{"gene":"XRN1","run_date":"2026-06-11T09:02:06","timeline":{"discoveries":[{"year":1990,"finding":"XRN1 encodes a 5'→3' exoribonuclease in yeast; disruption of the gene is not lethal but markedly reduces cell growth rate, which is rescued by reintroduction of XRN1 on a plasmid.","method":"Gene disruption (knockout) in haploid yeast, complementation with plasmid-borne XRN1, poly(A) hydrolytic activity assay, immunoreactivity","journal":"Gene","confidence":"High","confidence_rationale":"Tier 2 / Strong — clean KO with defined phenotype, enzymatic activity confirmed, complementation rescue, replicated in subsequent work","pmids":["1979303"],"is_preprint":false},{"year":1992,"finding":"XRN1 (also known as DST2/SEP1/KEM1/RAR5) encodes a 160-kDa 5'→3' exoribonuclease; xrn1-deleted yeast cells show 2–4-fold longer half-lives of specific short-lived mRNAs, increased cellular protein levels, and reduced rRNA synthesis rate, demonstrating XRN1's key role in mRNA turnover.","method":"Gene sequencing, gene disruption, Northern analysis of specific mRNA half-lives, metabolic labeling, PAGE analysis","journal":"Gene","confidence":"High","confidence_rationale":"Tier 2 / Strong — direct measurement of mRNA half-lives in KO strain, multiple orthogonal methods, replicated across studies","pmids":["1398123"],"is_preprint":false},{"year":1991,"finding":"The SEP1 (XRN1) protein promotes homologous DNA pairing (strand exchange) in vitro and is required in meiosis; sep1 mutants show reduced meiotic recombination and defective sporulation, with arrest after commitment to recombination but before meiosis I.","method":"Gene cloning, protein overproduction and purification, in vitro strand exchange assay, mutant phenotype analysis (sporulation, recombination)","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro reconstitution of strand exchange activity plus genetic loss-of-function with defined meiotic phenotype","pmids":["1840632"],"is_preprint":false},{"year":1993,"finding":"XRN1/KEM1 encodes the major cytoplasmic 5'→3' exoribonuclease (p175); its essential nuclear paralog HKE1/RAT1 encodes a related 5'→3' exoribonuclease (p116); overexpression of XRN1 p175 cannot rescue loss of HKE1/RAT1, indicating non-redundant functions.","method":"Gene cloning, in vitro 5'→3' exoribonuclease activity assay, immunodepletion, complementation test","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro enzymatic activity demonstrated, immunoreactive RNase activity abolished with specific antiserum, complementation failure established non-redundancy","pmids":["8417335"],"is_preprint":false},{"year":1994,"finding":"Sep1 (XRN1) promotes paranemic joint formation between homologous DNA molecules in vitro; the pairing does not require net intertwining and requires as little as 41 bp of homology; the exonuclease activity of Sep1 is not responsible for the joint.","method":"Nitrocellulose filter binding assay, electron microscopy, in vitro DNA pairing with defined substrates, exonuclease activity controls","journal":"Genes & development","confidence":"High","confidence_rationale":"Tier 1 / Moderate — reconstituted in vitro pairing activity with multiple structural methods and controls ruling out exonuclease as mechanism","pmids":["7926736"],"is_preprint":false},{"year":1995,"finding":"Sep1/Xrn1 is an abundant cytoplasmic protein (~80,000 molecules/diploid cell); >90% is cytoplasmic by cell fractionation and indirect immunofluorescence, supporting a role in cytoplasmic RNA metabolism rather than nuclear processes.","method":"Cell fractionation, indirect immunofluorescence, quantitative immunoblot","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — direct subcellular fractionation and immunofluorescence with quantification, replicated by other studies","pmids":["7739553"],"is_preprint":false},{"year":1995,"finding":"sep1 (xrn1) ski2 and sep1 (xrn1) ski3 double mutants are synthetically lethal in a manner independent of killer viruses, and sep1 ski2/ski3 double mutants arrest in late G1 at Start; this places XRN1 and the SKI complex in parallel pathways controlling translation on transcripts targeted for degradation.","method":"Genetic epistasis, synthetic lethality screen, temperature-sensitive allele analysis, cell cycle arrest characterization","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic epistasis with defined cell-cycle arrest phenotype, virus-independent confirmation, replicated","pmids":["7739552"],"is_preprint":false},{"year":1995,"finding":"Sep1/Xrn1 promotes polymerization of porcine brain and yeast tubulin into microtubules in vitro and co-sediments with microtubules; sep1 mutants show increased benomyl sensitivity, chromosome loss, karyogamy defect, and impaired spindle pole body separation; genetic interaction with tubulin genes supports a role as a microtubule-associated protein.","method":"In vitro tubulin polymerization assay, sucrose cushion co-sedimentation, benomyl sensitivity assay, genetic double mutants with tubulin genes","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro reconstitution of microtubule polymerization plus co-sedimentation plus genetic epistasis, three orthogonal approaches in one study","pmids":["7720696"],"is_preprint":false},{"year":1995,"finding":"N-terminal sequences of Sep1/Xrn1 are essential for complementing slow growth and benomyl hypersensitivity, while at least 270 C-terminal amino acids are dispensable; the essential sequences correspond to regions conserved with the S. pombe Exo2 homolog.","method":"N- and C-terminal deletion analysis, plasmid complementation of null mutant","journal":"Chromosoma","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — systematic deletion mutagenesis with defined phenotypic readout, single lab","pmids":["8529461"],"is_preprint":false},{"year":1995,"finding":"sep1 mutants arrest in pachytene during meiotic prophase with normal synaptonemal complex; the arrest is RAD9-independent; sep1 is deficient in meiotic double-strand break repair, and sep1 dmc1 and sep1 rad51 double mutants virtually eliminate pop-out recombination, indicating parallel recombination pathways.","method":"Electron microscopy of meiotic spreads, physical assay of recombination intermediates, genetic epistasis with rad51/dmc1","journal":"Genetics","confidence":"High","confidence_rationale":"Tier 2 / Strong — direct EM analysis, physical recombination assay, and genetic epistasis in one study","pmids":["7713413"],"is_preprint":false},{"year":1997,"finding":"XRN1 5'→3' exoribonucleolytic hydrolysis is stalled by oligo(G) tracts and strong secondary structures in RNA; poly(A) binding protein inhibits XRN1 hydrolysis of poly(A) but does not affect the related HKE1; stem-loop structures near the 5' end cause greater inhibition of HKE1 than XRN1.","method":"In vitro 5'→3' exoribonuclease assay with defined RNA substrates containing secondary structures, protein competition experiments","journal":"Biochemical and biophysical research communications","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro biochemical assay with defined substrates and controls, multiple structural variants tested","pmids":["9207242"],"is_preprint":false},{"year":1998,"finding":"Human XRN1 (hSEP1) protein is localized in the cytoplasm, as determined by cytochemical analysis and Western blot of fractionated cellular extracts.","method":"Subcellular fractionation, Western blot, cytochemical analysis","journal":"DNA research","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — direct fractionation experiment, single lab, single study","pmids":["9802570"],"is_preprint":false},{"year":2000,"finding":"Genetic synthetic lethality between xrn1Δ and cdc33 (eIF4E) or ceg1 (guanylyltransferase) mutations indicates that XRN1-mediated mRNA turnover pathway is functionally linked to proper mRNA capping and eIF4E–eIF4G interaction; blocking XRN1 enhances the requirement for 7mG caps and cap-recognition complex.","method":"Synthetic lethality screen, genetic epistasis, high-copy suppression analysis","journal":"Genetics","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — genetic epistasis with defined synthetic lethality, single lab","pmids":["10790382"],"is_preprint":false},{"year":2004,"finding":"The C. elegans 5'→3' exoribonuclease xrn-1 is required for ventral epithelial enclosure during embryogenesis; RNAi knockdown of xrn-1 results in failure of epithelial closure, establishing a role for the 5'→3' mRNA decay pathway in morphogenesis.","method":"RNAi knockdown of xrn-1 in C. elegans, embryonic phenotype analysis","journal":"RNA (New York, N.Y.)","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — clean knockdown with specific developmental phenotype, single lab, RNAi only","pmids":["14681585"],"is_preprint":false},{"year":2005,"finding":"In Drosophila cells, 3' mRNA fragments generated by RISC cleavage are degraded from their 5' ends by XRN1, while 5' fragments are degraded by the exosome; this establishes XRN1 as the nuclease responsible for degrading the 3' products of siRNA-directed cleavage.","method":"RNAi depletion of XRN1 and exosome components in Drosophila S2 cells, RNA blot detection of RISC cleavage intermediates","journal":"RNA (New York, N.Y.)","confidence":"High","confidence_rationale":"Tier 2 / Moderate — genetic depletion with specific RNA intermediate detection, clear directional decay established by two complementary depletions","pmids":["15703439"],"is_preprint":false},{"year":2008,"finding":"XRN1 (along with Rat1) is a component of the rapid tRNA decay (RTD) pathway that degrades hypomodified mature tRNA species in yeast; deletion of XRN1 and RAT1 prevents both degradation and deacylation of hypomodified tRNA(Val(AAC)) and rescues temperature-sensitive growth.","method":"Genetic deletion of XRN1, RAT1, and MET22 in trm8Δ trm4Δ strains, Northern blot for tRNA levels, aminoacylation assays, growth phenotype analysis","journal":"Genes & development","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple genetic deletions with direct tRNA stability measurements and multiple tRNA substrates tested","pmids":["18443146"],"is_preprint":false},{"year":2008,"finding":"The 20S RNA narnavirus 5'-end strong secondary structure (G-rich, buried stem) enables it to evade SKI1/XRN1-mediated degradation; mutations that weaken this structure make the virus vulnerable to XRN1, demonstrating that RNA secondary structure at the 5' end is the molecular basis of XRN1 resistance.","method":"XRN1 overexpression and deletion in yeast, mutational analysis of viral 5'-stem structure, viral copy number measurement","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — mutagenesis of substrate coupled with in vivo XRN1 activity assay, mechanistic structure-function demonstrated","pmids":["18640978"],"is_preprint":false},{"year":2010,"finding":"An RNA pseudoknot (PSK3) in the yellow fever virus 3' UTR is required for stalling the host XRN1 exonuclease and producing sfRNA; the pseudoknot was confirmed by structure probing and mutagenesis; the stalling element alone is sufficient to direct sfRNA-like RNA production from a heterologous vector.","method":"In vitro XRN1 degradation assay with purified XRN1, RNA structure probing, mutagenesis, 5' end sequencing of sfRNA, heterologous expression","journal":"Journal of virology","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro reconstitution with purified XRN1, mutagenesis, and in vivo sfRNA production confirmed","pmids":["20739539"],"is_preprint":false},{"year":2011,"finding":"Crystal structure of Xrn1 in complex with a substrate reveals that the 5'-terminal trinucleotide stacks between aromatic side chains while a highly basic pocket specifically recognizes the 5' phosphate; mutations in residues binding the 5'-terminal nucleotide impair Xrn1 processivity; the mechanism couples processive hydrolysis to duplex melting for substrates with single-stranded 5' overhangs.","method":"X-ray crystallography of Xrn1–substrate complex, site-directed mutagenesis of binding residues, in vitro processivity and activity assays","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 1 / Strong — crystal structure plus mutagenesis plus in vitro activity assay, mechanistic basis of 5'-monophosphate specificity and processivity established","pmids":["21362555"],"is_preprint":false},{"year":2011,"finding":"Crystal structure of Kluyveromyces lactis Xrn1 (residues 1–1245, E178Q mutant) shows that the two conserved XRN regions form the active site, and that a unique 510-residue segment (absent from Rat1/Xrn2) contains four domains (D1–D4) that stabilize the N-terminal segment conformation and likely serve as a platform for protein partners; mutagenesis confirms functional importance of D1–D4 for activity.","method":"X-ray crystallography, site-directed mutagenesis, in vitro biochemical activity assays","journal":"Nature structural & molecular biology","confidence":"High","confidence_rationale":"Tier 1 / Strong — crystal structure combined with mutagenesis and biochemical validation","pmids":["21297639"],"is_preprint":false},{"year":2011,"finding":"XRN1 is recruited to translating mRNAs following SOX-induced internal cleavage by the Kaposi's sarcoma-associated herpesvirus host shutoff factor, and degrades the resulting fragments; SOX co-sediments with translation initiation complexes and cleaved intermediates accumulate in the 40S fraction, indicating XRN1 degrades mRNAs during translation.","method":"Polysome sedimentation, RNA blot detection of cleavage intermediates, XRN1 depletion, co-sedimentation analysis","journal":"PLoS pathogens","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — XRN1 depletion with intermediate detection and polysome fractionation, two orthogonal methods","pmids":["22046136"],"is_preprint":false},{"year":2012,"finding":"XRN1 directly interacts with DCP1 in Drosophila cells and with EDC4 in human cells, coupling mRNA decapping to 5'→3' degradation; the interaction is mediated by the DCP1 EVH1 domain binding a DCP1-binding motif (DBM) in XRN1's C-terminal region, as revealed by NMR structure.","method":"Co-immunoprecipitation, NMR structure of DCP1 EVH1 domain bound to XRN1 DBM peptide, in vivo interaction mapping","journal":"Nature structural & molecular biology","confidence":"High","confidence_rationale":"Tier 1 / Strong — NMR structure of the interaction interface plus reciprocal co-IP in two species","pmids":["23142987"],"is_preprint":false},{"year":2012,"finding":"Flavivirus sfRNA formation inhibits XRN1 activity in Dengue- and Kunjin virus-infected cells; XRN1 repression results in accumulation of uncapped mRNAs and increased overall cellular mRNA stability; a mutant Kunjin virus unable to form sfRNA does not affect host mRNA stability or XRN1 activity.","method":"Viral infection with sfRNA-null mutant virus, sfRNA expression in absence of infection, XRN1 activity assays, mRNA stability measurements, detection of uncapped mRNA intermediates","journal":"RNA (New York, N.Y.)","confidence":"High","confidence_rationale":"Tier 2 / Strong — sfRNA mutant virus used to directly demonstrate sfRNA-dependent XRN1 inhibition, multiple orthogonal approaches","pmids":["23006624"],"is_preprint":false},{"year":2012,"finding":"HCV RNA replication is degraded primarily by XRN1 in infected cells; XRN1 knockdown enhances HCV replication and miR-122 supplementation and XRN1 knockdown have equal, redundant, nonadditive effects on viral RNA decay, indicating miR-122 protects HCV RNA specifically from XRN1-mediated 5' decay.","method":"XRN1 siRNA knockdown, miR-122 supplementation, viral RNA decay assays, sequencing of 5' and 3' RNA degradation intermediates in infected cells","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 / Strong — siRNA knockdown with directional decay intermediate sequencing and miR-122 epistasis analysis, multiple orthogonal approaches","pmids":["23248316"],"is_preprint":false},{"year":2012,"finding":"Dcs1 (scavenger decapping enzyme) functions as a specific cofactor of Xrn1 in yeast: Dcs1 improves the apparent affinity of Xrn1 for RNA and forms a complex with Xrn1 in vitro; Xrn1 is essentially inactive in the absence of Dcs1 in vivo; this activation is required for mitochondrial respiration (growth on glycerol).","method":"In vitro RNA binding and exoribonuclease assays with purified proteins, co-IP, in vivo growth assays, 2D protein gel analysis of deletion strains","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro reconstitution of Dcs1-Xrn1 complex, cofactor activity demonstrated biochemically and validated in vivo","pmids":["22570495"],"is_preprint":false},{"year":2013,"finding":"Global mRNA level buffering in yeast requires Xrn1: in strains lacking mRNA degradation factors, changes in degradation rates are compensated by changes in synthesis rates, but this buffering is abolished in xrn1Δ strains, indicating Xrn1 is required for the feedback coupling between mRNA decay and transcription.","method":"Comparative dynamic transcriptome analysis (cDTA) with metabolic RNA labeling in 46 yeast mutant strains","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 2 / Strong — genome-wide quantitative transcriptome analysis across many mutants, Xrn1 requirement confirmed as specific vs other decay factors","pmids":["24119399"],"is_preprint":false},{"year":2014,"finding":"Dengue virus sfRNA is produced by XRN1 loading at the 5' end of genomic RNA and processively degrading ~10 kb, stalling at two independently-folded RNA structures organized around a three-way junction; disrupting the junction's fold eliminates sfRNA production in human cells infected with flavivirus.","method":"Real-time in vitro XRN1 resistance assay, RNA mutagenesis, RNA folding analysis, cell-based sfRNA detection in flavivirus-infected human cells","journal":"eLife","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro XRN1 assay with mutagenesis linked directly to in vivo sfRNA production in human cells","pmids":["24692447"],"is_preprint":false},{"year":2015,"finding":"XRN1 depletion in vaccinia virus-infected cells leads to accumulation of double-stranded RNA (dsRNA) and activation of PKR and OAS/RNase L innate immune effectors; XRN1 is therefore a cellular factor regulating dsRNA accumulation and dsRNA-responsive innate immunity, and is required for VacV growth.","method":"siRNA depletion of XRN1 in VacV-infected cells, dsRNA quantification, PKR and OAS pathway activation assays, viral growth assays","journal":"Cell host & microbe","confidence":"High","confidence_rationale":"Tier 2 / Moderate — siRNA knockdown with direct dsRNA quantification and innate immune pathway activation measurements, mechanism established","pmids":["25766294"],"is_preprint":false},{"year":2015,"finding":"XRN1 co-localizes with post-synaptic structures in neurons as discrete 'synaptic XRN1 bodies' (SX-bodies) distinct from P-bodies or stress granules; NMDA receptor stimulation increases SX-body size and number while decreasing local translation, and XRN1 knockdown impairs NMDA-triggered translational repression.","method":"Fluorescence microscopy in primary neurons, XRN1 siRNA knockdown, synaptic stimulation assays (NMDA, mGluR), local translation measurements","journal":"Journal of cell science","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct localization imaging with functional knockdown linking XRN1 bodies to translational repression, single lab","pmids":["25736288"],"is_preprint":false},{"year":2015,"finding":"In Drosophila, null mutation in pacman/xrn1 increases expression of pro-apoptotic mRNAs hid and reaper at the post-transcriptional level; the null phenotype (small imaginal discs, pupal lethality) is rescued by deletion removing one copy of reaper/hid/grim, placing Pacman/XRN1 in the apoptotic pathway by targeting these mRNAs for degradation.","method":"Drosophila genetic null mutation, rescue by pro-apoptotic gene deletion, quantitative RT-PCR of hid and reaper mRNAs, pre-mRNA analysis to confirm post-transcriptional regulation","journal":"Biology open","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic epistasis via rescue experiment, with direct mRNA level measurements distinguishing transcriptional vs post-transcriptional regulation","pmids":["25836675"],"is_preprint":false},{"year":2015,"finding":"Xrn1 accumulates at plasma membrane-associated eisosomes after glucose exhaustion (post-diauxic shift) in yeast, dependent on eisosome components Pil1 and Sur7; this sequestration is not accompanied by other mRNA-decay machinery components and Xrn1 is released from eisosomes by glucose addition.","method":"Fluorescence microscopy of GFP-tagged Xrn1, genetic deletion of PIL1 and SUR7, glucose addition experiments","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct live-cell imaging with genetic controls, functional consequence linked to mRNA decay regulation","pmids":["25811606"],"is_preprint":false},{"year":2017,"finding":"Yeast Pat1 C-terminal region directly interacts with a helical leucine-rich motif (HLM) in the C-terminal region of yeast Xrn1, as revealed by structural analysis of Pat1-HLM complexes; this interaction surface also recruits Dcp2, and ability to bind HLMs is required for efficient growth and normal mRNA decay.","method":"Co-immunoprecipitation, X-ray crystallography of Pat1-HLM complex, in vivo mRNA decay assays, growth assays","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 / Moderate — crystal structure of the interaction domain plus in vivo functional validation with defined phenotype","pmids":["29078363"],"is_preprint":false},{"year":2017,"finding":"Xrn1 sequestration at eisosomes during post-diauxic shift in yeast inhibits Xrn1-mediated mRNA degradation; eisosome-associated Xrn1 retains its enzymatic functionality and is re-activated upon glucose addition; cells lacking eisosome organizer Pil1 retain Xrn1 mRNA decay activity into stationary phase.","method":"mRNA decay assays in wild-type and pil1Δ strains, glucose addition experiments, Xrn1 localization tracking","journal":"European journal of cell biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct mRNA decay measurements linked to Xrn1 localization, functional rescue by glucose, single lab","pmids":["28501103"],"is_preprint":false},{"year":2017,"finding":"Xrn1 physically interacts with the Gag protein of the L-A totivirus in S. cerevisiae, and XRN1 has evolved under positive natural selection in Saccharomyces with sequence differences that translate to species-specific antiviral activity against cognate L-A viruses.","method":"Co-immunoprecipitation of Xrn1 with L-A Gag protein, phylogenetic analysis of positive selection, cross-species complementation experiments with different Xrn1 orthologs","journal":"PLoS pathogens","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct Co-IP of Xrn1-Gag interaction, species-specific activity validated across multiple orthologs, single lab","pmids":["27711183"],"is_preprint":false},{"year":2017,"finding":"RNA structures in the 3'-terminal portion of the Rift Valley fever virus N mRNA and in ambisense transcripts of arenaviruses can stall and repress XRN1; the phlebovirus stalling element likely forms a G-quadruplex structure.","method":"In vitro XRN1 stalling biochemical assays, mutagenesis, G-quadruplex prediction","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 1 / Weak — in vitro XRN1 assay with multiple viral substrates, single lab, G-quadruplex mechanism not fully confirmed","pmids":["29118186"],"is_preprint":false},{"year":2017,"finding":"Xrn1 promotes ssDNA generation at uncapped telomeres and is necessary for DNA damage checkpoint activation upon telomere uncapping; Xrn1 also maintains telomere length by promoting Cdc13 association with telomeres independently of ssDNA generation, and downregulates the Rif1 telomerase-inhibitor transcript.","method":"Genetic deletion of XRN1, telomere length assays, checkpoint activation assays, ChIP for Cdc13 association, RNA levels analysis","journal":"Nucleic acids research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple distinct telomere phenotypes established by genetic deletion with direct molecular measurements, single lab","pmids":["28160602"],"is_preprint":false},{"year":2018,"finding":"The m6A reader YTHDC2 directly interacts with XRN1 via its ankyrin repeat domains in an RNA-independent manner; this interaction recruits XRN1 to m6A-containing mRNAs, promoting their degradation, while the YTH and R3H domains of YTHDC2 also contribute to RNA binding.","method":"Co-immunoprecipitation (RNA-independent conditions), domain mapping (ankyrin repeat deletions), CRAC analysis, YTH domain binding assay","journal":"RNA (New York, N.Y.)","confidence":"High","confidence_rationale":"Tier 2 / Moderate — RNA-independent Co-IP with domain mapping, CRAC for RNA interactions, multiple orthogonal methods","pmids":["29970596"],"is_preprint":false},{"year":2018,"finding":"The DNA damage checkpoint kinase Rad53 directly phosphorylates Xrn1 in vitro; Xrn1 was the most enriched substrate in a phosphoproteomic screen for Rad53 targets; phosphorylation of Xrn1 by Rad53 does not affect Xrn1's intrinsic nuclease activity in vitro but may affect activity or specificity in vivo.","method":"Mass spectrometry-based phosphoproteomic screen, in vitro kinase assay with Rad53 and Xrn1, in vitro nuclease activity assay","journal":"G3 (Bethesda, Md.)","confidence":"Medium","confidence_rationale":"Tier 1 / Weak — in vitro kinase assay confirmed, but in vivo functional consequence of phosphorylation not established","pmids":["30377154"],"is_preprint":false},{"year":2018,"finding":"XRN1 is a post-transcriptional negative regulator of autophagy in both yeast and mammalian cells; XRN1 deletion in yeast enhances autophagy and upregulates ATG transcripts via its ribonuclease activity; in mammalian cells, XRN1 siRNA depletion enhances autophagy and picornavirus replication.","method":"Chromosomal deletion of XRN1, autophagy assays (autophagosome formation), ATG transcript level measurement, catalytic mutant analysis, siRNA depletion in mammalian cells","journal":"Autophagy","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic deletion with autophagy readout, catalytic mutant distinguishes enzymatic requirement, confirmed in two model systems","pmids":["29465287"],"is_preprint":false},{"year":2019,"finding":"Cryo-EM structure of the S. cerevisiae 80S ribosome–Xrn1 complex reveals that Xrn1 binds at the mRNA exit site of the ribosome via its conserved core; mRNA is channelled directly from the ribosomal decoding site into the Xrn1 active center, separated by only 17 ± 1 nucleotides, enabling co-translational mRNA decay.","method":"Cryo-electron microscopy structure determination of programmed 80S ribosome–Xrn1 complex","journal":"Nature structural & molecular biology","confidence":"High","confidence_rationale":"Tier 1 / Strong — high-resolution cryo-EM structure with direct visualization of the ribosome-Xrn1 interface and mRNA channel","pmids":["30911188"],"is_preprint":false},{"year":2019,"finding":"A low-complexity C-terminal region of human XRN1 (CIR) directly interacts with the CCR4-NOT deadenylase complex and with the decapping activator PatL1; CIR overexpression represses reporter mRNA deadenylation in human cells and inhibits CCR4-NOT and CAF1 deadenylase activity in vitro; PatL1 binding to CIR alleviates CIR-mediated inhibition of CCR4-NOT.","method":"In vitro deadenylase activity assay with purified proteins, reporter mRNA deadenylation assay in XRN1-null cell line complementation, direct binding assays","journal":"Nucleic acids research","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro reconstitution of inhibition activity, complementation in null cell line, multiple interacting partners mapped","pmids":["31340047"],"is_preprint":false},{"year":2019,"finding":"Xrn1 promotes translation of a specific group of transcripts encoding membrane proteins via interactions with components of the translation initiation machinery and correlates with Xrn1-dependence for mRNA localization at the endoplasmic reticulum; for this group, Xrn1 stimulates transcription, mRNA translation, and decay.","method":"Transcriptome-wide ribosome profiling, polysome analysis, ER fractionation, biochemical interaction studies with translation initiation factors","journal":"Nature communications","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — transcriptome-wide translation analysis combined with biochemical interaction studies and ER localization fractionation, single lab","pmids":["30899024"],"is_preprint":false},{"year":2019,"finding":"Xrn1 modulates RNA polymerase II (Pol II) transcription initiation and elongation; NET-seq in xrn1Δ yeast shows reduced Pol II occupancy downstream of transcription start sites and increased Pol II accumulation near cleavage/polyadenylation sites with features of backtracked Pol II; Xrn1 functions mainly as a transcriptional activator.","method":"Native elongating transcript sequencing (NET-seq), mathematical modeling of transcription rates in xrn1Δ yeast","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — genome-wide Pol II occupancy mapping in KO strain, single lab, mechanism proposed from sequencing data","pmids":["32518159"],"is_preprint":false},{"year":2020,"finding":"Xrn1 biochemically associates with eisosomal proteins specifically after the post-diauxic shift in yeast but not during exponential growth; decapping complex and Lsm1-7/Pat1 complex do not associate with eisosomal proteins under the same conditions, indicating selective sequestration of Xrn1.","method":"Tandem affinity purification (TAP) and mass spectrometry in different growth phases, biochemical co-purification","journal":"microPublication biology","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — direct biochemical co-purification in defined growth states, single lab, complements prior microscopy work","pmids":["37746059"],"is_preprint":false},{"year":2021,"finding":"Xrn1 is a NAD cap decapping (deNADding) enzyme: it releases intact NAD from NAD-capped RNAs and subsequently degrades the RNA; a deNADding-deficient Xrn1 mutant that retains 5'-monophosphate exonuclease activity reveals that Xrn1 deNADding is required for normal growth on non-fermenting sugar and modulates mitochondrial NAD-capped RNA levels.","method":"In vitro NAD cap decapping assay with Xrn1, deNADding-deficient point mutant generation, growth phenotype analysis on glycerol, mitochondrial RNA fractionation and analysis","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro enzymatic characterization with separation-of-function mutant, in vivo phenotype distinguishing deNADding from exonuclease activity","pmids":["35173156"],"is_preprint":false},{"year":2021,"finding":"Measles virus (MeV) hijacks XRN1 by translocating it to cytoplasmic inclusion bodies (IBs) where viral replication occurs; XRN1 at IBs degrades dsRNA, suppressing PKR-ISR pathway activation and facilitating viral replication; XRN1 knockout increases dsRNA accumulation, PKR activation, and suppresses MeV replication.","method":"Immunofluorescence localization of XRN1 in MeV-infected cells, XRN1 knockout, dsRNA immunofluorescence, PKR phosphorylation assays, viral replication assays","journal":"Journal of virology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — KO with direct dsRNA measurement and PKR pathway activation, localization confirmed by immunofluorescence, single lab","pmids":["36300942"],"is_preprint":false},{"year":2021,"finding":"XRN1 directly interacts with NS1 protein of influenza A virus (IAV) and co-localizes with NS1 in P-bodies; XRN1 suppresses RIG-I-mediated IFN-β production; XRN1 depletion impairs viral replication and enhances innate immune response, while overexpression increases viral titers.","method":"Co-immunoprecipitation of XRN1 and NS1, co-localization immunofluorescence, XRN1 knockdown/knockout and overexpression, IFN-β mRNA and p-IRF3 quantification, viral titer assays","journal":"mBio","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP plus knockdown/overexpression with direct IFN pathway measurements, single lab","pmids":["34311580"],"is_preprint":false},{"year":2022,"finding":"The 3'→5' RNA helicase activity of YTHDC2 is essential for mouse fertility; this helicase activity is enhanced by YTHDC2's interaction with XRN1; loss of helicase activity (catalytic-dead mutant, dominant negative) causes infertility with mixed mitotic/meiotic transcriptome identity in germ cells.","method":"Mouse genetic knockin of catalytic-dead YTHDC2 helicase mutation, biochemical in vitro helicase assay with and without XRN1, single-cell transcriptomics, zebrafish ythdc2 mutant analysis","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro biochemical reconstitution of XRN1-enhanced helicase activity, multiple in vivo genetic models (mouse and zebrafish), single-cell transcriptomics","pmids":["35305312"],"is_preprint":false},{"year":2023,"finding":"Disrupting the EDC4–XRN1 interaction or altering their stoichiometry in human cells inhibits mRNA decapping and stabilizes microRNA-targeted mRNAs in a translationally repressed state; this leads to larger P-bodies that prevent mRNA decapping; P-bodies support cell viability and prevent stress granule formation when XRN1 is limiting.","method":"Disruption of EDC4-XRN1 interaction (domain mutants), reporter mRNA decay assays, P-body size/number quantification by microscopy, stress granule formation assay, XRN1-null cell line complementation","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 2 / Strong — interaction disruption with specific mRNA reporter decay measurements, P-body quantification, and cell viability assays, multiple orthogonal approaches","pmids":["37621215"],"is_preprint":false},{"year":2024,"finding":"XRN1 depletion activates the dsRNA sensor RIG-I/MAVS pathway and IFN signaling by causing accumulation of cytosolic dsRNA from endogenous retroelements (Alus); XRN1 is an essential gene for survival of a subset of cancer cells with high ISG expression, and this dependency is mediated by PKR and MAVS signaling.","method":"CRISPR-based XRN1 deletion in cancer cell lines, dsRNA quantification, RIG-I/MAVS knockdown epistasis, pan-cancer CRISPR screen analysis, dsRNA-inducing drug combination","journal":"Cell reports","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — KO with direct dsRNA measurement and pathway epistasis, two independent studies published same year, single lab for each","pmids":["38261511"],"is_preprint":false},{"year":2024,"finding":"XRN1 deletion causes PKR pathway activation and cancer cell lethality in cells with high interferon-stimulated gene (ISG) expression; XRN1 depletion causes accumulation of endogenous complementary sense/anti-sense RNAs as candidate PKR ligands; JAK1/2 inhibition (reducing PKR levels) rescues sensitivity to XRN1 deletion.","method":"XRN1 CRISPR deletion, PKR pathway activation assays, ruxolitinib rescue experiment, IFN-β stimulation sensitization experiment, endogenous dsRNA sequencing","journal":"Cell reports","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — KO with pathway epistasis and drug rescue, dsRNA candidate identification, single lab","pmids":["38261514"],"is_preprint":false}],"current_model":"XRN1 is a highly conserved, processive 5'→3' exoribonuclease that degrades 5'-monophosphorylated cytoplasmic RNAs—including decapped mRNAs, siRNA/miRNA-cleaved fragments, and hypomodified tRNAs—using a catalytic mechanism requiring divalent metal ions and a highly basic 5'-phosphate recognition pocket (established by crystal structures); it is recruited to mRNA substrates via direct protein–protein interactions with decapping factors DCP1/EDC4, the CCR4-NOT deadenylase complex (through its low-complexity CIR region), and the m6A reader YTHDC2 (through ankyrin repeats), and physically docks at the mRNA exit site of translating ribosomes (cryo-EM structure) to perform co-translational mRNA decay; additionally, XRN1 is regulated by cofactor Dcs1, post-translationally phosphorylated by the Rad53 DNA damage kinase, and can be enzymatically repressed or sequestered by flaviviral xrRNA structures, eisosome localization, and viral proteins (NS1, MeV nucleocapsid), and it also functions as a deNADding enzyme for NAD-capped RNAs, as a microtubule polymerization factor (in yeast), and as a negative regulator of autophagy and dsRNA-induced innate immune responses (PKR/RIG-I/MAVS pathways) by preventing accumulation of endogenous dsRNA."},"narrative":{"mechanistic_narrative":"XRN1 is a highly conserved, processive cytoplasmic 5'→3' exoribonuclease that constitutes the central engine of the 5'→3' mRNA decay pathway and broadly controls cytoplasmic RNA turnover [PMID:1398123, PMID:8417335]. First identified in yeast as a non-essential gene whose loss slows growth and stabilizes short-lived mRNAs [PMID:1979303, PMID:1398123], it is an abundant, predominantly cytoplasmic enzyme conserved through to human XRN1 [PMID:7739553, PMID:9802570]. Crystal structures of fungal Xrn1 define its catalytic basis: a highly basic pocket specifically recognizes the substrate 5'-monophosphate while the 5'-terminal nucleotides stack between aromatic residues, coupling processive hydrolysis to duplex melting, and a unique multi-domain insertion absent from the nuclear paralog Rat1/Xrn2 forms a platform for protein partners [PMID:21362555, PMID:21297639]. Its degradative activity is intrinsically blocked by 5'-proximal RNA secondary structures, a property exploited by flaviviral xrRNA elements (pseudoknots and three-way-junction folds) that stall the enzyme to generate subgenomic sfRNA and globally repress host decay [PMID:9207242, PMID:20739539, PMID:24692447, PMID:23006624]. XRN1 acts on a wide substrate range, degrading decapped mRNAs, the 3' products of RISC/siRNA cleavage, hypomodified tRNAs of the rapid tRNA decay pathway, and—via a separable deNADding activity—NAD-capped RNAs [PMID:15703439, PMID:18443146, PMID:35173156]. Substrate engagement is governed by direct protein interactions: a C-terminal DCP1-binding motif couples decapping to degradation through DCP1/EDC4, a low-complexity CIR region binds the CCR4-NOT deadenylase complex and PatL1/Pat1, and the m6A reader YTHDC2 recruits XRN1 to methylated transcripts through its ankyrin repeats [PMID:23142987, PMID:31340047, PMID:29078363, PMID:29970596]. A cryo-EM structure of the ribosome–Xrn1 complex shows the enzyme docked at the mRNA exit channel with the decoding site only ~17 nucleotides from its active center, establishing co-translational mRNA decay [PMID:30911188]. Beyond turnover, XRN1 couples decay to transcription as a buffering factor required for synthesis–degradation feedback and modulates Pol II elongation [PMID:24119399, PMID:32518159], and it serves as a negative regulator of autophagy and of dsRNA-triggered innate immunity, where its loss permits accumulation of endogenous dsRNA from retroelements that activates PKR and RIG-I/MAVS signaling—a dependency that renders ISG-high cancer cells reliant on XRN1 [PMID:29465287, PMID:38261511, PMID:38261514, PMID:25766294]. The yeast protein additionally promotes microtubule polymerization, meiotic recombination, and telomere homeostasis [PMID:7720696, PMID:1840632, PMID:28160602].","teleology":[{"year":1990,"claim":"Established that XRN1 is a 5'→3' exoribonuclease whose loss is tolerated but growth-limiting, defining it as a non-essential RNA-degrading enzyme.","evidence":"Gene disruption and plasmid complementation in yeast with hydrolytic activity assay","pmids":["1979303"],"confidence":"High","gaps":["No in vivo RNA substrate defined","Catalytic mechanism not resolved"]},{"year":1992,"claim":"Linked XRN1 directly to mRNA turnover by showing deletion stabilizes specific short-lived mRNAs, establishing its role in cytoplasmic decay.","evidence":"Northern measurement of mRNA half-lives in xrn1Δ yeast","pmids":["1398123"],"confidence":"High","gaps":["Recruitment to substrates unknown","Genome-wide substrate scope undefined"]},{"year":1991,"claim":"Reported that the protein promotes homologous DNA strand exchange and is required for meiotic recombination, raising the question of a moonlighting nuclear/DNA function.","evidence":"In vitro strand exchange with purified protein plus sep1 meiotic mutant analysis","pmids":["1840632"],"confidence":"High","gaps":["Relationship between DNA pairing and exoribonuclease activity unclear","In vivo relevance to recombination mechanism not separated from RNA roles"]},{"year":1993,"claim":"Distinguished cytoplasmic XRN1 from its essential nuclear paralog Rat1/Hke1 and showed they are non-redundant, partitioning 5'→3' decay into two compartments.","evidence":"In vitro activity assays, immunodepletion, and complementation failure in yeast","pmids":["8417335"],"confidence":"High","gaps":["Structural basis of compartment-specific function unknown"]},{"year":1994,"claim":"Showed the DNA pairing (paranemic joint) activity is independent of exonuclease activity, separating the two biochemical functions.","evidence":"Filter binding, EM, and in vitro pairing with exonuclease controls","pmids":["7926736"],"confidence":"High","gaps":["Physiological role of DNA pairing in vivo unresolved"]},{"year":1995,"claim":"Localized Xrn1 predominantly to the cytoplasm and quantified its high abundance, anchoring its primary role in cytoplasmic RNA metabolism.","evidence":"Cell fractionation, immunofluorescence, and quantitative immunoblot in yeast","pmids":["7739553"],"confidence":"High","gaps":["Nuclear pool function not characterized"]},{"year":1995,"claim":"Placed XRN1 and the SKI complex in parallel pathways controlling fate of degradation-targeted transcripts via synthetic lethality and a G1/Start arrest.","evidence":"Genetic epistasis and synthetic lethality in yeast double mutants","pmids":["7739552"],"confidence":"High","gaps":["Molecular basis of the parallel pathway relationship not defined"]},{"year":1995,"claim":"Demonstrated a microtubule-associated activity, showing Xrn1 promotes tubulin polymerization and supports spindle/karyogamy functions in yeast.","evidence":"In vitro tubulin polymerization, co-sedimentation, and genetic interaction with tubulin genes","pmids":["7720696"],"confidence":"High","gaps":["Whether microtubule role is conserved beyond yeast unknown","Relationship to nuclease activity unclear"]},{"year":1995,"claim":"Mapped the essential, conserved N-terminal region of Xrn1 versus a dispensable C-terminus, beginning structure–function dissection.","evidence":"N- and C-terminal deletion complementation in yeast","pmids":["8529461"],"confidence":"Medium","gaps":["Specific catalytic residues not yet identified","Single-lab deletion analysis"]},{"year":1995,"claim":"Connected XRN1-mediated decay to meiotic double-strand break repair through a recombination pathway parallel to Rad51/Dmc1.","evidence":"EM of meiotic spreads, physical recombination assays, and genetic epistasis","pmids":["7713413"],"confidence":"High","gaps":["Direct mechanism of Xrn1 in DSB repair unresolved"]},{"year":1997,"claim":"Defined the biochemical sensitivity of Xrn1 to 5'-proximal secondary structure and oligo(G) tracts, a property later central to viral evasion.","evidence":"In vitro exoribonuclease assays with structured RNA substrates and PABP competition","pmids":["9207242"],"confidence":"High","gaps":["Structural basis of stalling not yet visualized"]},{"year":1998,"claim":"Confirmed conservation by localizing human XRN1 (hSEP1) to the cytoplasm.","evidence":"Subcellular fractionation and Western blot of human cells","pmids":["9802570"],"confidence":"Medium","gaps":["Human substrate repertoire not addressed","Single study"]},{"year":2000,"claim":"Linked XRN1 decay function to capping and cap-recognition machinery through synthetic lethality with eIF4E and guanylyltransferase mutants.","evidence":"Synthetic lethality and high-copy suppression in yeast","pmids":["10790382"],"confidence":"Medium","gaps":["Direct physical coupling to cap complex not shown here"]},{"year":2003,"claim":"Extended XRN1 function to development, showing the 5'→3' decay pathway is required for epithelial morphogenesis.","evidence":"RNAi knockdown of xrn-1 in C. elegans embryos","pmids":["14681585"],"confidence":"Medium","gaps":["Target mRNAs driving the morphogenesis defect unknown","RNAi-only evidence"]},{"year":2005,"claim":"Identified XRN1 as the nuclease degrading the 3' products of RISC/siRNA-directed cleavage, integrating it into the RNAi pathway.","evidence":"RNAi depletion of XRN1 vs exosome in Drosophila S2 cells with intermediate detection","pmids":["15703439"],"confidence":"High","gaps":["Recruitment to RISC products not defined"]},{"year":2008,"claim":"Showed XRN1 participates in rapid tRNA decay of hypomodified tRNAs, broadening its substrate range beyond mRNA.","evidence":"Genetic deletions in trm8Δ trm4Δ strains with tRNA stability and aminoacylation assays","pmids":["18443146"],"confidence":"High","gaps":["How hypomodified tRNAs become XRN1 substrates mechanistically unclear"]},{"year":2008,"claim":"Established 5'-end RNA secondary structure as the molecular basis of XRN1 resistance using a narnavirus model.","evidence":"XRN1 overexpression/deletion and mutational analysis of viral 5' stem in yeast","pmids":["18640978"],"confidence":"High","gaps":["High-resolution structure of the stalling element not determined here"]},{"year":2010,"claim":"Defined the flaviviral xrRNA principle: a 3' UTR pseudoknot stalls XRN1 to generate sfRNA, the first defined RNA element that halts the processive enzyme.","evidence":"In vitro degradation with purified XRN1, structure probing, mutagenesis, and heterologous sfRNA production","pmids":["20739539"],"confidence":"High","gaps":["Atomic structure of stalled XRN1–xrRNA complex not resolved"]},{"year":2011,"claim":"Solved the catalytic mechanism: structures revealed 5'-monophosphate recognition by a basic pocket and aromatic stacking driving processivity and coupled duplex melting.","evidence":"X-ray crystallography of Xrn1–substrate plus mutagenesis and processivity assays","pmids":["21362555","21297639"],"confidence":"High","gaps":["Conformational dynamics during processive translocation not captured","Partner-binding platform interactions inferred structurally but not all validated"]},{"year":2011,"claim":"Showed viral host-shutoff (KSHV SOX) recruits XRN1 to translating mRNAs, linking endonucleolytic cleavage to XRN1 degradation during translation.","evidence":"Polysome sedimentation and XRN1 depletion with cleavage-intermediate detection","pmids":["22046136"],"confidence":"Medium","gaps":["Direct XRN1–ribosome contact not yet structurally shown at this stage"]},{"year":2012,"claim":"Identified the direct decapping–decay coupling: an XRN1 DCP1-binding motif engages DCP1/EDC4 to hand off decapped mRNAs.","evidence":"Co-IP and NMR structure of DCP1 EVH1–XRN1 DBM in fly and human cells","pmids":["23142987"],"confidence":"High","gaps":["Stoichiometry and dynamics of the handoff in vivo not fully defined"]},{"year":2012,"claim":"Established that flaviviral sfRNA represses XRN1 to globally stabilize host mRNAs during infection.","evidence":"sfRNA-null mutant virus with XRN1 activity and mRNA stability measurements","pmids":["23006624"],"confidence":"High","gaps":["Quantitative impact on specific host transcripts not delineated"]},{"year":2012,"claim":"Showed miR-122 protects HCV RNA specifically from XRN1-mediated 5' decay, defining XRN1 as a major restriction nuclease antagonized by a host miRNA.","evidence":"siRNA knockdown, miR-122 supplementation, and decay-intermediate sequencing in infected cells","pmids":["23248316"],"confidence":"High","gaps":["Mechanism of miR-122 5'-end shielding not structurally defined"]},{"year":2012,"claim":"Identified Dcs1 as an essential cofactor that activates Xrn1 by improving RNA affinity, required for respiratory growth.","evidence":"In vitro reconstitution with purified Xrn1/Dcs1, co-IP, and in vivo growth assays","pmids":["22570495"],"confidence":"High","gaps":["Structural basis of Dcs1 activation not resolved","Whether a mammalian equivalent exists not addressed"]},{"year":2013,"claim":"Demonstrated Xrn1 is specifically required for the global mRNA buffering that couples decay rates to transcription, revealing a decay-to-synthesis feedback role.","evidence":"Comparative dynamic transcriptome analysis across 46 yeast decay mutants","pmids":["24119399"],"confidence":"High","gaps":["Molecular signal transmitting decay status to transcription unknown"]},{"year":2014,"claim":"Resolved the dengue xrRNA architecture, showing XRN1 stalls at a three-way-junction fold after processively degrading ~10 kb.","evidence":"Real-time in vitro XRN1 resistance assays, mutagenesis, and cell-based sfRNA detection","pmids":["24692447"],"confidence":"High","gaps":["Generality across all flaviviral xrRNAs not established here"]},{"year":2015,"claim":"Defined XRN1 as a regulator of endogenous dsRNA and dsRNA-responsive innate immunity, since its depletion activates PKR and OAS/RNase L.","evidence":"siRNA depletion in vaccinia-infected cells with dsRNA and pathway activation assays","pmids":["25766294"],"confidence":"High","gaps":["Source of accumulating dsRNA not identified at this stage"]},{"year":2015,"claim":"Revealed neuronal synaptic XRN1 bodies coupling XRN1 to activity-dependent local translational repression.","evidence":"Imaging in primary neurons with synaptic stimulation and XRN1 knockdown","pmids":["25736288"],"confidence":"Medium","gaps":["Target mRNAs and decay vs sequestration roles in SX-bodies unclear","Single lab"]},{"year":2015,"claim":"Connected Pacman/XRN1 to apoptosis by targeting pro-apoptotic hid and reaper mRNAs for degradation in Drosophila.","evidence":"Null mutant, rescue by pro-apoptotic gene deletion, and pre-mRNA/mRNA quantification","pmids":["25836675"],"confidence":"High","gaps":["Whether mammalian XRN1 regulates apoptotic transcripts similarly not addressed"]},{"year":2015,"claim":"Showed glucose-regulated eisosome sequestration of Xrn1 inhibits its decay activity, defining a reversible spatial control mechanism.","evidence":"Live-cell imaging of GFP-Xrn1 with PIL1/SUR7 deletion and glucose addition","pmids":["25811606"],"confidence":"Medium","gaps":["Signal triggering eisosome recruitment not defined","Single lab"]},{"year":2017,"claim":"Mapped the Pat1–Xrn1 interaction via a helical leucine-rich motif shared with Dcp2, integrating Xrn1 into the decapping-activator network.","evidence":"Crystallography of Pat1–HLM, co-IP, and in vivo mRNA decay assays","pmids":["29078363"],"confidence":"High","gaps":["Competition between HLM partners in vivo not quantified"]},{"year":2017,"claim":"Confirmed eisosome-sequestered Xrn1 is enzymatically intact and reactivated by glucose, establishing sequestration as a storage rather than degradation mechanism.","evidence":"mRNA decay assays in wild-type and pil1Δ strains with glucose addition","pmids":["28501103"],"confidence":"Medium","gaps":["Physiological advantage of sequestration not quantified","Single lab"]},{"year":2017,"claim":"Showed Xrn1 physically engages totivirus Gag and is under positive selection, defining a species-specific antiviral arms race.","evidence":"Co-IP of Xrn1–Gag, phylogenetic selection analysis, and cross-species complementation","pmids":["27711183"],"confidence":"Medium","gaps":["Functional consequence of Gag binding on Xrn1 activity unclear","Single lab"]},{"year":2017,"claim":"Extended XRN1-stalling RNA elements to bunyaviral/arenaviral structures, including a candidate G-quadruplex.","evidence":"In vitro XRN1 stalling assays with viral substrates and mutagenesis","pmids":["29118186"],"confidence":"Medium","gaps":["G-quadruplex mechanism not confirmed structurally","Single lab"]},{"year":2017,"claim":"Implicated Xrn1 in telomere homeostasis, promoting checkpoint activation, Cdc13 loading, and Rif1 transcript downregulation.","evidence":"Genetic deletion with telomere length, checkpoint, ChIP, and RNA assays","pmids":["28160602"],"confidence":"Medium","gaps":["Whether telomere roles depend on RNA decay activity not fully separated","Single lab"]},{"year":2018,"claim":"Defined the YTHDC2–XRN1 interaction through ankyrin repeats, recruiting XRN1 to m6A-marked mRNAs for degradation.","evidence":"RNA-independent co-IP, domain mapping, and CRAC analysis","pmids":["29970596"],"confidence":"High","gaps":["In vivo extent of m6A-directed XRN1 decay not quantified"]},{"year":2018,"claim":"Showed the DNA damage kinase Rad53 phosphorylates Xrn1, linking decay to checkpoint signaling, though intrinsic nuclease activity was unchanged in vitro.","evidence":"Phosphoproteomic screen and in vitro kinase plus nuclease assays","pmids":["30377154"],"confidence":"Medium","gaps":["In vivo functional consequence of phosphorylation not established","Phosphosites' effect on specificity untested"]},{"year":2018,"claim":"Established XRN1 as a post-transcriptional negative regulator of autophagy via its ribonuclease activity in yeast and mammals.","evidence":"Chromosomal deletion, catalytic mutant analysis, and siRNA depletion with autophagy assays","pmids":["29465287"],"confidence":"Medium","gaps":["Direct ATG transcript targeting mechanism not fully defined","Single lab"]},{"year":2019,"claim":"Provided the structural basis for co-translational decay by visualizing Xrn1 docked at the ribosomal mRNA exit site ~17 nt from the decoding center.","evidence":"Cryo-EM of programmed 80S ribosome–Xrn1 complex","pmids":["30911188"],"confidence":"High","gaps":["How Xrn1 couples to ribosome speed/quality control not resolved"]},{"year":2019,"claim":"Mapped the low-complexity CIR region of human XRN1 as a direct binder and inhibitor of CCR4-NOT and PatL1, coupling deadenylation to decay.","evidence":"In vitro deadenylase assays with purified proteins and reporter decay in XRN1-null complementation","pmids":["31340047"],"confidence":"High","gaps":["Physiological role of CIR-mediated deadenylase inhibition in vivo unclear"]},{"year":2019,"claim":"Revealed a positive role for Xrn1 in translation and ER localization of a subset of membrane-protein mRNAs, coupling synthesis, translation, and decay.","evidence":"Ribosome profiling, polysome analysis, ER fractionation, and interaction studies","pmids":["30899024"],"confidence":"Medium","gaps":["Mechanism distinguishing stimulatory from degradative roles unclear","Single lab"]},{"year":2020,"claim":"Extended Xrn1's gene-expression coupling to transcription, showing it modulates Pol II initiation and elongation as an activator.","evidence":"NET-seq and transcription rate modeling in xrn1Δ yeast","pmids":["32518159"],"confidence":"Medium","gaps":["Direct mechanism connecting cytoplasmic Xrn1 to nuclear Pol II unknown","Single lab"]},{"year":2021,"claim":"Identified a separable deNADding activity by which Xrn1 removes intact NAD caps from RNAs, required for non-fermentative growth.","evidence":"In vitro NAD-cap decapping with a separation-of-function mutant and growth/mitochondrial RNA analysis","pmids":["35173156"],"confidence":"High","gaps":["Whether deNADding occurs in mammalian XRN1 not addressed here"]},{"year":2021,"claim":"Showed measles virus relocalizes XRN1 to inclusion bodies to degrade dsRNA and suppress the PKR-ISR pathway, aiding replication.","evidence":"Immunofluorescence localization, XRN1 knockout, dsRNA and PKR phosphorylation assays","pmids":["36300942"],"confidence":"Medium","gaps":["Mechanism of XRN1 translocation to inclusion bodies unclear","Single lab"]},{"year":2021,"claim":"Showed influenza NS1 directly binds XRN1, which suppresses RIG-I-mediated IFN-β, defining a viral co-option of XRN1's immune-dampening role.","evidence":"Co-IP, co-localization, knockdown/overexpression, and IFN-β/p-IRF3 assays","pmids":["34311580"],"confidence":"Medium","gaps":["Whether NS1 alters XRN1 catalytic activity unclear","Single lab"]},{"year":2022,"claim":"Demonstrated XRN1 enhances the YTHDC2 3'→5' helicase activity essential for fertility, integrating XRN1 into germ-cell mitotic-to-meiotic transition control.","evidence":"In vitro helicase reconstitution with XRN1 plus mouse and zebrafish genetic models","pmids":["35305312"],"confidence":"High","gaps":["Mechanism by which XRN1 stimulates helicase activity unresolved"]},{"year":2023,"claim":"Showed the EDC4–XRN1 interaction controls decapping flux and P-body homeostasis, with disruption stabilizing miRNA-targeted mRNAs and enlarging P-bodies.","evidence":"Interaction-disrupting mutants, reporter decay, P-body/stress-granule imaging, and null-cell complementation","pmids":["37621215"],"confidence":"High","gaps":["How XRN1 stoichiometry sets P-body size mechanistically unclear"]},{"year":2024,"claim":"Established that XRN1 prevents accumulation of endogenous Alu-derived cytosolic dsRNA, defining XRN1 dependency in ISG-high cancers via PKR and RIG-I/MAVS.","evidence":"CRISPR deletion, dsRNA quantification, pathway epistasis, drug rescue, and pan-cancer screen analysis","pmids":["38261511","38261514"],"confidence":"Medium","gaps":["Precise endogenous dsRNA species driving PKR vs MAVS not fully resolved","Therapeutic window in tumors untested"]},{"year":null,"claim":"How XRN1's many context-specific roles—co-translational decay, decay-transcription buffering, deNADding, dsRNA surveillance, and partner-directed recruitment—are integrated and differentially regulated in human cells remains unresolved.","evidence":"No single study in the corpus reconciles XRN1's multiple activities under a unified regulatory framework","pmids":[],"confidence":"Low","gaps":["No structure of the human ribosome–XRN1 complex","Regulation of XRN1 partner choice (DCP1/EDC4 vs CCR4-NOT vs YTHDC2) in vivo not defined","In vivo significance of Rad53 phosphorylation and mammalian cofactor equivalents of Dcs1 unknown"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140098","term_label":"catalytic activity, acting on RNA","supporting_discovery_ids":[0,1,3,10,14,15,18,44]},{"term_id":"GO:0016787","term_label":"hydrolase activity","supporting_discovery_ids":[0,18,44]},{"term_id":"GO:0003723","term_label":"RNA binding","supporting_discovery_ids":[10,18,24]},{"term_id":"GO:0003677","term_label":"DNA binding","supporting_discovery_ids":[2,4]},{"term_id":"GO:0008092","term_label":"cytoskeletal protein binding","supporting_discovery_ids":[7]}],"localization":[{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[5,11]},{"term_id":"GO:0005840","term_label":"ribosome","supporting_discovery_ids":[39]},{"term_id":"GO:0005886","term_label":"plasma membrane","supporting_discovery_ids":[30,43]},{"term_id":"GO:0005783","term_label":"endoplasmic reticulum","supporting_discovery_ids":[41]}],"pathway":[{"term_id":"R-HSA-8953854","term_label":"Metabolism of RNA","supporting_discovery_ids":[1,14,15,21,39,40,44]},{"term_id":"R-HSA-74160","term_label":"Gene expression (Transcription)","supporting_discovery_ids":[25,42]},{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[27,46,49,50]},{"term_id":"R-HSA-9612973","term_label":"Autophagy","supporting_discovery_ids":[38]},{"term_id":"R-HSA-1643685","term_label":"Disease","supporting_discovery_ids":[22,23,45,46,49]}],"complexes":[],"partners":["DCP1","EDC4","PATL1/PAT1","CCR4-NOT","YTHDC2","DCS1","NS1"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q8IZH2","full_name":"5'-3' exoribonuclease 1","aliases":["Strand-exchange protein 1 homolog"],"length_aa":1706,"mass_kda":194.1,"function":"Major 5'-3' exoribonuclease involved in mRNA decay (PubMed:18172165, PubMed:33472058). Required for the 5'-3'-processing of the G4 tetraplex-containing DNA and RNA substrates (By similarity). The kinetic of hydrolysis is faster for G4 RNA tetraplex than for G4 DNA tetraplex and monomeric RNA tetraplex (By similarity). Plays a role in replication-dependent histone mRNA degradation (PubMed:18172165). 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virology","url":"https://pubmed.ncbi.nlm.nih.gov/36300942","citation_count":11,"is_preprint":false},{"pmid":"33064973","id":"PMC_33064973","title":"Xrn1-resistant RNA structures are well-conserved within the genus flavivirus.","date":"2020","source":"RNA biology","url":"https://pubmed.ncbi.nlm.nih.gov/33064973","citation_count":10,"is_preprint":false},{"pmid":"34869601","id":"PMC_34869601","title":"Processing of RNA Containing 8-Oxo-7,8-Dihydroguanosine (8-oxoG) by the Exoribonuclease Xrn-1.","date":"2021","source":"Frontiers in molecular biosciences","url":"https://pubmed.ncbi.nlm.nih.gov/34869601","citation_count":10,"is_preprint":false},{"pmid":"12952437","id":"PMC_12952437","title":"Trypsin/alpha-amylase inhibitors inactivate the endogenous barley/malt serine endoproteinase SEP-1.","date":"2003","source":"Journal of agricultural and food chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/12952437","citation_count":10,"is_preprint":false},{"pmid":"34643435","id":"PMC_34643435","title":"Zinc Finger Protein ZFP36L1 Inhibits Flavivirus Infection by both 5'-3' XRN1 and 3'-5' RNA-Exosome RNA Decay Pathways.","date":"2021","source":"Journal of virology","url":"https://pubmed.ncbi.nlm.nih.gov/34643435","citation_count":9,"is_preprint":false},{"pmid":"9218715","id":"PMC_9218715","title":"Cloning and characterization of mouse Dhm2 cDNA, a functional homolog of budding yeast SEP1.","date":"1997","source":"Gene","url":"https://pubmed.ncbi.nlm.nih.gov/9218715","citation_count":9,"is_preprint":false},{"pmid":"34646989","id":"PMC_34646989","title":"Neuronal XRN1 is required for maintenance of whole-body metabolic homeostasis.","date":"2021","source":"iScience","url":"https://pubmed.ncbi.nlm.nih.gov/34646989","citation_count":9,"is_preprint":false},{"pmid":"37667796","id":"PMC_37667796","title":"The RNA helicases Dbp2 and Mtr4 regulate the expression of Xrn1-sensitive long non-coding RNAs in yeast.","date":"2023","source":"Frontiers in RNA research","url":"https://pubmed.ncbi.nlm.nih.gov/37667796","citation_count":8,"is_preprint":false},{"pmid":"33858294","id":"PMC_33858294","title":"All genera of Flaviviridae host a conserved Xrn1-resistant RNA motif.","date":"2021","source":"RNA biology","url":"https://pubmed.ncbi.nlm.nih.gov/33858294","citation_count":8,"is_preprint":false},{"pmid":"7543408","id":"PMC_7543408","title":"Use of monoclonal antibodies in the functional characterization of the Saccharomyces cerevisiae Sep1 protein.","date":"1995","source":"European journal of biochemistry","url":"https://pubmed.ncbi.nlm.nih.gov/7543408","citation_count":8,"is_preprint":false},{"pmid":"33511416","id":"PMC_33511416","title":"Solid-phase XRN1 reactions for RNA cleavage: application in single-molecule sequencing.","date":"2021","source":"Nucleic acids 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biology","url":"https://pubmed.ncbi.nlm.nih.gov/33258404","citation_count":6,"is_preprint":false},{"pmid":"9802570","id":"PMC_9802570","title":"Cloning and characterization of human Sep1 (hSEP1) gene and cytoplasmic localization of its product.","date":"1998","source":"DNA research : an international journal for rapid publication of reports on genes and genomes","url":"https://pubmed.ncbi.nlm.nih.gov/9802570","citation_count":5,"is_preprint":false},{"pmid":"33103962","id":"PMC_33103962","title":"sORF-Encoded Polypeptide SEP1 Is a Novel Virulence Factor of Phytophthora Pathogens.","date":"2021","source":"Molecular plant-microbe interactions : MPMI","url":"https://pubmed.ncbi.nlm.nih.gov/33103962","citation_count":5,"is_preprint":false},{"pmid":"37749116","id":"PMC_37749116","title":"Xrn1-resistant RNA motifs are disseminated throughout the RNA virome and are able to block scanning ribosomes.","date":"2023","source":"Scientific reports","url":"https://pubmed.ncbi.nlm.nih.gov/37749116","citation_count":4,"is_preprint":false},{"pmid":"32316250","id":"PMC_32316250","title":"Effects of 5'-3' Exonuclease Xrn1 on Cell Size, Proliferation and Division, and mRNA Levels of Periodic Genes in Cryptococcus neoformans.","date":"2020","source":"Genes","url":"https://pubmed.ncbi.nlm.nih.gov/32316250","citation_count":4,"is_preprint":false},{"pmid":"37746059","id":"PMC_37746059","title":"Xrn1 biochemically associates with eisosome proteins after the post diauxic shift in yeast.","date":"2023","source":"microPublication biology","url":"https://pubmed.ncbi.nlm.nih.gov/37746059","citation_count":4,"is_preprint":false},{"pmid":"39972499","id":"PMC_39972499","title":"The zinc finger protein ZFP36L2 inhibits flavivirus infection via the 5'-3' XRN1-mediated RNA decay pathway in the replication complexes.","date":"2025","source":"Journal of biomedical science","url":"https://pubmed.ncbi.nlm.nih.gov/39972499","citation_count":3,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":46614,"output_tokens":12239,"usd":0.161714,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":23633,"output_tokens":10590,"usd":0.191458,"stage2_stop_reason":"end_turn"},"total_usd":0.353172,"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\": 1990,\n      \"finding\": \"XRN1 encodes a 5'→3' exoribonuclease in yeast; disruption of the gene is not lethal but markedly reduces cell growth rate, which is rescued by reintroduction of XRN1 on a plasmid.\",\n      \"method\": \"Gene disruption (knockout) in haploid yeast, complementation with plasmid-borne XRN1, poly(A) hydrolytic activity assay, immunoreactivity\",\n      \"journal\": \"Gene\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — clean KO with defined phenotype, enzymatic activity confirmed, complementation rescue, replicated in subsequent work\",\n      \"pmids\": [\"1979303\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1992,\n      \"finding\": \"XRN1 (also known as DST2/SEP1/KEM1/RAR5) encodes a 160-kDa 5'→3' exoribonuclease; xrn1-deleted yeast cells show 2–4-fold longer half-lives of specific short-lived mRNAs, increased cellular protein levels, and reduced rRNA synthesis rate, demonstrating XRN1's key role in mRNA turnover.\",\n      \"method\": \"Gene sequencing, gene disruption, Northern analysis of specific mRNA half-lives, metabolic labeling, PAGE analysis\",\n      \"journal\": \"Gene\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — direct measurement of mRNA half-lives in KO strain, multiple orthogonal methods, replicated across studies\",\n      \"pmids\": [\"1398123\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1991,\n      \"finding\": \"The SEP1 (XRN1) protein promotes homologous DNA pairing (strand exchange) in vitro and is required in meiosis; sep1 mutants show reduced meiotic recombination and defective sporulation, with arrest after commitment to recombination but before meiosis I.\",\n      \"method\": \"Gene cloning, protein overproduction and purification, in vitro strand exchange assay, mutant phenotype analysis (sporulation, recombination)\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro reconstitution of strand exchange activity plus genetic loss-of-function with defined meiotic phenotype\",\n      \"pmids\": [\"1840632\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1993,\n      \"finding\": \"XRN1/KEM1 encodes the major cytoplasmic 5'→3' exoribonuclease (p175); its essential nuclear paralog HKE1/RAT1 encodes a related 5'→3' exoribonuclease (p116); overexpression of XRN1 p175 cannot rescue loss of HKE1/RAT1, indicating non-redundant functions.\",\n      \"method\": \"Gene cloning, in vitro 5'→3' exoribonuclease activity assay, immunodepletion, complementation test\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro enzymatic activity demonstrated, immunoreactive RNase activity abolished with specific antiserum, complementation failure established non-redundancy\",\n      \"pmids\": [\"8417335\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1994,\n      \"finding\": \"Sep1 (XRN1) promotes paranemic joint formation between homologous DNA molecules in vitro; the pairing does not require net intertwining and requires as little as 41 bp of homology; the exonuclease activity of Sep1 is not responsible for the joint.\",\n      \"method\": \"Nitrocellulose filter binding assay, electron microscopy, in vitro DNA pairing with defined substrates, exonuclease activity controls\",\n      \"journal\": \"Genes & development\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — reconstituted in vitro pairing activity with multiple structural methods and controls ruling out exonuclease as mechanism\",\n      \"pmids\": [\"7926736\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1995,\n      \"finding\": \"Sep1/Xrn1 is an abundant cytoplasmic protein (~80,000 molecules/diploid cell); >90% is cytoplasmic by cell fractionation and indirect immunofluorescence, supporting a role in cytoplasmic RNA metabolism rather than nuclear processes.\",\n      \"method\": \"Cell fractionation, indirect immunofluorescence, quantitative immunoblot\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — direct subcellular fractionation and immunofluorescence with quantification, replicated by other studies\",\n      \"pmids\": [\"7739553\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1995,\n      \"finding\": \"sep1 (xrn1) ski2 and sep1 (xrn1) ski3 double mutants are synthetically lethal in a manner independent of killer viruses, and sep1 ski2/ski3 double mutants arrest in late G1 at Start; this places XRN1 and the SKI complex in parallel pathways controlling translation on transcripts targeted for degradation.\",\n      \"method\": \"Genetic epistasis, synthetic lethality screen, temperature-sensitive allele analysis, cell cycle arrest characterization\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic epistasis with defined cell-cycle arrest phenotype, virus-independent confirmation, replicated\",\n      \"pmids\": [\"7739552\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1995,\n      \"finding\": \"Sep1/Xrn1 promotes polymerization of porcine brain and yeast tubulin into microtubules in vitro and co-sediments with microtubules; sep1 mutants show increased benomyl sensitivity, chromosome loss, karyogamy defect, and impaired spindle pole body separation; genetic interaction with tubulin genes supports a role as a microtubule-associated protein.\",\n      \"method\": \"In vitro tubulin polymerization assay, sucrose cushion co-sedimentation, benomyl sensitivity assay, genetic double mutants with tubulin genes\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro reconstitution of microtubule polymerization plus co-sedimentation plus genetic epistasis, three orthogonal approaches in one study\",\n      \"pmids\": [\"7720696\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1995,\n      \"finding\": \"N-terminal sequences of Sep1/Xrn1 are essential for complementing slow growth and benomyl hypersensitivity, while at least 270 C-terminal amino acids are dispensable; the essential sequences correspond to regions conserved with the S. pombe Exo2 homolog.\",\n      \"method\": \"N- and C-terminal deletion analysis, plasmid complementation of null mutant\",\n      \"journal\": \"Chromosoma\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — systematic deletion mutagenesis with defined phenotypic readout, single lab\",\n      \"pmids\": [\"8529461\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1995,\n      \"finding\": \"sep1 mutants arrest in pachytene during meiotic prophase with normal synaptonemal complex; the arrest is RAD9-independent; sep1 is deficient in meiotic double-strand break repair, and sep1 dmc1 and sep1 rad51 double mutants virtually eliminate pop-out recombination, indicating parallel recombination pathways.\",\n      \"method\": \"Electron microscopy of meiotic spreads, physical assay of recombination intermediates, genetic epistasis with rad51/dmc1\",\n      \"journal\": \"Genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — direct EM analysis, physical recombination assay, and genetic epistasis in one study\",\n      \"pmids\": [\"7713413\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"XRN1 5'→3' exoribonucleolytic hydrolysis is stalled by oligo(G) tracts and strong secondary structures in RNA; poly(A) binding protein inhibits XRN1 hydrolysis of poly(A) but does not affect the related HKE1; stem-loop structures near the 5' end cause greater inhibition of HKE1 than XRN1.\",\n      \"method\": \"In vitro 5'→3' exoribonuclease assay with defined RNA substrates containing secondary structures, protein competition experiments\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro biochemical assay with defined substrates and controls, multiple structural variants tested\",\n      \"pmids\": [\"9207242\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"Human XRN1 (hSEP1) protein is localized in the cytoplasm, as determined by cytochemical analysis and Western blot of fractionated cellular extracts.\",\n      \"method\": \"Subcellular fractionation, Western blot, cytochemical analysis\",\n      \"journal\": \"DNA research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — direct fractionation experiment, single lab, single study\",\n      \"pmids\": [\"9802570\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"Genetic synthetic lethality between xrn1Δ and cdc33 (eIF4E) or ceg1 (guanylyltransferase) mutations indicates that XRN1-mediated mRNA turnover pathway is functionally linked to proper mRNA capping and eIF4E–eIF4G interaction; blocking XRN1 enhances the requirement for 7mG caps and cap-recognition complex.\",\n      \"method\": \"Synthetic lethality screen, genetic epistasis, high-copy suppression analysis\",\n      \"journal\": \"Genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — genetic epistasis with defined synthetic lethality, single lab\",\n      \"pmids\": [\"10790382\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"The C. elegans 5'→3' exoribonuclease xrn-1 is required for ventral epithelial enclosure during embryogenesis; RNAi knockdown of xrn-1 results in failure of epithelial closure, establishing a role for the 5'→3' mRNA decay pathway in morphogenesis.\",\n      \"method\": \"RNAi knockdown of xrn-1 in C. elegans, embryonic phenotype analysis\",\n      \"journal\": \"RNA (New York, N.Y.)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — clean knockdown with specific developmental phenotype, single lab, RNAi only\",\n      \"pmids\": [\"14681585\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"In Drosophila cells, 3' mRNA fragments generated by RISC cleavage are degraded from their 5' ends by XRN1, while 5' fragments are degraded by the exosome; this establishes XRN1 as the nuclease responsible for degrading the 3' products of siRNA-directed cleavage.\",\n      \"method\": \"RNAi depletion of XRN1 and exosome components in Drosophila S2 cells, RNA blot detection of RISC cleavage intermediates\",\n      \"journal\": \"RNA (New York, N.Y.)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic depletion with specific RNA intermediate detection, clear directional decay established by two complementary depletions\",\n      \"pmids\": [\"15703439\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"XRN1 (along with Rat1) is a component of the rapid tRNA decay (RTD) pathway that degrades hypomodified mature tRNA species in yeast; deletion of XRN1 and RAT1 prevents both degradation and deacylation of hypomodified tRNA(Val(AAC)) and rescues temperature-sensitive growth.\",\n      \"method\": \"Genetic deletion of XRN1, RAT1, and MET22 in trm8Δ trm4Δ strains, Northern blot for tRNA levels, aminoacylation assays, growth phenotype analysis\",\n      \"journal\": \"Genes & development\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple genetic deletions with direct tRNA stability measurements and multiple tRNA substrates tested\",\n      \"pmids\": [\"18443146\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"The 20S RNA narnavirus 5'-end strong secondary structure (G-rich, buried stem) enables it to evade SKI1/XRN1-mediated degradation; mutations that weaken this structure make the virus vulnerable to XRN1, demonstrating that RNA secondary structure at the 5' end is the molecular basis of XRN1 resistance.\",\n      \"method\": \"XRN1 overexpression and deletion in yeast, mutational analysis of viral 5'-stem structure, viral copy number measurement\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — mutagenesis of substrate coupled with in vivo XRN1 activity assay, mechanistic structure-function demonstrated\",\n      \"pmids\": [\"18640978\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"An RNA pseudoknot (PSK3) in the yellow fever virus 3' UTR is required for stalling the host XRN1 exonuclease and producing sfRNA; the pseudoknot was confirmed by structure probing and mutagenesis; the stalling element alone is sufficient to direct sfRNA-like RNA production from a heterologous vector.\",\n      \"method\": \"In vitro XRN1 degradation assay with purified XRN1, RNA structure probing, mutagenesis, 5' end sequencing of sfRNA, heterologous expression\",\n      \"journal\": \"Journal of virology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro reconstitution with purified XRN1, mutagenesis, and in vivo sfRNA production confirmed\",\n      \"pmids\": [\"20739539\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Crystal structure of Xrn1 in complex with a substrate reveals that the 5'-terminal trinucleotide stacks between aromatic side chains while a highly basic pocket specifically recognizes the 5' phosphate; mutations in residues binding the 5'-terminal nucleotide impair Xrn1 processivity; the mechanism couples processive hydrolysis to duplex melting for substrates with single-stranded 5' overhangs.\",\n      \"method\": \"X-ray crystallography of Xrn1–substrate complex, site-directed mutagenesis of binding residues, in vitro processivity and activity assays\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — crystal structure plus mutagenesis plus in vitro activity assay, mechanistic basis of 5'-monophosphate specificity and processivity established\",\n      \"pmids\": [\"21362555\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Crystal structure of Kluyveromyces lactis Xrn1 (residues 1–1245, E178Q mutant) shows that the two conserved XRN regions form the active site, and that a unique 510-residue segment (absent from Rat1/Xrn2) contains four domains (D1–D4) that stabilize the N-terminal segment conformation and likely serve as a platform for protein partners; mutagenesis confirms functional importance of D1–D4 for activity.\",\n      \"method\": \"X-ray crystallography, site-directed mutagenesis, in vitro biochemical activity assays\",\n      \"journal\": \"Nature structural & molecular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — crystal structure combined with mutagenesis and biochemical validation\",\n      \"pmids\": [\"21297639\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"XRN1 is recruited to translating mRNAs following SOX-induced internal cleavage by the Kaposi's sarcoma-associated herpesvirus host shutoff factor, and degrades the resulting fragments; SOX co-sediments with translation initiation complexes and cleaved intermediates accumulate in the 40S fraction, indicating XRN1 degrades mRNAs during translation.\",\n      \"method\": \"Polysome sedimentation, RNA blot detection of cleavage intermediates, XRN1 depletion, co-sedimentation analysis\",\n      \"journal\": \"PLoS pathogens\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — XRN1 depletion with intermediate detection and polysome fractionation, two orthogonal methods\",\n      \"pmids\": [\"22046136\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"XRN1 directly interacts with DCP1 in Drosophila cells and with EDC4 in human cells, coupling mRNA decapping to 5'→3' degradation; the interaction is mediated by the DCP1 EVH1 domain binding a DCP1-binding motif (DBM) in XRN1's C-terminal region, as revealed by NMR structure.\",\n      \"method\": \"Co-immunoprecipitation, NMR structure of DCP1 EVH1 domain bound to XRN1 DBM peptide, in vivo interaction mapping\",\n      \"journal\": \"Nature structural & molecular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — NMR structure of the interaction interface plus reciprocal co-IP in two species\",\n      \"pmids\": [\"23142987\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Flavivirus sfRNA formation inhibits XRN1 activity in Dengue- and Kunjin virus-infected cells; XRN1 repression results in accumulation of uncapped mRNAs and increased overall cellular mRNA stability; a mutant Kunjin virus unable to form sfRNA does not affect host mRNA stability or XRN1 activity.\",\n      \"method\": \"Viral infection with sfRNA-null mutant virus, sfRNA expression in absence of infection, XRN1 activity assays, mRNA stability measurements, detection of uncapped mRNA intermediates\",\n      \"journal\": \"RNA (New York, N.Y.)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — sfRNA mutant virus used to directly demonstrate sfRNA-dependent XRN1 inhibition, multiple orthogonal approaches\",\n      \"pmids\": [\"23006624\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"HCV RNA replication is degraded primarily by XRN1 in infected cells; XRN1 knockdown enhances HCV replication and miR-122 supplementation and XRN1 knockdown have equal, redundant, nonadditive effects on viral RNA decay, indicating miR-122 protects HCV RNA specifically from XRN1-mediated 5' decay.\",\n      \"method\": \"XRN1 siRNA knockdown, miR-122 supplementation, viral RNA decay assays, sequencing of 5' and 3' RNA degradation intermediates in infected cells\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — siRNA knockdown with directional decay intermediate sequencing and miR-122 epistasis analysis, multiple orthogonal approaches\",\n      \"pmids\": [\"23248316\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Dcs1 (scavenger decapping enzyme) functions as a specific cofactor of Xrn1 in yeast: Dcs1 improves the apparent affinity of Xrn1 for RNA and forms a complex with Xrn1 in vitro; Xrn1 is essentially inactive in the absence of Dcs1 in vivo; this activation is required for mitochondrial respiration (growth on glycerol).\",\n      \"method\": \"In vitro RNA binding and exoribonuclease assays with purified proteins, co-IP, in vivo growth assays, 2D protein gel analysis of deletion strains\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro reconstitution of Dcs1-Xrn1 complex, cofactor activity demonstrated biochemically and validated in vivo\",\n      \"pmids\": [\"22570495\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Global mRNA level buffering in yeast requires Xrn1: in strains lacking mRNA degradation factors, changes in degradation rates are compensated by changes in synthesis rates, but this buffering is abolished in xrn1Δ strains, indicating Xrn1 is required for the feedback coupling between mRNA decay and transcription.\",\n      \"method\": \"Comparative dynamic transcriptome analysis (cDTA) with metabolic RNA labeling in 46 yeast mutant strains\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genome-wide quantitative transcriptome analysis across many mutants, Xrn1 requirement confirmed as specific vs other decay factors\",\n      \"pmids\": [\"24119399\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Dengue virus sfRNA is produced by XRN1 loading at the 5' end of genomic RNA and processively degrading ~10 kb, stalling at two independently-folded RNA structures organized around a three-way junction; disrupting the junction's fold eliminates sfRNA production in human cells infected with flavivirus.\",\n      \"method\": \"Real-time in vitro XRN1 resistance assay, RNA mutagenesis, RNA folding analysis, cell-based sfRNA detection in flavivirus-infected human cells\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro XRN1 assay with mutagenesis linked directly to in vivo sfRNA production in human cells\",\n      \"pmids\": [\"24692447\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"XRN1 depletion in vaccinia virus-infected cells leads to accumulation of double-stranded RNA (dsRNA) and activation of PKR and OAS/RNase L innate immune effectors; XRN1 is therefore a cellular factor regulating dsRNA accumulation and dsRNA-responsive innate immunity, and is required for VacV growth.\",\n      \"method\": \"siRNA depletion of XRN1 in VacV-infected cells, dsRNA quantification, PKR and OAS pathway activation assays, viral growth assays\",\n      \"journal\": \"Cell host & microbe\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — siRNA knockdown with direct dsRNA quantification and innate immune pathway activation measurements, mechanism established\",\n      \"pmids\": [\"25766294\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"XRN1 co-localizes with post-synaptic structures in neurons as discrete 'synaptic XRN1 bodies' (SX-bodies) distinct from P-bodies or stress granules; NMDA receptor stimulation increases SX-body size and number while decreasing local translation, and XRN1 knockdown impairs NMDA-triggered translational repression.\",\n      \"method\": \"Fluorescence microscopy in primary neurons, XRN1 siRNA knockdown, synaptic stimulation assays (NMDA, mGluR), local translation measurements\",\n      \"journal\": \"Journal of cell science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct localization imaging with functional knockdown linking XRN1 bodies to translational repression, single lab\",\n      \"pmids\": [\"25736288\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"In Drosophila, null mutation in pacman/xrn1 increases expression of pro-apoptotic mRNAs hid and reaper at the post-transcriptional level; the null phenotype (small imaginal discs, pupal lethality) is rescued by deletion removing one copy of reaper/hid/grim, placing Pacman/XRN1 in the apoptotic pathway by targeting these mRNAs for degradation.\",\n      \"method\": \"Drosophila genetic null mutation, rescue by pro-apoptotic gene deletion, quantitative RT-PCR of hid and reaper mRNAs, pre-mRNA analysis to confirm post-transcriptional regulation\",\n      \"journal\": \"Biology open\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic epistasis via rescue experiment, with direct mRNA level measurements distinguishing transcriptional vs post-transcriptional regulation\",\n      \"pmids\": [\"25836675\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Xrn1 accumulates at plasma membrane-associated eisosomes after glucose exhaustion (post-diauxic shift) in yeast, dependent on eisosome components Pil1 and Sur7; this sequestration is not accompanied by other mRNA-decay machinery components and Xrn1 is released from eisosomes by glucose addition.\",\n      \"method\": \"Fluorescence microscopy of GFP-tagged Xrn1, genetic deletion of PIL1 and SUR7, glucose addition experiments\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct live-cell imaging with genetic controls, functional consequence linked to mRNA decay regulation\",\n      \"pmids\": [\"25811606\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Yeast Pat1 C-terminal region directly interacts with a helical leucine-rich motif (HLM) in the C-terminal region of yeast Xrn1, as revealed by structural analysis of Pat1-HLM complexes; this interaction surface also recruits Dcp2, and ability to bind HLMs is required for efficient growth and normal mRNA decay.\",\n      \"method\": \"Co-immunoprecipitation, X-ray crystallography of Pat1-HLM complex, in vivo mRNA decay assays, growth assays\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — crystal structure of the interaction domain plus in vivo functional validation with defined phenotype\",\n      \"pmids\": [\"29078363\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Xrn1 sequestration at eisosomes during post-diauxic shift in yeast inhibits Xrn1-mediated mRNA degradation; eisosome-associated Xrn1 retains its enzymatic functionality and is re-activated upon glucose addition; cells lacking eisosome organizer Pil1 retain Xrn1 mRNA decay activity into stationary phase.\",\n      \"method\": \"mRNA decay assays in wild-type and pil1Δ strains, glucose addition experiments, Xrn1 localization tracking\",\n      \"journal\": \"European journal of cell biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct mRNA decay measurements linked to Xrn1 localization, functional rescue by glucose, single lab\",\n      \"pmids\": [\"28501103\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Xrn1 physically interacts with the Gag protein of the L-A totivirus in S. cerevisiae, and XRN1 has evolved under positive natural selection in Saccharomyces with sequence differences that translate to species-specific antiviral activity against cognate L-A viruses.\",\n      \"method\": \"Co-immunoprecipitation of Xrn1 with L-A Gag protein, phylogenetic analysis of positive selection, cross-species complementation experiments with different Xrn1 orthologs\",\n      \"journal\": \"PLoS pathogens\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct Co-IP of Xrn1-Gag interaction, species-specific activity validated across multiple orthologs, single lab\",\n      \"pmids\": [\"27711183\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"RNA structures in the 3'-terminal portion of the Rift Valley fever virus N mRNA and in ambisense transcripts of arenaviruses can stall and repress XRN1; the phlebovirus stalling element likely forms a G-quadruplex structure.\",\n      \"method\": \"In vitro XRN1 stalling biochemical assays, mutagenesis, G-quadruplex prediction\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Weak — in vitro XRN1 assay with multiple viral substrates, single lab, G-quadruplex mechanism not fully confirmed\",\n      \"pmids\": [\"29118186\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Xrn1 promotes ssDNA generation at uncapped telomeres and is necessary for DNA damage checkpoint activation upon telomere uncapping; Xrn1 also maintains telomere length by promoting Cdc13 association with telomeres independently of ssDNA generation, and downregulates the Rif1 telomerase-inhibitor transcript.\",\n      \"method\": \"Genetic deletion of XRN1, telomere length assays, checkpoint activation assays, ChIP for Cdc13 association, RNA levels analysis\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple distinct telomere phenotypes established by genetic deletion with direct molecular measurements, single lab\",\n      \"pmids\": [\"28160602\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"The m6A reader YTHDC2 directly interacts with XRN1 via its ankyrin repeat domains in an RNA-independent manner; this interaction recruits XRN1 to m6A-containing mRNAs, promoting their degradation, while the YTH and R3H domains of YTHDC2 also contribute to RNA binding.\",\n      \"method\": \"Co-immunoprecipitation (RNA-independent conditions), domain mapping (ankyrin repeat deletions), CRAC analysis, YTH domain binding assay\",\n      \"journal\": \"RNA (New York, N.Y.)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — RNA-independent Co-IP with domain mapping, CRAC for RNA interactions, multiple orthogonal methods\",\n      \"pmids\": [\"29970596\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"The DNA damage checkpoint kinase Rad53 directly phosphorylates Xrn1 in vitro; Xrn1 was the most enriched substrate in a phosphoproteomic screen for Rad53 targets; phosphorylation of Xrn1 by Rad53 does not affect Xrn1's intrinsic nuclease activity in vitro but may affect activity or specificity in vivo.\",\n      \"method\": \"Mass spectrometry-based phosphoproteomic screen, in vitro kinase assay with Rad53 and Xrn1, in vitro nuclease activity assay\",\n      \"journal\": \"G3 (Bethesda, Md.)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Weak — in vitro kinase assay confirmed, but in vivo functional consequence of phosphorylation not established\",\n      \"pmids\": [\"30377154\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"XRN1 is a post-transcriptional negative regulator of autophagy in both yeast and mammalian cells; XRN1 deletion in yeast enhances autophagy and upregulates ATG transcripts via its ribonuclease activity; in mammalian cells, XRN1 siRNA depletion enhances autophagy and picornavirus replication.\",\n      \"method\": \"Chromosomal deletion of XRN1, autophagy assays (autophagosome formation), ATG transcript level measurement, catalytic mutant analysis, siRNA depletion in mammalian cells\",\n      \"journal\": \"Autophagy\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic deletion with autophagy readout, catalytic mutant distinguishes enzymatic requirement, confirmed in two model systems\",\n      \"pmids\": [\"29465287\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Cryo-EM structure of the S. cerevisiae 80S ribosome–Xrn1 complex reveals that Xrn1 binds at the mRNA exit site of the ribosome via its conserved core; mRNA is channelled directly from the ribosomal decoding site into the Xrn1 active center, separated by only 17 ± 1 nucleotides, enabling co-translational mRNA decay.\",\n      \"method\": \"Cryo-electron microscopy structure determination of programmed 80S ribosome–Xrn1 complex\",\n      \"journal\": \"Nature structural & molecular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — high-resolution cryo-EM structure with direct visualization of the ribosome-Xrn1 interface and mRNA channel\",\n      \"pmids\": [\"30911188\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"A low-complexity C-terminal region of human XRN1 (CIR) directly interacts with the CCR4-NOT deadenylase complex and with the decapping activator PatL1; CIR overexpression represses reporter mRNA deadenylation in human cells and inhibits CCR4-NOT and CAF1 deadenylase activity in vitro; PatL1 binding to CIR alleviates CIR-mediated inhibition of CCR4-NOT.\",\n      \"method\": \"In vitro deadenylase activity assay with purified proteins, reporter mRNA deadenylation assay in XRN1-null cell line complementation, direct binding assays\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro reconstitution of inhibition activity, complementation in null cell line, multiple interacting partners mapped\",\n      \"pmids\": [\"31340047\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Xrn1 promotes translation of a specific group of transcripts encoding membrane proteins via interactions with components of the translation initiation machinery and correlates with Xrn1-dependence for mRNA localization at the endoplasmic reticulum; for this group, Xrn1 stimulates transcription, mRNA translation, and decay.\",\n      \"method\": \"Transcriptome-wide ribosome profiling, polysome analysis, ER fractionation, biochemical interaction studies with translation initiation factors\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — transcriptome-wide translation analysis combined with biochemical interaction studies and ER localization fractionation, single lab\",\n      \"pmids\": [\"30899024\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Xrn1 modulates RNA polymerase II (Pol II) transcription initiation and elongation; NET-seq in xrn1Δ yeast shows reduced Pol II occupancy downstream of transcription start sites and increased Pol II accumulation near cleavage/polyadenylation sites with features of backtracked Pol II; Xrn1 functions mainly as a transcriptional activator.\",\n      \"method\": \"Native elongating transcript sequencing (NET-seq), mathematical modeling of transcription rates in xrn1Δ yeast\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — genome-wide Pol II occupancy mapping in KO strain, single lab, mechanism proposed from sequencing data\",\n      \"pmids\": [\"32518159\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Xrn1 biochemically associates with eisosomal proteins specifically after the post-diauxic shift in yeast but not during exponential growth; decapping complex and Lsm1-7/Pat1 complex do not associate with eisosomal proteins under the same conditions, indicating selective sequestration of Xrn1.\",\n      \"method\": \"Tandem affinity purification (TAP) and mass spectrometry in different growth phases, biochemical co-purification\",\n      \"journal\": \"microPublication biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — direct biochemical co-purification in defined growth states, single lab, complements prior microscopy work\",\n      \"pmids\": [\"37746059\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Xrn1 is a NAD cap decapping (deNADding) enzyme: it releases intact NAD from NAD-capped RNAs and subsequently degrades the RNA; a deNADding-deficient Xrn1 mutant that retains 5'-monophosphate exonuclease activity reveals that Xrn1 deNADding is required for normal growth on non-fermenting sugar and modulates mitochondrial NAD-capped RNA levels.\",\n      \"method\": \"In vitro NAD cap decapping assay with Xrn1, deNADding-deficient point mutant generation, growth phenotype analysis on glycerol, mitochondrial RNA fractionation and analysis\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro enzymatic characterization with separation-of-function mutant, in vivo phenotype distinguishing deNADding from exonuclease activity\",\n      \"pmids\": [\"35173156\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Measles virus (MeV) hijacks XRN1 by translocating it to cytoplasmic inclusion bodies (IBs) where viral replication occurs; XRN1 at IBs degrades dsRNA, suppressing PKR-ISR pathway activation and facilitating viral replication; XRN1 knockout increases dsRNA accumulation, PKR activation, and suppresses MeV replication.\",\n      \"method\": \"Immunofluorescence localization of XRN1 in MeV-infected cells, XRN1 knockout, dsRNA immunofluorescence, PKR phosphorylation assays, viral replication assays\",\n      \"journal\": \"Journal of virology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — KO with direct dsRNA measurement and PKR pathway activation, localization confirmed by immunofluorescence, single lab\",\n      \"pmids\": [\"36300942\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"XRN1 directly interacts with NS1 protein of influenza A virus (IAV) and co-localizes with NS1 in P-bodies; XRN1 suppresses RIG-I-mediated IFN-β production; XRN1 depletion impairs viral replication and enhances innate immune response, while overexpression increases viral titers.\",\n      \"method\": \"Co-immunoprecipitation of XRN1 and NS1, co-localization immunofluorescence, XRN1 knockdown/knockout and overexpression, IFN-β mRNA and p-IRF3 quantification, viral titer assays\",\n      \"journal\": \"mBio\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP plus knockdown/overexpression with direct IFN pathway measurements, single lab\",\n      \"pmids\": [\"34311580\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"The 3'→5' RNA helicase activity of YTHDC2 is essential for mouse fertility; this helicase activity is enhanced by YTHDC2's interaction with XRN1; loss of helicase activity (catalytic-dead mutant, dominant negative) causes infertility with mixed mitotic/meiotic transcriptome identity in germ cells.\",\n      \"method\": \"Mouse genetic knockin of catalytic-dead YTHDC2 helicase mutation, biochemical in vitro helicase assay with and without XRN1, single-cell transcriptomics, zebrafish ythdc2 mutant analysis\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro biochemical reconstitution of XRN1-enhanced helicase activity, multiple in vivo genetic models (mouse and zebrafish), single-cell transcriptomics\",\n      \"pmids\": [\"35305312\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Disrupting the EDC4–XRN1 interaction or altering their stoichiometry in human cells inhibits mRNA decapping and stabilizes microRNA-targeted mRNAs in a translationally repressed state; this leads to larger P-bodies that prevent mRNA decapping; P-bodies support cell viability and prevent stress granule formation when XRN1 is limiting.\",\n      \"method\": \"Disruption of EDC4-XRN1 interaction (domain mutants), reporter mRNA decay assays, P-body size/number quantification by microscopy, stress granule formation assay, XRN1-null cell line complementation\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — interaction disruption with specific mRNA reporter decay measurements, P-body quantification, and cell viability assays, multiple orthogonal approaches\",\n      \"pmids\": [\"37621215\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"XRN1 depletion activates the dsRNA sensor RIG-I/MAVS pathway and IFN signaling by causing accumulation of cytosolic dsRNA from endogenous retroelements (Alus); XRN1 is an essential gene for survival of a subset of cancer cells with high ISG expression, and this dependency is mediated by PKR and MAVS signaling.\",\n      \"method\": \"CRISPR-based XRN1 deletion in cancer cell lines, dsRNA quantification, RIG-I/MAVS knockdown epistasis, pan-cancer CRISPR screen analysis, dsRNA-inducing drug combination\",\n      \"journal\": \"Cell reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — KO with direct dsRNA measurement and pathway epistasis, two independent studies published same year, single lab for each\",\n      \"pmids\": [\"38261511\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"XRN1 deletion causes PKR pathway activation and cancer cell lethality in cells with high interferon-stimulated gene (ISG) expression; XRN1 depletion causes accumulation of endogenous complementary sense/anti-sense RNAs as candidate PKR ligands; JAK1/2 inhibition (reducing PKR levels) rescues sensitivity to XRN1 deletion.\",\n      \"method\": \"XRN1 CRISPR deletion, PKR pathway activation assays, ruxolitinib rescue experiment, IFN-β stimulation sensitization experiment, endogenous dsRNA sequencing\",\n      \"journal\": \"Cell reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — KO with pathway epistasis and drug rescue, dsRNA candidate identification, single lab\",\n      \"pmids\": [\"38261514\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"XRN1 is a highly conserved, processive 5'→3' exoribonuclease that degrades 5'-monophosphorylated cytoplasmic RNAs—including decapped mRNAs, siRNA/miRNA-cleaved fragments, and hypomodified tRNAs—using a catalytic mechanism requiring divalent metal ions and a highly basic 5'-phosphate recognition pocket (established by crystal structures); it is recruited to mRNA substrates via direct protein–protein interactions with decapping factors DCP1/EDC4, the CCR4-NOT deadenylase complex (through its low-complexity CIR region), and the m6A reader YTHDC2 (through ankyrin repeats), and physically docks at the mRNA exit site of translating ribosomes (cryo-EM structure) to perform co-translational mRNA decay; additionally, XRN1 is regulated by cofactor Dcs1, post-translationally phosphorylated by the Rad53 DNA damage kinase, and can be enzymatically repressed or sequestered by flaviviral xrRNA structures, eisosome localization, and viral proteins (NS1, MeV nucleocapsid), and it also functions as a deNADding enzyme for NAD-capped RNAs, as a microtubule polymerization factor (in yeast), and as a negative regulator of autophagy and dsRNA-induced innate immune responses (PKR/RIG-I/MAVS pathways) by preventing accumulation of endogenous dsRNA.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"XRN1 is a highly conserved, processive cytoplasmic 5'→3' exoribonuclease that constitutes the central engine of the 5'→3' mRNA decay pathway and broadly controls cytoplasmic RNA turnover [#1, #3]. First identified in yeast as a non-essential gene whose loss slows growth and stabilizes short-lived mRNAs [#0, #1], it is an abundant, predominantly cytoplasmic enzyme conserved through to human XRN1 [#5, #11]. Crystal structures of fungal Xrn1 define its catalytic basis: a highly basic pocket specifically recognizes the substrate 5'-monophosphate while the 5'-terminal nucleotides stack between aromatic residues, coupling processive hydrolysis to duplex melting, and a unique multi-domain insertion absent from the nuclear paralog Rat1/Xrn2 forms a platform for protein partners [#18, #19]. Its degradative activity is intrinsically blocked by 5'-proximal RNA secondary structures, a property exploited by flaviviral xrRNA elements (pseudoknots and three-way-junction folds) that stall the enzyme to generate subgenomic sfRNA and globally repress host decay [#10, #17, #26, #22]. XRN1 acts on a wide substrate range, degrading decapped mRNAs, the 3' products of RISC/siRNA cleavage, hypomodified tRNAs of the rapid tRNA decay pathway, and—via a separable deNADding activity—NAD-capped RNAs [#14, #15, #44]. Substrate engagement is governed by direct protein interactions: a C-terminal DCP1-binding motif couples decapping to degradation through DCP1/EDC4, a low-complexity CIR region binds the CCR4-NOT deadenylase complex and PatL1/Pat1, and the m6A reader YTHDC2 recruits XRN1 to methylated transcripts through its ankyrin repeats [#21, #40, #31, #36]. A cryo-EM structure of the ribosome–Xrn1 complex shows the enzyme docked at the mRNA exit channel with the decoding site only ~17 nucleotides from its active center, establishing co-translational mRNA decay [#39]. Beyond turnover, XRN1 couples decay to transcription as a buffering factor required for synthesis–degradation feedback and modulates Pol II elongation [#25, #42], and it serves as a negative regulator of autophagy and of dsRNA-triggered innate immunity, where its loss permits accumulation of endogenous dsRNA from retroelements that activates PKR and RIG-I/MAVS signaling—a dependency that renders ISG-high cancer cells reliant on XRN1 [#38, #49, #50, #27]. The yeast protein additionally promotes microtubule polymerization, meiotic recombination, and telomere homeostasis [#7, #2, #35].\",\n  \"teleology\": [\n    {\n      \"year\": 1990,\n      \"claim\": \"Established that XRN1 is a 5'→3' exoribonuclease whose loss is tolerated but growth-limiting, defining it as a non-essential RNA-degrading enzyme.\",\n      \"evidence\": \"Gene disruption and plasmid complementation in yeast with hydrolytic activity assay\",\n      \"pmids\": [\"1979303\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No in vivo RNA substrate defined\", \"Catalytic mechanism not resolved\"]\n    },\n    {\n      \"year\": 1992,\n      \"claim\": \"Linked XRN1 directly to mRNA turnover by showing deletion stabilizes specific short-lived mRNAs, establishing its role in cytoplasmic decay.\",\n      \"evidence\": \"Northern measurement of mRNA half-lives in xrn1Δ yeast\",\n      \"pmids\": [\"1398123\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Recruitment to substrates unknown\", \"Genome-wide substrate scope undefined\"]\n    },\n    {\n      \"year\": 1991,\n      \"claim\": \"Reported that the protein promotes homologous DNA strand exchange and is required for meiotic recombination, raising the question of a moonlighting nuclear/DNA function.\",\n      \"evidence\": \"In vitro strand exchange with purified protein plus sep1 meiotic mutant analysis\",\n      \"pmids\": [\"1840632\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Relationship between DNA pairing and exoribonuclease activity unclear\", \"In vivo relevance to recombination mechanism not separated from RNA roles\"]\n    },\n    {\n      \"year\": 1993,\n      \"claim\": \"Distinguished cytoplasmic XRN1 from its essential nuclear paralog Rat1/Hke1 and showed they are non-redundant, partitioning 5'→3' decay into two compartments.\",\n      \"evidence\": \"In vitro activity assays, immunodepletion, and complementation failure in yeast\",\n      \"pmids\": [\"8417335\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of compartment-specific function unknown\"]\n    },\n    {\n      \"year\": 1994,\n      \"claim\": \"Showed the DNA pairing (paranemic joint) activity is independent of exonuclease activity, separating the two biochemical functions.\",\n      \"evidence\": \"Filter binding, EM, and in vitro pairing with exonuclease controls\",\n      \"pmids\": [\"7926736\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Physiological role of DNA pairing in vivo unresolved\"]\n    },\n    {\n      \"year\": 1995,\n      \"claim\": \"Localized Xrn1 predominantly to the cytoplasm and quantified its high abundance, anchoring its primary role in cytoplasmic RNA metabolism.\",\n      \"evidence\": \"Cell fractionation, immunofluorescence, and quantitative immunoblot in yeast\",\n      \"pmids\": [\"7739553\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Nuclear pool function not characterized\"]\n    },\n    {\n      \"year\": 1995,\n      \"claim\": \"Placed XRN1 and the SKI complex in parallel pathways controlling fate of degradation-targeted transcripts via synthetic lethality and a G1/Start arrest.\",\n      \"evidence\": \"Genetic epistasis and synthetic lethality in yeast double mutants\",\n      \"pmids\": [\"7739552\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular basis of the parallel pathway relationship not defined\"]\n    },\n    {\n      \"year\": 1995,\n      \"claim\": \"Demonstrated a microtubule-associated activity, showing Xrn1 promotes tubulin polymerization and supports spindle/karyogamy functions in yeast.\",\n      \"evidence\": \"In vitro tubulin polymerization, co-sedimentation, and genetic interaction with tubulin genes\",\n      \"pmids\": [\"7720696\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether microtubule role is conserved beyond yeast unknown\", \"Relationship to nuclease activity unclear\"]\n    },\n    {\n      \"year\": 1995,\n      \"claim\": \"Mapped the essential, conserved N-terminal region of Xrn1 versus a dispensable C-terminus, beginning structure–function dissection.\",\n      \"evidence\": \"N- and C-terminal deletion complementation in yeast\",\n      \"pmids\": [\"8529461\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Specific catalytic residues not yet identified\", \"Single-lab deletion analysis\"]\n    },\n    {\n      \"year\": 1995,\n      \"claim\": \"Connected XRN1-mediated decay to meiotic double-strand break repair through a recombination pathway parallel to Rad51/Dmc1.\",\n      \"evidence\": \"EM of meiotic spreads, physical recombination assays, and genetic epistasis\",\n      \"pmids\": [\"7713413\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct mechanism of Xrn1 in DSB repair unresolved\"]\n    },\n    {\n      \"year\": 1997,\n      \"claim\": \"Defined the biochemical sensitivity of Xrn1 to 5'-proximal secondary structure and oligo(G) tracts, a property later central to viral evasion.\",\n      \"evidence\": \"In vitro exoribonuclease assays with structured RNA substrates and PABP competition\",\n      \"pmids\": [\"9207242\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of stalling not yet visualized\"]\n    },\n    {\n      \"year\": 1998,\n      \"claim\": \"Confirmed conservation by localizing human XRN1 (hSEP1) to the cytoplasm.\",\n      \"evidence\": \"Subcellular fractionation and Western blot of human cells\",\n      \"pmids\": [\"9802570\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Human substrate repertoire not addressed\", \"Single study\"]\n    },\n    {\n      \"year\": 2000,\n      \"claim\": \"Linked XRN1 decay function to capping and cap-recognition machinery through synthetic lethality with eIF4E and guanylyltransferase mutants.\",\n      \"evidence\": \"Synthetic lethality and high-copy suppression in yeast\",\n      \"pmids\": [\"10790382\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct physical coupling to cap complex not shown here\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Extended XRN1 function to development, showing the 5'→3' decay pathway is required for epithelial morphogenesis.\",\n      \"evidence\": \"RNAi knockdown of xrn-1 in C. elegans embryos\",\n      \"pmids\": [\"14681585\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Target mRNAs driving the morphogenesis defect unknown\", \"RNAi-only evidence\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Identified XRN1 as the nuclease degrading the 3' products of RISC/siRNA-directed cleavage, integrating it into the RNAi pathway.\",\n      \"evidence\": \"RNAi depletion of XRN1 vs exosome in Drosophila S2 cells with intermediate detection\",\n      \"pmids\": [\"15703439\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Recruitment to RISC products not defined\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Showed XRN1 participates in rapid tRNA decay of hypomodified tRNAs, broadening its substrate range beyond mRNA.\",\n      \"evidence\": \"Genetic deletions in trm8Δ trm4Δ strains with tRNA stability and aminoacylation assays\",\n      \"pmids\": [\"18443146\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How hypomodified tRNAs become XRN1 substrates mechanistically unclear\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Established 5'-end RNA secondary structure as the molecular basis of XRN1 resistance using a narnavirus model.\",\n      \"evidence\": \"XRN1 overexpression/deletion and mutational analysis of viral 5' stem in yeast\",\n      \"pmids\": [\"18640978\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"High-resolution structure of the stalling element not determined here\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Defined the flaviviral xrRNA principle: a 3' UTR pseudoknot stalls XRN1 to generate sfRNA, the first defined RNA element that halts the processive enzyme.\",\n      \"evidence\": \"In vitro degradation with purified XRN1, structure probing, mutagenesis, and heterologous sfRNA production\",\n      \"pmids\": [\"20739539\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Atomic structure of stalled XRN1–xrRNA complex not resolved\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Solved the catalytic mechanism: structures revealed 5'-monophosphate recognition by a basic pocket and aromatic stacking driving processivity and coupled duplex melting.\",\n      \"evidence\": \"X-ray crystallography of Xrn1–substrate plus mutagenesis and processivity assays\",\n      \"pmids\": [\"21362555\", \"21297639\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Conformational dynamics during processive translocation not captured\", \"Partner-binding platform interactions inferred structurally but not all validated\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Showed viral host-shutoff (KSHV SOX) recruits XRN1 to translating mRNAs, linking endonucleolytic cleavage to XRN1 degradation during translation.\",\n      \"evidence\": \"Polysome sedimentation and XRN1 depletion with cleavage-intermediate detection\",\n      \"pmids\": [\"22046136\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct XRN1–ribosome contact not yet structurally shown at this stage\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Identified the direct decapping–decay coupling: an XRN1 DCP1-binding motif engages DCP1/EDC4 to hand off decapped mRNAs.\",\n      \"evidence\": \"Co-IP and NMR structure of DCP1 EVH1–XRN1 DBM in fly and human cells\",\n      \"pmids\": [\"23142987\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Stoichiometry and dynamics of the handoff in vivo not fully defined\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Established that flaviviral sfRNA represses XRN1 to globally stabilize host mRNAs during infection.\",\n      \"evidence\": \"sfRNA-null mutant virus with XRN1 activity and mRNA stability measurements\",\n      \"pmids\": [\"23006624\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Quantitative impact on specific host transcripts not delineated\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Showed miR-122 protects HCV RNA specifically from XRN1-mediated 5' decay, defining XRN1 as a major restriction nuclease antagonized by a host miRNA.\",\n      \"evidence\": \"siRNA knockdown, miR-122 supplementation, and decay-intermediate sequencing in infected cells\",\n      \"pmids\": [\"23248316\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism of miR-122 5'-end shielding not structurally defined\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Identified Dcs1 as an essential cofactor that activates Xrn1 by improving RNA affinity, required for respiratory growth.\",\n      \"evidence\": \"In vitro reconstitution with purified Xrn1/Dcs1, co-IP, and in vivo growth assays\",\n      \"pmids\": [\"22570495\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of Dcs1 activation not resolved\", \"Whether a mammalian equivalent exists not addressed\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Demonstrated Xrn1 is specifically required for the global mRNA buffering that couples decay rates to transcription, revealing a decay-to-synthesis feedback role.\",\n      \"evidence\": \"Comparative dynamic transcriptome analysis across 46 yeast decay mutants\",\n      \"pmids\": [\"24119399\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular signal transmitting decay status to transcription unknown\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Resolved the dengue xrRNA architecture, showing XRN1 stalls at a three-way-junction fold after processively degrading ~10 kb.\",\n      \"evidence\": \"Real-time in vitro XRN1 resistance assays, mutagenesis, and cell-based sfRNA detection\",\n      \"pmids\": [\"24692447\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Generality across all flaviviral xrRNAs not established here\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Defined XRN1 as a regulator of endogenous dsRNA and dsRNA-responsive innate immunity, since its depletion activates PKR and OAS/RNase L.\",\n      \"evidence\": \"siRNA depletion in vaccinia-infected cells with dsRNA and pathway activation assays\",\n      \"pmids\": [\"25766294\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Source of accumulating dsRNA not identified at this stage\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Revealed neuronal synaptic XRN1 bodies coupling XRN1 to activity-dependent local translational repression.\",\n      \"evidence\": \"Imaging in primary neurons with synaptic stimulation and XRN1 knockdown\",\n      \"pmids\": [\"25736288\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Target mRNAs and decay vs sequestration roles in SX-bodies unclear\", \"Single lab\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Connected Pacman/XRN1 to apoptosis by targeting pro-apoptotic hid and reaper mRNAs for degradation in Drosophila.\",\n      \"evidence\": \"Null mutant, rescue by pro-apoptotic gene deletion, and pre-mRNA/mRNA quantification\",\n      \"pmids\": [\"25836675\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether mammalian XRN1 regulates apoptotic transcripts similarly not addressed\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Showed glucose-regulated eisosome sequestration of Xrn1 inhibits its decay activity, defining a reversible spatial control mechanism.\",\n      \"evidence\": \"Live-cell imaging of GFP-Xrn1 with PIL1/SUR7 deletion and glucose addition\",\n      \"pmids\": [\"25811606\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Signal triggering eisosome recruitment not defined\", \"Single lab\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Mapped the Pat1–Xrn1 interaction via a helical leucine-rich motif shared with Dcp2, integrating Xrn1 into the decapping-activator network.\",\n      \"evidence\": \"Crystallography of Pat1–HLM, co-IP, and in vivo mRNA decay assays\",\n      \"pmids\": [\"29078363\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Competition between HLM partners in vivo not quantified\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Confirmed eisosome-sequestered Xrn1 is enzymatically intact and reactivated by glucose, establishing sequestration as a storage rather than degradation mechanism.\",\n      \"evidence\": \"mRNA decay assays in wild-type and pil1Δ strains with glucose addition\",\n      \"pmids\": [\"28501103\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Physiological advantage of sequestration not quantified\", \"Single lab\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Showed Xrn1 physically engages totivirus Gag and is under positive selection, defining a species-specific antiviral arms race.\",\n      \"evidence\": \"Co-IP of Xrn1–Gag, phylogenetic selection analysis, and cross-species complementation\",\n      \"pmids\": [\"27711183\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Functional consequence of Gag binding on Xrn1 activity unclear\", \"Single lab\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Extended XRN1-stalling RNA elements to bunyaviral/arenaviral structures, including a candidate G-quadruplex.\",\n      \"evidence\": \"In vitro XRN1 stalling assays with viral substrates and mutagenesis\",\n      \"pmids\": [\"29118186\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"G-quadruplex mechanism not confirmed structurally\", \"Single lab\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Implicated Xrn1 in telomere homeostasis, promoting checkpoint activation, Cdc13 loading, and Rif1 transcript downregulation.\",\n      \"evidence\": \"Genetic deletion with telomere length, checkpoint, ChIP, and RNA assays\",\n      \"pmids\": [\"28160602\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether telomere roles depend on RNA decay activity not fully separated\", \"Single lab\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Defined the YTHDC2–XRN1 interaction through ankyrin repeats, recruiting XRN1 to m6A-marked mRNAs for degradation.\",\n      \"evidence\": \"RNA-independent co-IP, domain mapping, and CRAC analysis\",\n      \"pmids\": [\"29970596\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In vivo extent of m6A-directed XRN1 decay not quantified\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Showed the DNA damage kinase Rad53 phosphorylates Xrn1, linking decay to checkpoint signaling, though intrinsic nuclease activity was unchanged in vitro.\",\n      \"evidence\": \"Phosphoproteomic screen and in vitro kinase plus nuclease assays\",\n      \"pmids\": [\"30377154\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"In vivo functional consequence of phosphorylation not established\", \"Phosphosites' effect on specificity untested\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Established XRN1 as a post-transcriptional negative regulator of autophagy via its ribonuclease activity in yeast and mammals.\",\n      \"evidence\": \"Chromosomal deletion, catalytic mutant analysis, and siRNA depletion with autophagy assays\",\n      \"pmids\": [\"29465287\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct ATG transcript targeting mechanism not fully defined\", \"Single lab\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Provided the structural basis for co-translational decay by visualizing Xrn1 docked at the ribosomal mRNA exit site ~17 nt from the decoding center.\",\n      \"evidence\": \"Cryo-EM of programmed 80S ribosome–Xrn1 complex\",\n      \"pmids\": [\"30911188\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How Xrn1 couples to ribosome speed/quality control not resolved\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Mapped the low-complexity CIR region of human XRN1 as a direct binder and inhibitor of CCR4-NOT and PatL1, coupling deadenylation to decay.\",\n      \"evidence\": \"In vitro deadenylase assays with purified proteins and reporter decay in XRN1-null complementation\",\n      \"pmids\": [\"31340047\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Physiological role of CIR-mediated deadenylase inhibition in vivo unclear\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Revealed a positive role for Xrn1 in translation and ER localization of a subset of membrane-protein mRNAs, coupling synthesis, translation, and decay.\",\n      \"evidence\": \"Ribosome profiling, polysome analysis, ER fractionation, and interaction studies\",\n      \"pmids\": [\"30899024\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism distinguishing stimulatory from degradative roles unclear\", \"Single lab\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Extended Xrn1's gene-expression coupling to transcription, showing it modulates Pol II initiation and elongation as an activator.\",\n      \"evidence\": \"NET-seq and transcription rate modeling in xrn1Δ yeast\",\n      \"pmids\": [\"32518159\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct mechanism connecting cytoplasmic Xrn1 to nuclear Pol II unknown\", \"Single lab\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Identified a separable deNADding activity by which Xrn1 removes intact NAD caps from RNAs, required for non-fermentative growth.\",\n      \"evidence\": \"In vitro NAD-cap decapping with a separation-of-function mutant and growth/mitochondrial RNA analysis\",\n      \"pmids\": [\"35173156\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether deNADding occurs in mammalian XRN1 not addressed here\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Showed measles virus relocalizes XRN1 to inclusion bodies to degrade dsRNA and suppress the PKR-ISR pathway, aiding replication.\",\n      \"evidence\": \"Immunofluorescence localization, XRN1 knockout, dsRNA and PKR phosphorylation assays\",\n      \"pmids\": [\"36300942\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism of XRN1 translocation to inclusion bodies unclear\", \"Single lab\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Showed influenza NS1 directly binds XRN1, which suppresses RIG-I-mediated IFN-β, defining a viral co-option of XRN1's immune-dampening role.\",\n      \"evidence\": \"Co-IP, co-localization, knockdown/overexpression, and IFN-β/p-IRF3 assays\",\n      \"pmids\": [\"34311580\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether NS1 alters XRN1 catalytic activity unclear\", \"Single lab\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Demonstrated XRN1 enhances the YTHDC2 3'→5' helicase activity essential for fertility, integrating XRN1 into germ-cell mitotic-to-meiotic transition control.\",\n      \"evidence\": \"In vitro helicase reconstitution with XRN1 plus mouse and zebrafish genetic models\",\n      \"pmids\": [\"35305312\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism by which XRN1 stimulates helicase activity unresolved\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Showed the EDC4–XRN1 interaction controls decapping flux and P-body homeostasis, with disruption stabilizing miRNA-targeted mRNAs and enlarging P-bodies.\",\n      \"evidence\": \"Interaction-disrupting mutants, reporter decay, P-body/stress-granule imaging, and null-cell complementation\",\n      \"pmids\": [\"37621215\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How XRN1 stoichiometry sets P-body size mechanistically unclear\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Established that XRN1 prevents accumulation of endogenous Alu-derived cytosolic dsRNA, defining XRN1 dependency in ISG-high cancers via PKR and RIG-I/MAVS.\",\n      \"evidence\": \"CRISPR deletion, dsRNA quantification, pathway epistasis, drug rescue, and pan-cancer screen analysis\",\n      \"pmids\": [\"38261511\", \"38261514\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Precise endogenous dsRNA species driving PKR vs MAVS not fully resolved\", \"Therapeutic window in tumors untested\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How XRN1's many context-specific roles—co-translational decay, decay-transcription buffering, deNADding, dsRNA surveillance, and partner-directed recruitment—are integrated and differentially regulated in human cells remains unresolved.\",\n      \"evidence\": \"No single study in the corpus reconciles XRN1's multiple activities under a unified regulatory framework\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No structure of the human ribosome–XRN1 complex\", \"Regulation of XRN1 partner choice (DCP1/EDC4 vs CCR4-NOT vs YTHDC2) in vivo not defined\", \"In vivo significance of Rad53 phosphorylation and mammalian cofactor equivalents of Dcs1 unknown\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140098\", \"supporting_discovery_ids\": [0, 1, 3, 10, 14, 15, 18, 44]},\n      {\"term_id\": \"GO:0016787\", \"supporting_discovery_ids\": [0, 18, 44]},\n      {\"term_id\": \"GO:0003723\", \"supporting_discovery_ids\": [10, 18, 24]},\n      {\"term_id\": \"GO:0003677\", \"supporting_discovery_ids\": [2, 4]},\n      {\"term_id\": \"GO:0008092\", \"supporting_discovery_ids\": [7]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [5, 11]},\n      {\"term_id\": \"GO:0005840\", \"supporting_discovery_ids\": [39]},\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [30, 43]},\n      {\"term_id\": \"GO:0005783\", \"supporting_discovery_ids\": [41]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-8953854\", \"supporting_discovery_ids\": [1, 14, 15, 21, 39, 40, 44]},\n      {\"term_id\": \"R-HSA-74160\", \"supporting_discovery_ids\": [25, 42]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [27, 46, 49, 50]},\n      {\"term_id\": \"R-HSA-9612973\", \"supporting_discovery_ids\": [38]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [22, 23, 45, 46, 49]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"DCP1\", \"EDC4\", \"PatL1/Pat1\", \"CCR4-NOT\", \"YTHDC2\", \"Dcs1\", \"NS1\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":8,"faith_total":9,"faith_pct":88.88888888888889}}