"30840897\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single lab\", \"Partition of substrates between torpedo and exosome incompletely mapped\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Mapped XRN2 R-loop substrates genome-wide and showed its loss causes R-loop gains preferentially at termination sites of highly transcribed genes, distinguishing it from DDX5/PRMT5.\",\n      \"evidence\": \"DRIP-seq with siRNA knockdown\",\n      \"pmids\": [\"32747416\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single lab\", \"Whether R-loop resolution is degradative or via partner helicases not established\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Connected XRN2 R-loop resolution to DSB repair pathway choice, showing it is required for Ku70 loading and NHEJ initiation and supports HR independently of R-loops.\",\n      \"evidence\": \"siRNA knockdown, RNaseH1 overexpression, Ku70 ChIP and DR-GFP/EJ5-GFP reporters\",\n      \"pmids\": [\"32645903\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct physical contribution of XRN2 to repair complexes unclear\", \"Single lab\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Defined an XRN2 interactome with DNA repair/replication machinery and revealed a synthetic-lethal relationship with PARP1 inhibition, suggesting therapeutic context.\",\n      \"evidence\": \"TAP-MS, Co-IP, PARP1 activity assay, KD with clonogenic survival\",\n      \"pmids\": [\"32859985\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct vs indirect interactions with Ku/DNA-PKcs/MCM not dissected\", \"Single lab\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Trapped XRN2 loading sites with a catalytic-dead mutant, pinpointing handoff ~2–20 nt downstream of CPSF73 (and RNase Z) cleavage and revealing pervasive promoter-proximal premature termination by the torpedo.\",\n      \"evidence\": \"5'-PO4 nascent RNA mapping with Xrn2 D235A, eNET-seq, ChIP and PRO-seq\",\n      \"pmids\": [\"36396340\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of the physical handoff not resolved\", \"How XRN2 distinguishes sense vs antisense promoter substrates unclear\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Showed conformational dynamics around the XRN2 catalytic center, modulated by substrate and Mg2+, are intrinsic to catalysis—linking enzyme flexibility to activity.\",\n      \"evidence\": \"19F and methyl-TROSY NMR with in vitro degradation assays and mutagenesis\",\n      \"pmids\": [\"36008487\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Dynamics studied in isolation, not in the termination complex\", \"Coupling of dynamics to phospho-regulation not examined\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Defined a role for XRN2 in alternative polyadenylation, recruiting Sam68 to compete with CPSF and promote proximal poly(A) site usage and 3' UTR shortening.\",\n      \"evidence\": \"Co-IP, RIP, CLIP-seq, KD and poly(A)-seq\",\n      \"pmids\": [\"36344846\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism of CPSF competition not structurally defined\", \"Single lab\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Identified CAPRIN1 as a factor that recruits nuclear XRN2 into RNA granules to degrade developmental transcripts during ESC differentiation, extending XRN2 substrate targeting to development.\",\n      \"evidence\": \"CAPRIN1 knockout, RIP-seq, SLAM-seq, Co-IP interactome and IF co-localization\",\n      \"pmids\": [\"36495875\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether targeting is catalytic torpedo-like or processive decay unclear\", \"Single lab\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Added a ubiquitin-dependent recruitment layer—RNF8 ubiquitylates XRN2 to drive its occupancy at R-loop-prone loci, with loss promoting transcription-replication collisions in BRCA1-mutant cells.\",\n      \"evidence\": \"Co-IP, ubiquitylation assays, ChIP, DRIP and a mouse mammary tumor model\",\n      \"pmids\": [\"37697435\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Ubiquitylated residues and chain type not defined\", \"Single lab\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Provided structural views of the conserved Rat1/Xrn2-Rai1-Rtt103 torpedo complex across species, revealing a conserved core with variable accessory interfaces.\",\n      \"evidence\": \"Cryo-EM and X-ray crystallography of S. cerevisiae and C. thermophilum complexes\",\n      \"pmids\": [\"39657659\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Limited functional mutagenesis validation\", \"Human complex architecture not directly determined\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Established that XRN2 mediates constitutive rapid decay of hypomodified tRNAs—m7G-deficient tRNAs (METTL1 loss) and m1A-deficient tRNA-iMet (TRMT6/61A loss)—as a conserved tRNA surveillance pathway.\",\n      \"evidence\": \"siRNA/conditional depletion with time-resolved tRNA decay kinetics and Drosophila/human genetic epistasis (preprints)\",\n      \"pmids\": [\"bio_10.1101_2025.11.05.686800\", \"42239164\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Preprint status, single labs\", \"How XRN2 senses hypomodification not defined\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Identified the HELQ helicase as a partner coordinating ATP-dependent R-loop unwinding with XRN2 RNA digestion, refining the molecular logic of R-loop resolution.\",\n      \"evidence\": \"Co-IP, in vitro helicase/exonuclease assays and cellular R-loop detection\",\n      \"pmids\": [\"39965657\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single lab\", \"Stoichiometry and order of helicase-exonuclease action not fully resolved\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How XRN2's many recruitment factors (p54nrb/PSF, hnRNPK, CAPRIN1, NKRF, RNF8) and modifications (CDK9 phosphorylation, ubiquitylation) are integrated to select among its diverse substrate classes—termination, rRNA, tRNA, miRNA, R-loops, APA—remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No unified model linking partner choice to substrate specificity\", \"Structure of the human torpedo complex on a Pol II substrate not determined\", \"Whether catalysis vs scaffolding dominates each non-termination role is unclear\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140098\", \"supporting_discovery_ids\": [0, 3, 19, 20, 28]},\n      {\"term_id\": \"GO:0016787\", \"supporting_discovery_ids\": [0, 19, 20]},\n      {\"term_id\": \"GO:0003723\", \"supporting_discovery_ids\": [6, 12, 25]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [9, 28, 30]},\n      {\"term_id\": \"GO:0005730\", \"supporting_discovery_ids\": [3, 12, 16, 34]},\n      {\"term_id\": \"GO:0005654\", \"supporting_discovery_ids\": [16, 34]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-74160\", \"supporting_discovery_ids\": [0, 7, 10, 19]},\n      {\"term_id\": \"R-HSA-8953854\", \"supporting_discovery_ids\": [3, 12, 27, 37]},\n      {\"term_id\": \"R-HSA-73894\", \"supporting_discovery_ids\": [9, 22, 31]},\n      {\"term_id\": \"R-HSA-1852241\", \"supporting_discovery_ids\": [3, 12]}\n    ],\n    \"complexes\": [\n      \"Xrn2/Rat1-Rai1-Rtt103 torpedo complex\",\n      \"NKRF-DHX15-XRN2 pre-ribosomal subcomplex\",\n      \"XTBD-XRN2 stabilization complex (PAXT-1/NKRF/CARF)\"\n    ],\n    \"partners\": [\n      \"CPSF73\",\n      \"p54nrb/NONO\",\n      \"senataxin/SETX\",\n      \"NKRF\",\n      \"CDKN2AIP/CARF\",\n      \"hnRNPK\",\n      \"CAPRIN1\",\n      \"RNF8\"\n    ],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":7,"faith_total":7,"faith_pct":100.0}}