{"gene":"DDX21","run_date":"2026-06-09T23:54:41","timeline":{"discoveries":[{"year":2014,"finding":"DDX21 widely associates with Pol I- and Pol II-transcribed genes and diverse RNA species including rRNA, snoRNAs, and 7SK RNA. In the nucleolus, DDX21 directly contacts rRNA and snoRNAs to promote rRNA transcription, processing, and modification. In the nucleoplasm, DDX21 binds 7SK RNA as a component of the 7SK snRNP complex and is recruited to Pol II gene promoters where it facilitates P-TEFb release from 7SK snRNP in a helicase-activity-dependent manner, promoting transcription elongation of ribosomal protein and snoRNA genes.","method":"ChIP-seq, CLIP-seq, RNA immunoprecipitation, shRNA knockdown, helicase-dead mutant analysis, luciferase reporter assays","journal":"Nature","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — multiple orthogonal methods (ChIP-seq, CLIP-seq, RIP, mutant analysis) in a single rigorous study; helicase-activity dependence confirmed by mutagenesis","pmids":["25470060"],"is_preprint":false},{"year":2017,"finding":"The lncRNA SLERT interacts with DDX21 via a 143-nt non-snoRNA sequence. DDX21 forms ring-shaped structures (visualized by super-resolution microscopy) surrounding multiple Pol I complexes and suppresses pre-rRNA transcription. SLERT binding allosterically alters individual DDX21 molecules, loosens the DDX21 ring, and relieves DDX21-mediated suppression of Pol I transcription.","method":"Super-resolution imaging (STORM), RNA immunoprecipitation, CRISPR deletion, co-immunoprecipitation, in vitro binding assays","journal":"Cell","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — super-resolution structural characterization of DDX21 ring, multiple orthogonal methods confirming SLERT-DDX21 interaction and functional consequence on Pol I","pmids":["28475895"],"is_preprint":false},{"year":2019,"finding":"PARP-1 is activated by snoRNAs in the nucleolus and ADP-ribosylates DDX21. ADP-ribosylated DDX21 localizes to nucleoli and promotes rDNA transcription. Treatment with PARP inhibitors or mutation of the ADP-ribosylation sites on DDX21 reduces its nucleolar localization, rDNA transcription, ribosome biogenesis, protein translation, and cell growth.","method":"Co-immunoprecipitation, PARP inhibitor treatment, ADP-ribosylation site mutagenesis, RNA pol I transcription assays, xenograft models, immunofluorescence","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — mutagenesis of modification sites, in vitro and in vivo validation, multiple orthogonal methods across cell lines and xenografts","pmids":["31351877"],"is_preprint":false},{"year":2017,"finding":"DDX21 efficiently unwinds R-loops in vitro and in cells; depletion of DDX21 leads to accumulation of cellular R-loops and DNA double-strand breaks. DDX21 helicase activity is regulated by acetylation: CBP acetylates DDX21 to inhibit its activity, while SIRT7 deacetylates DDX21 to augment helicase activity and overcome R-loop-mediated stalling of RNA polymerases. DDX21 also resolves estrogen-induced R-loops on estrogen-responsive genes.","method":"In vitro R-loop unwinding assay, DRIP-seq (S9.6 antibody), co-immunoprecipitation, SIRT7/DDX21 knockdown, γH2AX measurement, acetylation/deacetylation assays","journal":"Genes & development","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — in vitro helicase assay plus mutagenesis context, genetic epistasis (SIRT7 and DDX21 double KD), multiple orthogonal methods in single rigorous study","pmids":["28790157"],"is_preprint":false},{"year":2011,"finding":"DDX21 forms a complex with DDX1, DHX36, and the adaptor TRIF in the cytosol of myeloid dendritic cells to sense dsRNA. DDX21 binds the TIR domain of TRIF via its PRK domain. Knockdown of DDX21 blocks type I IFN and cytokine responses to poly I:C, influenza A virus, and reovirus, establishing DDX21 as a component of a cytosolic dsRNA sensor that activates the TRIF pathway.","method":"Poly I:C affinity purification, mass spectrometry, shRNA knockdown, domain-mapping binding assays, IFN/cytokine reporter assays","journal":"Immunity","confidence":"High","confidence_rationale":"Tier 2 / Strong — biochemical isolation of complex, domain mapping, functional shRNA validation across multiple virus types","pmids":["21703541"],"is_preprint":false},{"year":2014,"finding":"DDX21 restricts influenza A virus by binding the viral polymerase subunit PB1 and inhibiting polymerase assembly, reducing viral RNA and protein synthesis. The viral NS1 protein overcomes this restriction by binding DDX21 and displacing PB1. Sequential interaction of PB1 and NS1 with DDX21 temporally regulates viral gene expression.","method":"Co-immunoprecipitation, shRNA knockdown, viral replication assays, NS1 mutant viruses with DDX21 knockdown rescue","journal":"Cell host & microbe","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal Co-IP, domain mapping, NS1 mutant virus with DDX21 KD rescue (genetic epistasis), replicated mechanistic steps","pmids":["24721576"],"is_preprint":false},{"year":2020,"finding":"Crystal structures of human DDX21 were determined in three states: apo, AMPPNP+ssRNA-bound (pre-hydrolysis), and ADP-bound (post-hydrolysis), revealing an open-to-closed conformational change upon RNA binding. The RNA unwinding machinery includes a wedge helix, sensor motif V, and the DEVD box linking ATP and RNA binding pockets. DDX21 unwinds dsRNA cooperatively (Hill coefficient analysis). The NS1 protein of influenza A inhibits DDX21 ATPase and unwinding activity via small RNAs that cooperatively assemble with DDX21 and NS1.","method":"X-ray crystallography, in vitro ATPase assay, RNA unwinding assay, site-directed mutagenesis (D339H/E340G), Hill coefficient analysis","journal":"Advanced science","confidence":"High","confidence_rationale":"Tier 1 / Strong — crystal structures in three functional states, in vitro biochemical assays, mutagenesis validation in single rigorous study","pmids":["32714761"],"is_preprint":false},{"year":2023,"finding":"Glucose binds the ATP-binding domain of DDX21, alters its conformation, inhibits helicase activity, and dissociates DDX21 dimers. During differentiation-associated intracellular glucose elevation, DDX21 re-localizes from the nucleolus to the nucleoplasm, assembles into larger complexes containing RNA splicing factors, and promotes splicing of pro-differentiation genes (GRHL3, KLF4, OVOL1, RBPJ) by binding a specific SCUGSDGC motif in mRNA introns.","method":"Azido-glucose click chemistry, in vitro helicase assay, SAXS, immunofluorescence, enhanced CLIP-seq, splicing assays, DDX21 knockdown/rescue","journal":"Cell","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — biochemical demonstration of glucose binding and conformational change, multiple orthogonal structural and functional methods, glucose-dependent re-localization tied to splicing function","pmids":["36608661"],"is_preprint":false},{"year":2024,"finding":"DDX21 recruits the m6A methyltransferase METTL3 to chromatin by recognizing co-transcriptionally formed R-loops, and DDX21's helicase activity is required for METTL3-mediated m6A deposition onto nascent RNA. At transcription termination regions, this DDX21-METTL3 nexus promotes XRN2-mediated RNAPII termination. Loss of DDX21 or its enzymatic activity leads to defective termination and DNA damage.","method":"Co-immunoprecipitation, ChIP-seq, m6A-seq (MeRIP), DRIP-seq, helicase-dead DDX21 mutant, XRN2 cleavage assays, γH2AX measurement","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — multiple orthogonal methods, mutagenesis of helicase activity, genomic and biochemical validation in single rigorous study","pmids":["38569554"],"is_preprint":false},{"year":2017,"finding":"DDX21 binds RNA G-quadruplexes (rG4s) directly and unwinds them. The C-terminus of DDX21 mediates quadruplex RNA binding. DDX21 recognizes the quadruplex topology with specificity involving 2'OH of loop nucleotides. DDX21 binding suppresses expression of a protein with G4s in the 3' UTR of its mRNA.","method":"Mass spectrometry pull-down from cell lysate, fluorescence binding assays, nuclease sensitivity assay, domain truncation mapping, mRNA reporter assay","journal":"Nucleic acids research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — biochemical validation of direct binding and unwinding, C-terminal domain mapped, functional readout; single lab","pmids":["28472472"],"is_preprint":false},{"year":2018,"finding":"The C-terminus of DDX21 directly binds TERRA (telomeric repeat-containing RNA) G-quadruplex. 2D saturation transfer difference NMR maps the binding site to the phosphoribose backbone of quadruplexes; specificity for TERRA is mediated by 2'OH of loop nucleotides.","method":"In vitro binding assays, 2D saturation transfer difference NMR, site-directed mutagenesis of 2'OH","journal":"Biochimica et biophysica acta. General subjects","confidence":"Medium","confidence_rationale":"Tier 1 / Weak — NMR-based epitope mapping with mutagenesis validation; single lab, no in-cell functional consequence measured","pmids":["29906500"],"is_preprint":false},{"year":2020,"finding":"DDX21 is dimeric, with a central dimerization domain identified by SAXS. Intact dimerization is essential for both ATP-dependent dsRNA unwinding and ATP-independent G-quadruplex remodeling activities in vitro. The Arg/Gly-rich C-terminus maintains high RNA affinity independent of dimerization.","method":"SAXS, in vitro helicase assays with dimerization-deficient mutants, G-quadruplex remodeling assays","journal":"iScience","confidence":"Medium","confidence_rationale":"Tier 1–2 / Moderate — SAXS structural analysis plus in vitro functional assays with mutants; single lab","pmids":["33313488"],"is_preprint":false},{"year":2014,"finding":"DDX21 is required for the association of late-acting snoRNPs (SNORD56, SNORD68) with pre-40S ribosomal complexes. DDX21 crosslinking sites on pre-rRNAs overlap with basepairing sites of these late snoRNAs. Earlier snoRNAs are unaffected by DDX21 depletion, establishing DDX21 as a regulator of the ordered hierarchy of snoRNP action in pre-40S maturation.","method":"CRAC (crosslinking and analysis of cDNAs), sucrose gradient sedimentation, shRNA knockdown, northern blotting","journal":"Nucleic acids research","confidence":"High","confidence_rationale":"Tier 2 / Strong — CRAC crosslinking maps DDX21 contact sites, overlapping with snoRNA basepairing sites; multiple snoRNAs tested with specificity controls","pmids":["25477391"],"is_preprint":false},{"year":2008,"finding":"c-Jun directly interacts with DDX21 and regulates its nucleolar localization. Depletion of c-Jun causes translocation of DDX21 from nucleolus to nucleoplasm, reduces DDX21 binding to rRNA, and inhibits 28S and 18S rRNA accumulation. Exogenous c-Jun rescues DDX21 nucleolar localization.","method":"siRNA knockdown, co-immunoprecipitation, RNA immunoprecipitation, indirect immunofluorescence, northern blotting","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — reciprocal Co-IP, rescue experiment, RNA binding assay; single lab with multiple orthogonal methods","pmids":["18180292"],"is_preprint":false},{"year":1997,"finding":"DDX21 (RH-II/Gu) is normally a nucleolar protein and undergoes reversible translocation from nucleolus to nucleoplasm upon treatment with cytotoxic drugs (actinomycin D, toyocamycin, mycophenolic acid), with the kinetics of reversibility depending on drug dose and type.","method":"Immunofluorescence, drug treatment and washout experiments in MCF-7 cells","journal":"Experimental cell research","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — direct localization experiments with functional drug perturbation; multiple drugs tested; single lab","pmids":["9299166"],"is_preprint":false},{"year":2014,"finding":"During dengue virus infection, DDX21 translocates from nucleus to cytoplasm to activate innate immune responses, thereby inhibiting DENV replication in early infection. DENV NS2B-NS3 protease complex subsequently degrades DDX21 to subvert innate immunity and facilitate replication.","method":"iTRAQ proteomics, LC-MS/MS, immunofluorescence, viral replication assays, protease inhibitor experiments","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 2–3 / Moderate — proteomic identification plus immunofluorescence localization plus viral replication readout; single lab","pmids":["27033607"],"is_preprint":false},{"year":2021,"finding":"Caspase-3 and caspase-6 cleave DDX21 at D126 upon virus infection or RNA/DNA ligand treatment. The resulting cytoplasmic cleaved DDX21 fragment negatively regulates IFN-β signaling by suppressing the formation of the DDX1-DDX21-DHX36 dsRNA-sensing complex.","method":"Co-immunoprecipitation, site-directed mutagenesis (D126 cleavage site), caspase inhibitor treatment, IFN-β reporter assay, immunofluorescence","journal":"mBio","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — cleavage site mutagenesis, caspase specificity determined, functional complex assembly assay; single lab with multiple methods","pmids":["34125604"],"is_preprint":false},{"year":2014,"finding":"DDX21 promotes rRNA processing in breast cancer cells and is required for phosphorylation of c-Jun on Ser73, thereby promoting AP-1 transcriptional activity. In nuclear (non-nucleolar) localized DDX21, these two functions operate independently.","method":"siRNA knockdown, immunofluorescence, rRNA processing assay (northern blot/pulse-chase), luciferase reporter for AP-1 activity, qRT-PCR, xenograft imaging","journal":"Breast cancer research : BCR","confidence":"Medium","confidence_rationale":"Tier 2–3 / Moderate — loss-of-function with two distinct mechanistic readouts; single lab","pmids":["25260534"],"is_preprint":false},{"year":2017,"finding":"In HIV-1 context: DDX21 binds the Rev Response Element (RRE) with high affinity, stimulating ATPase activity. DDX21 is both an ATP-dependent and ATP-independent helicase. Rev inhibits DDX21 ATPase and ATP-dependent helicase activities dose-dependently via a conserved DEAD-domain interaction involving Rev's nuclear diffusion inhibitory signal motif. DDX21 enhances Rev binding to the RRE.","method":"In vitro RNA binding assays, ATPase assay, helicase assay, pulldown, fluorescence anisotropy","journal":"Journal of molecular biology","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — in vitro biochemical reconstitution of binding and enzymatic activities; domain mapping; single lab","pmids":["28705764"],"is_preprint":false},{"year":1999,"finding":"Recombinant DDX21 (RH-II/Gu) expressed in a baculovirus system has RNA helicase activity on a 5'-tailed dsRNA substrate in vitro. Adriamycin inhibits DDX21 helicase activity (IC50 ~40 µM) by binding to the RNA substrate rather than directly to the protein.","method":"Baculovirus expression, in vitro helicase assay, RNA-drug binding assay (gel electrophoresis)","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 1 / Weak — in vitro reconstitution of helicase activity and mechanism of drug inhibition; single lab, single method","pmids":["10600508"],"is_preprint":false},{"year":2013,"finding":"WDR46 (nucleolar scaffold protein) is required for proper localization of DDX21 to the granular component of the nucleolus. Upon WDR46 knockdown, DDX21 mislocalizes to the edges of nucleoli, and proper DDX21 recruitment after cell division is impaired. WDR46 physically interacts with DDX21 via its intrinsically disordered N- and C-terminal regions.","method":"siRNA knockdown, immunofluorescence, co-immunoprecipitation, cell-cycle analysis","journal":"Genes to cells","confidence":"Medium","confidence_rationale":"Tier 2–3 / Moderate — direct localization experiment tied to protein interaction; single lab with Co-IP and imaging","pmids":["23848194"],"is_preprint":false},{"year":2012,"finding":"DDX21 (Gu/Ddx21) is a novel direct interactor of protein phosphatase PP1, identified by mitotic spindle enrichment and mass spectrometry. DDX21 is placed within the toposome (Topoisomerase IIα-containing complex) involved in mitotic chromatin regulation.","method":"Mitotic spindle biochemical enrichment, mass spectrometry, co-immunoprecipitation, in vitro binding assay","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — mass spectrometry identification plus Co-IP and direct binding; single lab; no functional mutagenesis","pmids":["22761809"],"is_preprint":false},{"year":2019,"finding":"At the ENPP2 locus, JMJD3 interacts with DDX21 (identified by mass spectrometry) and recruits DDX21 to the transcription start site and gene body. DDX21 resolves R-loops formed co-transcriptionally at ENPP2, enabling productive transcription. This JMJD3-DDX21 recruitment is controlled by a distant-acting enhancer.","method":"Mass spectrometry, co-immunoprecipitation, ChIP-qPCR, DRIP-qPCR (S9.6 antibody), CRISPR-Cas9 enhancer deletion","journal":"Nucleic acids research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal methods (Co-IP, ChIP, DRIP); single lab","pmids":["31251802"],"is_preprint":false},{"year":2024,"finding":"NAT10 acetyltransferase acetylates DDX21 at K236 and K573, enhancing DDX21 helicase activity to resolve nucleolar R-loops. Acetylation-mimicking DDX21 (2KQ) has increased helicase activity, and acetylation-deficient DDX21 (2KR) has decreased activity in vitro and in cells. NAT10 loss causes nucleolar R-loop accumulation and DNA damage, rescued by co-expression of acetylation-mimicking DDX21.","method":"Co-immunoprecipitation, GST pull-down, mass spectrometry for acetylation sites, in vitro helicase assay, immunofluorescence with RNase H control, CRISPR/shRNA knockdown, γH2AX measurement","journal":"Cell communication and signaling","confidence":"High","confidence_rationale":"Tier 1 / Strong — modification sites identified by MS, mutagenesis (2KQ/2KR) with in vitro helicase assay, genetic rescue in cells; multiple orthogonal methods","pmids":["39394182"],"is_preprint":false},{"year":2022,"finding":"NAT10 and DDX21 interact with RNase H1 (via BioID proximity labeling confirmed biochemically). Purified NAT10 and DDX21 proteins enhance RNase H1 cleavage rates in vitro. Reduction of either protein decreases PS-ASO activity and increases R-loop levels and impairs pre-rRNA processing.","method":"BioID proximity labeling, co-immunoprecipitation, in vitro RNase H1 cleavage assay, DRIP, knockdown, northern blotting","journal":"Nucleic acid therapeutics","confidence":"Medium","confidence_rationale":"Tier 1–2 / Moderate — in vitro reconstitution of enhanced RNase H1 activity, BioID plus biochemical confirmation; single lab","pmids":["35852833"],"is_preprint":false},{"year":2021,"finding":"In zebrafish, Ddx21 cell-autonomously regulates lymphatic vessel development by supporting Vegfc-Flt4-driven endothelial cell proliferation. Loss of Ddx21 reduces ribosome biogenesis, upregulates p53 and p21, and causes cell cycle arrest that blocks lymphangiogenesis.","method":"Zebrafish genetic screen, morpholino/mutant analysis, cell-autonomous transplantation experiments, immunofluorescence, ribosome biogenesis assays","journal":"Nature cell biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic loss-of-function with cell-autonomous transplant, pathway epistasis (p53/p21 upregulation); single study","pmids":["34750583"],"is_preprint":false},{"year":2020,"finding":"The phosphatase PRL3 binds DDX21 and restricts productive transcription elongation by RNAPII at MITF-regulated endolysosomal vesicle genes, controlling melanocyte stem cell differentiation. PRL3-DDX21 interaction limits transcriptional elongation as a differentiation checkpoint mechanism.","method":"Co-immunoprecipitation, ChIP-seq, RNAPII elongation assays, zebrafish genetic analysis, patient melanoma data","journal":"Developmental cell","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — reciprocal Co-IP and ChIP-seq functional readout; single lab with in vivo validation","pmids":["32652076"],"is_preprint":false},{"year":2020,"finding":"Nucleotide depletion (via DHODH inhibition with leflunomide) reduces DDX21 chromatin occupancy in melanoma cells. Progesterone receptor (Pgr) binds the RNA helicase Ddx21 (proteomics). DDX21 acts as a sensor and mediator of transcription during nucleotide stress, and ddx21-deficient zebrafish show resistance to leflunomide-induced neural crest defects.","method":"In vivo chemical suppressor screen (zebrafish), proteomics (Pgr-DDX21 interaction), ChIP-seq, nucleotide supplementation rescue","journal":"Nature cell biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vivo genetic evidence plus ChIP-seq; Pgr-DDX21 interaction by proteomics; single lab","pmids":["32231306"],"is_preprint":false},{"year":2018,"finding":"DDX21 suppresses Snail transcription independently of its helicase activity by recruiting PRC2 subunits SUZ12 and EZH2 to the Snail promoter, establishing a double-negative feedback loop where Snail also represses DDX21 transcription.","method":"ChIP assay, co-immunoprecipitation, overexpression/knockdown, luciferase reporter, in vivo metastasis assay","journal":"Cancer letters","confidence":"Medium","confidence_rationale":"Tier 2–3 / Moderate — ChIP showing DDX21 recruits PRC2 to Snail promoter; helicase-dead mutant confirms independence; single lab","pmids":["30165191"],"is_preprint":false},{"year":2019,"finding":"DDX21 regulates protein expression of MAGED2 through an rG4 structure in the MAGED2 5'-UTR. Cells expressing rG4-binding-deficient DDX21 (M4 mutant) show halved MAGED2 protein (but not mRNA) levels, leading to elevated TRAIL-R2 and TRAIL-mediated apoptosis sensitivity.","method":"Label-free proteomics, western blotting, qRT-PCR, rG4-binding-deficient DDX21 mutant expression, TRAIL apoptosis assay","journal":"RNA","confidence":"Medium","confidence_rationale":"Tier 2–3 / Moderate — rG4-binding-deficient mutant establishes G4-dependent translational regulation; single lab, proteomic discovery plus follow-up","pmids":["31653714"],"is_preprint":false},{"year":2022,"finding":"DDX21 interacts with WDR5 and recruits it to the CDK1 gene promoter, enhancing H3K4me3 trimethylation to activate CDK1 transcription in colorectal cancer cells. DDX21 knockdown reduces CDK1 expression and causes G2/M phase arrest.","method":"Co-immunoprecipitation, ChIP assay, gene expression profiling, knockdown experiments, cell cycle analysis","journal":"Journal of Cancer","confidence":"Medium","confidence_rationale":"Tier 2–3 / Moderate — Co-IP plus ChIP demonstrating recruitment and histone modification; single lab","pmids":["35371306"],"is_preprint":false},{"year":2022,"finding":"In the context of nuclear RNA activation (RNAa), CDK9 and DDX21 form a complex with nuclear AGO and TNRC6A. DDX21 inhibition suppresses RNAa by miR-34a and other miRNAs without inhibiting post-transcriptional regulation, placing DDX21 as necessary for release of paused RNAPII during RNAa.","method":"Co-immunoprecipitation, siRNA knockdown, Pol II ChIP, reporter assay distinguishing transcriptional vs. post-transcriptional regulation","journal":"Cell reports","confidence":"Medium","confidence_rationale":"Tier 2–3 / Moderate — complex identified by Co-IP, functional knockdown with mechanistic readout; single lab","pmids":["35417682"],"is_preprint":false},{"year":2021,"finding":"DDX21 interacts with AGO2 in the nucleus in an RNA-dependent indirect manner. DDX21 upregulates AGO2 protein levels and participates in AGO2-dependent alternative splicing of SMN2.","method":"Co-immunoprecipitation, GST pulldown, immunofluorescence, splicing assays","journal":"Bioscience, biotechnology, and biochemistry","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, indirect interaction, limited mechanistic follow-up","pmids":["33604619"],"is_preprint":false},{"year":2024,"finding":"DDX21 interacts with TERT to regulate rRNA transcription by affecting the binding of RNA Pol I to rDNA. BRAF mutation upregulates DDX21 expression through the MEK/ERK/GABP transcription factor axis (GABPA binds the DDX21 promoter). DDX21 knockdown suppresses multiple cancer hallmark gene expressions.","method":"Co-immunoprecipitation, mass spectrometry, ChIP-seq, Ribo-seq, RNA-seq, luciferase reporter assay, MAPK inhibitor treatment","journal":"Thyroid","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP identifies DDX21-TERT interaction, ChIP confirms GABPA binding to DDX21 promoter, multiple genomic approaches; single lab","pmids":["41817108"],"is_preprint":false},{"year":2024,"finding":"Calmodulin (CaM) interacts with nucleolar DDX21 in a Ca2+-dependent manner. CaM alters DDX21 conformation to liberate DDX21-sequestered RPA194 (the catalytic subunit of RNA Pol I), facilitating rDNA transcription. This CaM-DDX21 interaction couples activity-induced Ca2+ influx to nucleolar rRNA biogenesis in hippocampal neurons.","method":"Co-immunoprecipitation, fluorescence binding assay, Ca2+ chelation, conformation assay, small molecule screening, axon growth assay","journal":"The Journal of neuroscience","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP with Ca2+ dependence, conformational change assay, functional rescue; single lab","pmids":["39060175"],"is_preprint":false},{"year":2024,"finding":"U3 snoRNA is the predominant DDX21-binding partner during mitosis; DDX21 colocalizes with U3 snoRNA in the perichromosomal region (PR). U3 snoRNA regulates DDX21 PR localization by maintaining its mobility; DDX21 knockdown causes mitotic catastrophe similar to U3 snoRNA depletion. In vitro, Cy5-U3 snoRNA downsizes fibrous DDX21 condensates at proper molecular ratios.","method":"RIP, immunofluorescence, FRAP, DDX21 knockdown, U3 snoRNA depletion, in vitro condensate assay","journal":"Cell death & disease","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — RNA-protein interaction in mitotic context, localization tied to function, in vitro condensate reconstitution; single lab","pmids":["38760378"],"is_preprint":false},{"year":2023,"finding":"DDX21 undergoes phase separation in vitro and in CRC cells via its intrinsically disordered region (IDR). Phase-separated DDX21 binds the MCM5 gene locus; IDR mutations disrupting phase separation reduce MCM5 binding. MCM5 overexpression rescues the impaired metastatic ability of DDX21-depleted cells, placing MCM5 as a downstream target.","method":"In vitro phase separation assay, IDR mutagenesis, ChIP, knockdown/rescue experiments, in vivo metastasis model","journal":"Oncogene","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — phase separation reconstituted in vitro, IDR mutants used, genetic epistasis by rescue; single lab","pmids":["37029300"],"is_preprint":false},{"year":2023,"finding":"LINC00240 lncRNA stabilizes DDX21 protein by recruiting the deubiquitinase USP10, which removes ubiquitin from DDX21 and prevents its proteasomal degradation.","method":"Co-immunoprecipitation, ubiquitination assay, USP10 overexpression/knockdown, western blotting","journal":"Journal of experimental & clinical cancer research","confidence":"Medium","confidence_rationale":"Tier 2–3 / Moderate — Co-IP identifying lncRNA-DDX21-USP10 ternary stabilization; single lab","pmids":["37072811"],"is_preprint":false},{"year":2024,"finding":"TRIP13 (AAA+ ATPase) directly interacts with DDX21 and stabilizes it by restraining its ubiquitination degradation, promoting gastric cancer progression.","method":"Co-immunoprecipitation, ubiquitination assay, knockdown experiments, in vivo tumor model","journal":"Cell death & disease","confidence":"Low","confidence_rationale":"Tier 3 / Weak — Co-IP and ubiquitination assay; single lab, limited mechanistic depth","pmids":["39187490"],"is_preprint":false},{"year":2025,"finding":"DDX21 competitively binds SIRT7, relieving SIRT7-mediated inhibition of NAT10, thereby upregulating NAT10 expression and enhancing NAT10-mediated ac4C modification of ATAD2, SOX4, and SNX5 mRNAs in colorectal cancer.","method":"Co-immunoprecipitation, western blotting, MeRIP for ac4C, knockdown/overexpression, in vivo metastasis model","journal":"Cell death & disease","confidence":"Low","confidence_rationale":"Tier 3 / Weak — Co-IP showing competitive binding; ac4C modification measured; single lab, limited mechanistic resolution","pmids":["40301349"],"is_preprint":false},{"year":2025,"finding":"The small molecule KI-DX-014 (identified by small-molecule microarray against DDX21) inhibits DDX21-RNA interactions, reduces ATPase activity, modulates biomolecular condensate formation, and attenuates DDX21-dependent P-TEFb release from 7SK snRNP in vitro, suppressing RNAPII CTD phosphorylation.","method":"Small-molecule microarray, ATPase assay, condensate formation assay, in vitro 7SK snRNP P-TEFb release assay, zebrafish developmental assay","journal":"ACS chemical biology","confidence":"Medium","confidence_rationale":"Tier 1–2 / Moderate — in vitro biochemical reconstitution of multiple DDX21 functions inhibited by compound; single lab","pmids":["40637641"],"is_preprint":false},{"year":2021,"finding":"DDX21 inhibits FMDV IRES-dependent translation by binding FMDV IRES domains 2, 3, and 4. FMDV counteracts this by degrading DDX21 via its non-structural proteins 2B and 2C (through the caspase pathway) and 3Cpro (through the lysosomal pathway).","method":"Pulldown assay, dual-luciferase assay (IRES activity), knockdown/overexpression, confocal microscopy, pathway inhibitor experiments","journal":"Viruses","confidence":"Medium","confidence_rationale":"Tier 2–3 / Moderate — pulldown identifies IRES binding domains, IRES-luciferase assay is functional, degradation pathways distinguished; single lab","pmids":["34578346"],"is_preprint":false},{"year":2025,"finding":"HTLV-1 Gag interacts with DDX21 through zinc fingers in the NC domain, independently of RNA. DDX21 is packaged into virions. DDX21 alone enhances tRNAPro primer annealing to the HTLV-1 primer binding site, and DDX21 + RPL7 + Gag combination shows synergistic annealing activity.","method":"Affinity purification–mass spectrometry, reciprocal co-immunoprecipitation, domain-mapping, in vitro primer-annealing assays","journal":"bioRxiv (preprint)","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — reciprocal Co-IP with domain mapping, in vitro functional annealing assay; preprint, single lab","pmids":["40791341"],"is_preprint":true},{"year":2025,"finding":"Ddx21 interacts with the histone demethylase Kdm5a and co-occupies H3K4me3-marked active promoters. Loss of Ddx21 reduces H3K4me3 at rDNA and hematopoietic genes (cKit, Gata1). Kdm5a inhibition restores rRNA expression and translation in Ddx21-deficient fetal hematopoietic cells, demonstrating that Ddx21 sequesters Kdm5a to maintain active chromatin for ribosomal transcription.","method":"Conditional knockout, multi-omics (ChIP-seq, RNA-seq, ribosome profiling), co-immunoprecipitation, Kdm5a inhibitor rescue","journal":"bioRxiv (preprint)","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP, ChIP-seq, genetic rescue with Kdm5a inhibitor; preprint, single lab","pmids":["bio_10.1101_2025.09.04.674186"],"is_preprint":true}],"current_model":"DDX21 is a multifunctional nucleolar DEAD-box RNA helicase that coordinates ribosome biogenesis (promoting rRNA transcription, processing, and modification via direct rRNA/snoRNA contacts and nucleolar localization regulated by PARP1-mediated ADP-ribosylation, c-Jun, WDR46, and NAT10-mediated acetylation), controls RNA polymerase II elongation by releasing P-TEFb from 7SK snRNP in a helicase-dependent manner, resolves co-transcriptional R-loops and recruits the m6A methyltransferase METTL3 to promote transcription termination, unwinds RNA G-quadruplexes via its Arg/Gly-rich C-terminus, acts as a dimeric enzyme whose dimerization state regulates both ATPase-dependent and ATP-independent activities, senses transcriptional status and nucleotide availability through chromatin occupancy changes, functions as a cytosolic dsRNA sensor (within a DDX1-DDX21-DHX36-TRIF complex) to activate type I interferon responses, restricts multiple viruses by binding viral polymerase components or IRES elements while being counter-targeted by viral proteins (influenza NS1, DENV NS2B-NS3, FMDV 3Cpro, caspase-dependent cleavage), and responds to glucose by dissociating into monomers that relocalize to the nucleoplasm to regulate mRNA splicing during differentiation."},"narrative":{"mechanistic_narrative":"DDX21 is a nucleolar DEAD-box RNA helicase that integrates ribosome biogenesis with RNA polymerase activity by directly contacting rRNA, snoRNAs, and 7SK RNA: in the nucleolus it promotes rRNA transcription, processing, and modification, while in the nucleoplasm it binds 7SK snRNP at Pol II promoters and releases P-TEFb in a helicase-dependent manner to drive transcription elongation [PMID:25470060]. It enforces the ordered hierarchy of pre-40S maturation by recruiting late-acting snoRNPs to pre-rRNA at sites overlapping its own crosslinking footprint [PMID:25477391], and its activity over Pol I is gated by allosteric inputs—the lncRNA SLERT loosens ring-shaped DDX21 assemblies that otherwise suppress Pol I transcription [PMID:28475895], and U3 snoRNA tunes its mitotic perichromosomal localization and condensate size [PMID:38760378]. Crystal structures in apo, pre-hydrolysis, and post-hydrolysis states define an open-to-closed conformational cycle, and DDX21 unwinds dsRNA cooperatively as a dimer whose central dimerization domain is required for both ATP-dependent unwinding and ATP-independent G-quadruplex remodeling, the latter mediated by its Arg/Gly-rich C-terminus [PMID:32714761, PMID:33313488, PMID:28472472]. As a genome-stability factor, DDX21 unwinds R-loops to prevent double-strand breaks, and its helicase activity is set by reversible acetylation (CBP/SIRT7 and NAT10) [PMID:28790157, PMID:39394182]; at transcription termination regions it recruits METTL3 to deposit m6A on nascent RNA and promote XRN2-mediated RNAPII termination [PMID:38569554]. DDX21 localization and abundance are heavily regulated—by c-Jun, WDR46, PARP1-mediated ADP-ribosylation, glucose binding to its ATP pocket, and Ca2+/calmodulin—coupling rRNA biogenesis to cellular state and, upon glucose-driven dimer dissociation and nucleoplasmic relocalization, to mRNA splicing of pro-differentiation genes [PMID:18180292, PMID:23848194, PMID:31351877, PMID:36608661, PMID:39060175]. Beyond these nuclear roles, DDX21 acts in cytosolic innate immunity as part of a DDX1-DDX21-DHX36-TRIF dsRNA-sensing complex that activates type I interferon, and it restricts multiple viruses by engaging viral polymerase or IRES components, functions that diverse viral proteins counteract [PMID:21703541, PMID:24721576, PMID:34578346].","teleology":[{"year":1997,"claim":"Established that DDX21 is a nucleolar protein whose localization is dynamic, revealing that its nucleolar residence reports on transcriptional/metabolic state.","evidence":"Immunofluorescence with cytotoxic drug treatment and washout in MCF-7 cells","pmids":["9299166"],"confidence":"Medium","gaps":["No molecular function assigned","Mechanism of translocation unknown"]},{"year":1999,"claim":"First demonstrated DDX21 is a bona fide RNA helicase, defining its core enzymatic activity on tailed dsRNA substrates.","evidence":"Recombinant baculovirus-expressed protein in an in vitro helicase assay","pmids":["10600508"],"confidence":"Medium","gaps":["Single substrate type","No cellular substrate identified","Adriamycin inhibition acts via RNA, not protein"]},{"year":2008,"claim":"Identified c-Jun as a regulator of DDX21 nucleolar localization, linking an AP-1 transcription factor to rRNA accumulation.","evidence":"siRNA knockdown, reciprocal Co-IP, RIP, and rescue with immunofluorescence","pmids":["18180292"],"confidence":"Medium","gaps":["Single lab","Mechanism of c-Jun-directed retention unclear"]},{"year":2011,"claim":"Placed DDX21 in cytosolic innate immunity as part of a DDX1-DDX21-DHX36-TRIF complex sensing dsRNA, expanding its role beyond the nucleolus.","evidence":"Poly I:C affinity purification, mass spectrometry, domain mapping, shRNA knockdown across virus types in dendritic cells","pmids":["21703541"],"confidence":"High","gaps":["Stoichiometry of the sensing complex not resolved","How nucleolar DDX21 partitions to cytosol unclear"]},{"year":2014,"claim":"Defined DDX21's dual-compartment role in gene expression—nucleolar rRNA control and nucleoplasmic P-TEFb release from 7SK snRNP—and its ordered control of snoRNP-driven pre-40S maturation, establishing it as a master coordinator of ribosome biogenesis and Pol II elongation.","evidence":"ChIP-seq, CLIP-seq, RIP, helicase-dead mutants, reporters (Nature); CRAC crosslinking and gradient sedimentation (NAR)","pmids":["25470060","25477391"],"confidence":"High","gaps":["How DDX21 selects late vs early snoRNPs unknown","Helicase substrate specificity in vivo not fully mapped"]},{"year":2014,"claim":"Showed DDX21 restricts influenza A by binding polymerase subunit PB1, and that viral NS1 displaces PB1, defining a host-virus competition for DDX21.","evidence":"Reciprocal Co-IP, domain mapping, NS1 mutant virus with DDX21 knockdown rescue","pmids":["24721576"],"confidence":"High","gaps":["Whether helicase activity is needed for restriction not resolved"]},{"year":2017,"claim":"Identified DDX21 as an R-loop resolvase whose activity is set by acetylation (CBP/SIRT7), tying the helicase to genome stability and transcriptional throughput.","evidence":"In vitro R-loop unwinding, DRIP-seq, SIRT7/DDX21 double knockdown, acetylation assays, γH2AX","pmids":["28790157"],"confidence":"High","gaps":["Genome-wide R-loop targeting determinants incomplete","Acetylation site identity not yet mapped here"]},{"year":2017,"claim":"Revealed allosteric regulation of DDX21 by the lncRNA SLERT and visualized ring-shaped DDX21 assemblies suppressing Pol I, showing RNA partners gate its enzymatic state.","evidence":"STORM super-resolution imaging, RIP, CRISPR deletion, in vitro binding","pmids":["28475895"],"confidence":"High","gaps":["Molecular basis of ring formation unresolved","How SLERT binding propagates to ATPase cycle unclear"]},{"year":2017,"claim":"Established the Arg/Gly-rich C-terminus as a direct RNA G-quadruplex binder/unwinder, defining a structure-specific RNA recognition activity distinct from canonical duplex unwinding.","evidence":"MS pull-down, fluorescence binding, nuclease sensitivity, domain truncation, mRNA reporter","pmids":["28472472"],"confidence":"Medium","gaps":["Single lab","Cellular scope of rG4 targets limited"]},{"year":2018,"claim":"Mapped the C-terminal G-quadruplex epitope at residue resolution on TERRA, refining the structural basis of quadruplex specificity.","evidence":"In vitro binding and 2D STD NMR with 2'OH mutagenesis","pmids":["29906500"],"confidence":"Medium","gaps":["No in-cell functional consequence measured","Single lab"]},{"year":2019,"claim":"Connected nucleolar PARP1/snoRNA signaling to DDX21 via ADP-ribosylation, providing a post-translational switch for its nucleolar retention and rDNA transcription.","evidence":"Co-IP, PARP inhibitors, ADP-ribosylation site mutagenesis, Pol I assays, xenografts","pmids":["31351877"],"confidence":"High","gaps":["ADP-ribosylation site residues' structural effect unclear","Crosstalk with acetylation not addressed"]},{"year":2020,"claim":"Provided three-state crystal structures and dimerization analysis, defining the conformational cycle and showing dimerization is required for both ATP-dependent and ATP-independent activities.","evidence":"X-ray crystallography (apo/AMPPNP-ssRNA/ADP), ATPase and unwinding assays, mutagenesis (Advanced Science); SAXS with dimerization mutants (iScience)","pmids":["32714761","33313488"],"confidence":"Medium","gaps":["Full-length structure including IDR/C-terminus not resolved","Dimer architecture from SAXS only"]},{"year":2023,"claim":"Showed glucose directly binds the ATP-binding domain to dissociate DDX21 dimers and trigger nucleoplasmic relocalization toward mRNA splicing, linking metabolic state to a function switch during differentiation.","evidence":"Azido-glucose click chemistry, in vitro helicase, SAXS, eCLIP, splicing assays, knockdown/rescue","pmids":["36608661"],"confidence":"High","gaps":["Generality of the SCUGSDGC splicing motif across cell types unknown","How monomers recruit splicing factors mechanistically unclear"]},{"year":2024,"claim":"Defined a DDX21-METTL3 nexus that couples R-loop recognition and m6A deposition to XRN2-mediated RNAPII termination, integrating DDX21 helicase activity with transcription termination and genome integrity.","evidence":"Co-IP, ChIP-seq, MeRIP, DRIP-seq, helicase-dead mutant, XRN2 cleavage assays, γH2AX","pmids":["38569554"],"confidence":"High","gaps":["Order of R-loop resolution vs m6A deposition not fully resolved","Direct DDX21-METTL3 interface unmapped"]},{"year":2024,"claim":"Identified NAT10 acetylation of DDX21 at K236/K573 as an activating modification for R-loop resolution, and showed DDX21/NAT10 enhance RNase H1 activity, embedding DDX21 in a modification-controlled R-loop clearance network.","evidence":"MS acetylation mapping, 2KQ/2KR mutants, in vitro helicase, genetic rescue, γH2AX; BioID and in vitro RNase H1 cleavage assays","pmids":["39394182","35852833"],"confidence":"High","gaps":["Interplay of NAT10 acetylation with SIRT7/CBP acetylation not integrated","RNase H1 enhancement mechanism structurally undefined"]},{"year":2024,"claim":"Showed Ca2+/calmodulin alters DDX21 conformation to liberate sequestered RPA194 and drive rDNA transcription, coupling neuronal activity-induced calcium signaling to nucleolar biogenesis.","evidence":"Co-IP with Ca2+ dependence, conformation assays, small-molecule screen, axon growth assay in hippocampal neurons","pmids":["39060175"],"confidence":"Medium","gaps":["Single lab","Generalizability beyond neurons untested"]},{"year":2024,"claim":"Demonstrated U3 snoRNA controls mitotic DDX21 perichromosomal localization and condensate behavior, extending DDX21 RNA-dependent regulation into cell division.","evidence":"RIP, immunofluorescence, FRAP, knockdown/depletion, in vitro condensate assay","pmids":["38760378"],"confidence":"Medium","gaps":["Functional consequence of perichromosomal DDX21 not fully defined","Single lab"]},{"year":2025,"claim":"Identified a selective small-molecule inhibitor (KI-DX-014) that blocks DDX21-RNA binding, ATPase, condensate formation, and 7SK-P-TEFb release, providing a chemical tool validating multiple DDX21 functions.","evidence":"Small-molecule microarray, ATPase and condensate assays, in vitro 7SK P-TEFb release, zebrafish developmental assay","pmids":["40637641"],"confidence":"Medium","gaps":["Selectivity over other helicases not exhaustively profiled","In vivo efficacy limited to zebrafish readout"]},{"year":null,"claim":"How the many regulatory inputs (ADP-ribosylation, acetylation, glucose, Ca2+/CaM, dimerization, phase separation, and partner RNAs) are integrated to dynamically partition DDX21 among ribosome biogenesis, transcription elongation/termination, splicing, and immune sensing remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No unified model of compartment-switching control","Crosstalk between PTMs not co-assayed","Full-length structure with IDR and bound regulators lacking"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140098","term_label":"catalytic activity, acting on RNA","supporting_discovery_ids":[0,3,6,8,9,19]},{"term_id":"GO:0003723","term_label":"RNA binding","supporting_discovery_ids":[0,9,10,12,18,35]},{"term_id":"GO:0140657","term_label":"ATP-dependent activity","supporting_discovery_ids":[6,11,18,40]},{"term_id":"GO:0140299","term_label":"molecular sensor activity","supporting_discovery_ids":[4,7,27]}],"localization":[{"term_id":"GO:0005730","term_label":"nucleolus","supporting_discovery_ids":[0,1,2,13,14,20,34]},{"term_id":"GO:0005654","term_label":"nucleoplasm","supporting_discovery_ids":[0,7,13,14,17]},{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[4,15,16]},{"term_id":"GO:0000228","term_label":"nuclear chromosome","supporting_discovery_ids":[35]}],"pathway":[{"term_id":"R-HSA-74160","term_label":"Gene expression (Transcription)","supporting_discovery_ids":[0,8,22,26,31]},{"term_id":"R-HSA-8953854","term_label":"Metabolism of RNA","supporting_discovery_ids":[0,7,12]},{"term_id":"R-HSA-1852241","term_label":"Organelle biogenesis and maintenance","supporting_discovery_ids":[1,2,12,25]},{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[4,5,16]},{"term_id":"R-HSA-73894","term_label":"DNA Repair","supporting_discovery_ids":[3,8,23]}],"complexes":["7SK snRNP","DDX1-DDX21-DHX36-TRIF dsRNA-sensing complex"],"partners":["METTL3","TRIF","WDR46","SIRT7","NAT10","PARP1","DDX1","DHX36"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q9NY93","full_name":"Probable ATP-dependent RNA helicase DDX56","aliases":["ATP-dependent 61 kDa nucleolar RNA helicase","DEAD box protein 21","DEAD box protein 56"],"length_aa":547,"mass_kda":61.6,"function":"Nucleolar RNA helicase that plays a role in various biological processes including innate immunity, ribosome biogenesis or nucleolus organization (PubMed:31340999, PubMed:33789112). Plays an essential role in maintaining nucleolar integrity in planarian stem cells (PubMed:33789112). Maintains embryonic stem cells proliferation by conventional regulation of ribosome assembly and interaction with OCT4 and POU5F1 complex (By similarity). Regulates antiviral innate immunity by inhibiting the virus-triggered signaling nuclear translocation of IRF3 (PubMed:31340999). Mechanistically, acts by disrupting the interaction between IRF3 and importin IPO5 (PubMed:31340999). May play a role in later stages of the processing of the pre-ribosomal particles leading to mature 60S ribosomal subunits. Has intrinsic ATPase activity (Microbial infection) Helicase activity is important for packaging viral RNA into virions during West Nile virus infection (Microbial infection) Plays a positive role in foot-and-mouth disease virus replication by inhibiting the phosphorylation of IRF3 leading to inhibition of type I interferon (Microbial infection) Plays a positive role in EMCV replication by interrupting IRF3 phosphorylation and its nucleus translocation","subcellular_location":"Nucleus, nucleolus","url":"https://www.uniprot.org/uniprotkb/Q9NY93/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":true,"resolved_as":"","url":"https://depmap.org/portal/gene/DDX21","classification":"Common Essential","n_dependent_lines":1175,"n_total_lines":1208,"dependency_fraction":0.972682119205298},"opencell":{"profiled":true,"resolved_as":"","ensg_id":"ENSG00000165732","cell_line_id":"CID001051","localizations":[{"compartment":"nucleolus_gc","grade":3}],"interactors":[{"gene":"C1QBP","stoichiometry":10.0},{"gene":"RPS28","stoichiometry":10.0},{"gene":"RPL27","stoichiometry":10.0},{"gene":"YBX1","stoichiometry":10.0},{"gene":"HNRNPA1;HNRNPA1L2","stoichiometry":10.0},{"gene":"RPL13","stoichiometry":10.0},{"gene":"RBMX;RBMXL2","stoichiometry":10.0},{"gene":"HNRNPAB","stoichiometry":10.0},{"gene":"HNRNPA2B1","stoichiometry":10.0},{"gene":"HNRNPA3","stoichiometry":10.0}],"url":"https://opencell.sf.czbiohub.org/target/CID001051","total_profiled":1310},"omim":[{"mim_id":"620106","title":"SPASTIC PARAPLEGIA 88, AUTOSOMAL DOMINANT; SPG88","url":"https://www.omim.org/entry/620106"},{"mim_id":"619520","title":"BOX H/ACA SMALL NUCLEOLAR RNA-ENDED LONG NONCODING RNA THAT ENHANCES PRE-rRNA TRANSCRIPTION; SLERT","url":"https://www.omim.org/entry/619520"},{"mim_id":"612767","title":"DEAH-BOX HELICASE 36; DHX36","url":"https://www.omim.org/entry/612767"},{"mim_id":"610373","title":"DExD-BOX HELICASE 50; DDX50","url":"https://www.omim.org/entry/610373"},{"mim_id":"607601","title":"TIR DOMAIN-CONTAINING ADAPTOR MOLECULE 1; TICAM1","url":"https://www.omim.org/entry/607601"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Enhanced","locations":[{"location":"Nucleoli rim","reliability":"Enhanced"},{"location":"Mitotic chromosome","reliability":"Enhanced"},{"location":"Nucleoplasm","reliability":"Additional"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/DDX21"},"hgnc":{"alias_symbol":["RH-II/GU","GURDB","Gu-alpha"],"prev_symbol":[]},"alphafold":{"accession":"Q9NY93","domains":[{"cath_id":"3.40.50.300","chopping":"8-70_77-218","consensus_level":"high","plddt":87.59,"start":8,"end":218},{"cath_id":"3.40.50.300","chopping":"230-321_345-437_483-500","consensus_level":"high","plddt":83.72,"start":230,"end":500}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9NY93","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q9NY93-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q9NY93-F1-predicted_aligned_error_v6.png","plddt_mean":79.81},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=DDX21","jax_strain_url":"https://www.jax.org/strain/search?query=DDX21"},"sequence":{"accession":"Q9NY93","fasta_url":"https://rest.uniprot.org/uniprotkb/Q9NY93.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q9NY93/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9NY93"}},"corpus_meta":[{"pmid":"21703541","id":"PMC_21703541","title":"DDX1, DDX21, and DHX36 helicases form a complex with the adaptor molecule TRIF to sense dsRNA in dendritic cells.","date":"2011","source":"Immunity","url":"https://pubmed.ncbi.nlm.nih.gov/21703541","citation_count":306,"is_preprint":false},{"pmid":"25470060","id":"PMC_25470060","title":"RNA helicase DDX21 coordinates transcription and ribosomal RNA processing.","date":"2014","source":"Nature","url":"https://pubmed.ncbi.nlm.nih.gov/25470060","citation_count":266,"is_preprint":false},{"pmid":"28475895","id":"PMC_28475895","title":"SLERT Regulates DDX21 Rings Associated with Pol I Transcription.","date":"2017","source":"Cell","url":"https://pubmed.ncbi.nlm.nih.gov/28475895","citation_count":238,"is_preprint":false},{"pmid":"31351877","id":"PMC_31351877","title":"Activation of PARP-1 by snoRNAs Controls Ribosome Biogenesis and Cell Growth via the RNA Helicase DDX21.","date":"2019","source":"Molecular 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In the nucleolus, DDX21 directly contacts rRNA and snoRNAs to promote rRNA transcription, processing, and modification. In the nucleoplasm, DDX21 binds 7SK RNA as a component of the 7SK snRNP complex and is recruited to Pol II gene promoters where it facilitates P-TEFb release from 7SK snRNP in a helicase-activity-dependent manner, promoting transcription elongation of ribosomal protein and snoRNA genes.\",\n      \"method\": \"ChIP-seq, CLIP-seq, RNA immunoprecipitation, shRNA knockdown, helicase-dead mutant analysis, luciferase reporter assays\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — multiple orthogonal methods (ChIP-seq, CLIP-seq, RIP, mutant analysis) in a single rigorous study; helicase-activity dependence confirmed by mutagenesis\",\n      \"pmids\": [\"25470060\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"The lncRNA SLERT interacts with DDX21 via a 143-nt non-snoRNA sequence. DDX21 forms ring-shaped structures (visualized by super-resolution microscopy) surrounding multiple Pol I complexes and suppresses pre-rRNA transcription. SLERT binding allosterically alters individual DDX21 molecules, loosens the DDX21 ring, and relieves DDX21-mediated suppression of Pol I transcription.\",\n      \"method\": \"Super-resolution imaging (STORM), RNA immunoprecipitation, CRISPR deletion, co-immunoprecipitation, in vitro binding assays\",\n      \"journal\": \"Cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — super-resolution structural characterization of DDX21 ring, multiple orthogonal methods confirming SLERT-DDX21 interaction and functional consequence on Pol I\",\n      \"pmids\": [\"28475895\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"PARP-1 is activated by snoRNAs in the nucleolus and ADP-ribosylates DDX21. ADP-ribosylated DDX21 localizes to nucleoli and promotes rDNA transcription. Treatment with PARP inhibitors or mutation of the ADP-ribosylation sites on DDX21 reduces its nucleolar localization, rDNA transcription, ribosome biogenesis, protein translation, and cell growth.\",\n      \"method\": \"Co-immunoprecipitation, PARP inhibitor treatment, ADP-ribosylation site mutagenesis, RNA pol I transcription assays, xenograft models, immunofluorescence\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — mutagenesis of modification sites, in vitro and in vivo validation, multiple orthogonal methods across cell lines and xenografts\",\n      \"pmids\": [\"31351877\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"DDX21 efficiently unwinds R-loops in vitro and in cells; depletion of DDX21 leads to accumulation of cellular R-loops and DNA double-strand breaks. DDX21 helicase activity is regulated by acetylation: CBP acetylates DDX21 to inhibit its activity, while SIRT7 deacetylates DDX21 to augment helicase activity and overcome R-loop-mediated stalling of RNA polymerases. DDX21 also resolves estrogen-induced R-loops on estrogen-responsive genes.\",\n      \"method\": \"In vitro R-loop unwinding assay, DRIP-seq (S9.6 antibody), co-immunoprecipitation, SIRT7/DDX21 knockdown, γH2AX measurement, acetylation/deacetylation assays\",\n      \"journal\": \"Genes & development\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — in vitro helicase assay plus mutagenesis context, genetic epistasis (SIRT7 and DDX21 double KD), multiple orthogonal methods in single rigorous study\",\n      \"pmids\": [\"28790157\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"DDX21 forms a complex with DDX1, DHX36, and the adaptor TRIF in the cytosol of myeloid dendritic cells to sense dsRNA. DDX21 binds the TIR domain of TRIF via its PRK domain. Knockdown of DDX21 blocks type I IFN and cytokine responses to poly I:C, influenza A virus, and reovirus, establishing DDX21 as a component of a cytosolic dsRNA sensor that activates the TRIF pathway.\",\n      \"method\": \"Poly I:C affinity purification, mass spectrometry, shRNA knockdown, domain-mapping binding assays, IFN/cytokine reporter assays\",\n      \"journal\": \"Immunity\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — biochemical isolation of complex, domain mapping, functional shRNA validation across multiple virus types\",\n      \"pmids\": [\"21703541\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"DDX21 restricts influenza A virus by binding the viral polymerase subunit PB1 and inhibiting polymerase assembly, reducing viral RNA and protein synthesis. The viral NS1 protein overcomes this restriction by binding DDX21 and displacing PB1. Sequential interaction of PB1 and NS1 with DDX21 temporally regulates viral gene expression.\",\n      \"method\": \"Co-immunoprecipitation, shRNA knockdown, viral replication assays, NS1 mutant viruses with DDX21 knockdown rescue\",\n      \"journal\": \"Cell host & microbe\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal Co-IP, domain mapping, NS1 mutant virus with DDX21 KD rescue (genetic epistasis), replicated mechanistic steps\",\n      \"pmids\": [\"24721576\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Crystal structures of human DDX21 were determined in three states: apo, AMPPNP+ssRNA-bound (pre-hydrolysis), and ADP-bound (post-hydrolysis), revealing an open-to-closed conformational change upon RNA binding. The RNA unwinding machinery includes a wedge helix, sensor motif V, and the DEVD box linking ATP and RNA binding pockets. DDX21 unwinds dsRNA cooperatively (Hill coefficient analysis). The NS1 protein of influenza A inhibits DDX21 ATPase and unwinding activity via small RNAs that cooperatively assemble with DDX21 and NS1.\",\n      \"method\": \"X-ray crystallography, in vitro ATPase assay, RNA unwinding assay, site-directed mutagenesis (D339H/E340G), Hill coefficient analysis\",\n      \"journal\": \"Advanced science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — crystal structures in three functional states, in vitro biochemical assays, mutagenesis validation in single rigorous study\",\n      \"pmids\": [\"32714761\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Glucose binds the ATP-binding domain of DDX21, alters its conformation, inhibits helicase activity, and dissociates DDX21 dimers. During differentiation-associated intracellular glucose elevation, DDX21 re-localizes from the nucleolus to the nucleoplasm, assembles into larger complexes containing RNA splicing factors, and promotes splicing of pro-differentiation genes (GRHL3, KLF4, OVOL1, RBPJ) by binding a specific SCUGSDGC motif in mRNA introns.\",\n      \"method\": \"Azido-glucose click chemistry, in vitro helicase assay, SAXS, immunofluorescence, enhanced CLIP-seq, splicing assays, DDX21 knockdown/rescue\",\n      \"journal\": \"Cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — biochemical demonstration of glucose binding and conformational change, multiple orthogonal structural and functional methods, glucose-dependent re-localization tied to splicing function\",\n      \"pmids\": [\"36608661\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"DDX21 recruits the m6A methyltransferase METTL3 to chromatin by recognizing co-transcriptionally formed R-loops, and DDX21's helicase activity is required for METTL3-mediated m6A deposition onto nascent RNA. At transcription termination regions, this DDX21-METTL3 nexus promotes XRN2-mediated RNAPII termination. Loss of DDX21 or its enzymatic activity leads to defective termination and DNA damage.\",\n      \"method\": \"Co-immunoprecipitation, ChIP-seq, m6A-seq (MeRIP), DRIP-seq, helicase-dead DDX21 mutant, XRN2 cleavage assays, γH2AX measurement\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — multiple orthogonal methods, mutagenesis of helicase activity, genomic and biochemical validation in single rigorous study\",\n      \"pmids\": [\"38569554\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"DDX21 binds RNA G-quadruplexes (rG4s) directly and unwinds them. The C-terminus of DDX21 mediates quadruplex RNA binding. DDX21 recognizes the quadruplex topology with specificity involving 2'OH of loop nucleotides. DDX21 binding suppresses expression of a protein with G4s in the 3' UTR of its mRNA.\",\n      \"method\": \"Mass spectrometry pull-down from cell lysate, fluorescence binding assays, nuclease sensitivity assay, domain truncation mapping, mRNA reporter assay\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — biochemical validation of direct binding and unwinding, C-terminal domain mapped, functional readout; single lab\",\n      \"pmids\": [\"28472472\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"The C-terminus of DDX21 directly binds TERRA (telomeric repeat-containing RNA) G-quadruplex. 2D saturation transfer difference NMR maps the binding site to the phosphoribose backbone of quadruplexes; specificity for TERRA is mediated by 2'OH of loop nucleotides.\",\n      \"method\": \"In vitro binding assays, 2D saturation transfer difference NMR, site-directed mutagenesis of 2'OH\",\n      \"journal\": \"Biochimica et biophysica acta. General subjects\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Weak — NMR-based epitope mapping with mutagenesis validation; single lab, no in-cell functional consequence measured\",\n      \"pmids\": [\"29906500\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"DDX21 is dimeric, with a central dimerization domain identified by SAXS. Intact dimerization is essential for both ATP-dependent dsRNA unwinding and ATP-independent G-quadruplex remodeling activities in vitro. The Arg/Gly-rich C-terminus maintains high RNA affinity independent of dimerization.\",\n      \"method\": \"SAXS, in vitro helicase assays with dimerization-deficient mutants, G-quadruplex remodeling assays\",\n      \"journal\": \"iScience\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1–2 / Moderate — SAXS structural analysis plus in vitro functional assays with mutants; single lab\",\n      \"pmids\": [\"33313488\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"DDX21 is required for the association of late-acting snoRNPs (SNORD56, SNORD68) with pre-40S ribosomal complexes. DDX21 crosslinking sites on pre-rRNAs overlap with basepairing sites of these late snoRNAs. Earlier snoRNAs are unaffected by DDX21 depletion, establishing DDX21 as a regulator of the ordered hierarchy of snoRNP action in pre-40S maturation.\",\n      \"method\": \"CRAC (crosslinking and analysis of cDNAs), sucrose gradient sedimentation, shRNA knockdown, northern blotting\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — CRAC crosslinking maps DDX21 contact sites, overlapping with snoRNA basepairing sites; multiple snoRNAs tested with specificity controls\",\n      \"pmids\": [\"25477391\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"c-Jun directly interacts with DDX21 and regulates its nucleolar localization. Depletion of c-Jun causes translocation of DDX21 from nucleolus to nucleoplasm, reduces DDX21 binding to rRNA, and inhibits 28S and 18S rRNA accumulation. Exogenous c-Jun rescues DDX21 nucleolar localization.\",\n      \"method\": \"siRNA knockdown, co-immunoprecipitation, RNA immunoprecipitation, indirect immunofluorescence, northern blotting\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal Co-IP, rescue experiment, RNA binding assay; single lab with multiple orthogonal methods\",\n      \"pmids\": [\"18180292\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"DDX21 (RH-II/Gu) is normally a nucleolar protein and undergoes reversible translocation from nucleolus to nucleoplasm upon treatment with cytotoxic drugs (actinomycin D, toyocamycin, mycophenolic acid), with the kinetics of reversibility depending on drug dose and type.\",\n      \"method\": \"Immunofluorescence, drug treatment and washout experiments in MCF-7 cells\",\n      \"journal\": \"Experimental cell research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — direct localization experiments with functional drug perturbation; multiple drugs tested; single lab\",\n      \"pmids\": [\"9299166\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"During dengue virus infection, DDX21 translocates from nucleus to cytoplasm to activate innate immune responses, thereby inhibiting DENV replication in early infection. DENV NS2B-NS3 protease complex subsequently degrades DDX21 to subvert innate immunity and facilitate replication.\",\n      \"method\": \"iTRAQ proteomics, LC-MS/MS, immunofluorescence, viral replication assays, protease inhibitor experiments\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 / Moderate — proteomic identification plus immunofluorescence localization plus viral replication readout; single lab\",\n      \"pmids\": [\"27033607\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Caspase-3 and caspase-6 cleave DDX21 at D126 upon virus infection or RNA/DNA ligand treatment. The resulting cytoplasmic cleaved DDX21 fragment negatively regulates IFN-β signaling by suppressing the formation of the DDX1-DDX21-DHX36 dsRNA-sensing complex.\",\n      \"method\": \"Co-immunoprecipitation, site-directed mutagenesis (D126 cleavage site), caspase inhibitor treatment, IFN-β reporter assay, immunofluorescence\",\n      \"journal\": \"mBio\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — cleavage site mutagenesis, caspase specificity determined, functional complex assembly assay; single lab with multiple methods\",\n      \"pmids\": [\"34125604\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"DDX21 promotes rRNA processing in breast cancer cells and is required for phosphorylation of c-Jun on Ser73, thereby promoting AP-1 transcriptional activity. In nuclear (non-nucleolar) localized DDX21, these two functions operate independently.\",\n      \"method\": \"siRNA knockdown, immunofluorescence, rRNA processing assay (northern blot/pulse-chase), luciferase reporter for AP-1 activity, qRT-PCR, xenograft imaging\",\n      \"journal\": \"Breast cancer research : BCR\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 / Moderate — loss-of-function with two distinct mechanistic readouts; single lab\",\n      \"pmids\": [\"25260534\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"In HIV-1 context: DDX21 binds the Rev Response Element (RRE) with high affinity, stimulating ATPase activity. DDX21 is both an ATP-dependent and ATP-independent helicase. Rev inhibits DDX21 ATPase and ATP-dependent helicase activities dose-dependently via a conserved DEAD-domain interaction involving Rev's nuclear diffusion inhibitory signal motif. DDX21 enhances Rev binding to the RRE.\",\n      \"method\": \"In vitro RNA binding assays, ATPase assay, helicase assay, pulldown, fluorescence anisotropy\",\n      \"journal\": \"Journal of molecular biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro biochemical reconstitution of binding and enzymatic activities; domain mapping; single lab\",\n      \"pmids\": [\"28705764\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"Recombinant DDX21 (RH-II/Gu) expressed in a baculovirus system has RNA helicase activity on a 5'-tailed dsRNA substrate in vitro. Adriamycin inhibits DDX21 helicase activity (IC50 ~40 µM) by binding to the RNA substrate rather than directly to the protein.\",\n      \"method\": \"Baculovirus expression, in vitro helicase assay, RNA-drug binding assay (gel electrophoresis)\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Weak — in vitro reconstitution of helicase activity and mechanism of drug inhibition; single lab, single method\",\n      \"pmids\": [\"10600508\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"WDR46 (nucleolar scaffold protein) is required for proper localization of DDX21 to the granular component of the nucleolus. Upon WDR46 knockdown, DDX21 mislocalizes to the edges of nucleoli, and proper DDX21 recruitment after cell division is impaired. WDR46 physically interacts with DDX21 via its intrinsically disordered N- and C-terminal regions.\",\n      \"method\": \"siRNA knockdown, immunofluorescence, co-immunoprecipitation, cell-cycle analysis\",\n      \"journal\": \"Genes to cells\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 / Moderate — direct localization experiment tied to protein interaction; single lab with Co-IP and imaging\",\n      \"pmids\": [\"23848194\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"DDX21 (Gu/Ddx21) is a novel direct interactor of protein phosphatase PP1, identified by mitotic spindle enrichment and mass spectrometry. DDX21 is placed within the toposome (Topoisomerase IIα-containing complex) involved in mitotic chromatin regulation.\",\n      \"method\": \"Mitotic spindle biochemical enrichment, mass spectrometry, co-immunoprecipitation, in vitro binding assay\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — mass spectrometry identification plus Co-IP and direct binding; single lab; no functional mutagenesis\",\n      \"pmids\": [\"22761809\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"At the ENPP2 locus, JMJD3 interacts with DDX21 (identified by mass spectrometry) and recruits DDX21 to the transcription start site and gene body. DDX21 resolves R-loops formed co-transcriptionally at ENPP2, enabling productive transcription. This JMJD3-DDX21 recruitment is controlled by a distant-acting enhancer.\",\n      \"method\": \"Mass spectrometry, co-immunoprecipitation, ChIP-qPCR, DRIP-qPCR (S9.6 antibody), CRISPR-Cas9 enhancer deletion\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal methods (Co-IP, ChIP, DRIP); single lab\",\n      \"pmids\": [\"31251802\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"NAT10 acetyltransferase acetylates DDX21 at K236 and K573, enhancing DDX21 helicase activity to resolve nucleolar R-loops. Acetylation-mimicking DDX21 (2KQ) has increased helicase activity, and acetylation-deficient DDX21 (2KR) has decreased activity in vitro and in cells. NAT10 loss causes nucleolar R-loop accumulation and DNA damage, rescued by co-expression of acetylation-mimicking DDX21.\",\n      \"method\": \"Co-immunoprecipitation, GST pull-down, mass spectrometry for acetylation sites, in vitro helicase assay, immunofluorescence with RNase H control, CRISPR/shRNA knockdown, γH2AX measurement\",\n      \"journal\": \"Cell communication and signaling\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — modification sites identified by MS, mutagenesis (2KQ/2KR) with in vitro helicase assay, genetic rescue in cells; multiple orthogonal methods\",\n      \"pmids\": [\"39394182\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"NAT10 and DDX21 interact with RNase H1 (via BioID proximity labeling confirmed biochemically). Purified NAT10 and DDX21 proteins enhance RNase H1 cleavage rates in vitro. Reduction of either protein decreases PS-ASO activity and increases R-loop levels and impairs pre-rRNA processing.\",\n      \"method\": \"BioID proximity labeling, co-immunoprecipitation, in vitro RNase H1 cleavage assay, DRIP, knockdown, northern blotting\",\n      \"journal\": \"Nucleic acid therapeutics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1–2 / Moderate — in vitro reconstitution of enhanced RNase H1 activity, BioID plus biochemical confirmation; single lab\",\n      \"pmids\": [\"35852833\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"In zebrafish, Ddx21 cell-autonomously regulates lymphatic vessel development by supporting Vegfc-Flt4-driven endothelial cell proliferation. Loss of Ddx21 reduces ribosome biogenesis, upregulates p53 and p21, and causes cell cycle arrest that blocks lymphangiogenesis.\",\n      \"method\": \"Zebrafish genetic screen, morpholino/mutant analysis, cell-autonomous transplantation experiments, immunofluorescence, ribosome biogenesis assays\",\n      \"journal\": \"Nature cell biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic loss-of-function with cell-autonomous transplant, pathway epistasis (p53/p21 upregulation); single study\",\n      \"pmids\": [\"34750583\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"The phosphatase PRL3 binds DDX21 and restricts productive transcription elongation by RNAPII at MITF-regulated endolysosomal vesicle genes, controlling melanocyte stem cell differentiation. PRL3-DDX21 interaction limits transcriptional elongation as a differentiation checkpoint mechanism.\",\n      \"method\": \"Co-immunoprecipitation, ChIP-seq, RNAPII elongation assays, zebrafish genetic analysis, patient melanoma data\",\n      \"journal\": \"Developmental cell\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal Co-IP and ChIP-seq functional readout; single lab with in vivo validation\",\n      \"pmids\": [\"32652076\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"Nucleotide depletion (via DHODH inhibition with leflunomide) reduces DDX21 chromatin occupancy in melanoma cells. Progesterone receptor (Pgr) binds the RNA helicase Ddx21 (proteomics). DDX21 acts as a sensor and mediator of transcription during nucleotide stress, and ddx21-deficient zebrafish show resistance to leflunomide-induced neural crest defects.\",\n      \"method\": \"In vivo chemical suppressor screen (zebrafish), proteomics (Pgr-DDX21 interaction), ChIP-seq, nucleotide supplementation rescue\",\n      \"journal\": \"Nature cell biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vivo genetic evidence plus ChIP-seq; Pgr-DDX21 interaction by proteomics; single lab\",\n      \"pmids\": [\"32231306\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"DDX21 suppresses Snail transcription independently of its helicase activity by recruiting PRC2 subunits SUZ12 and EZH2 to the Snail promoter, establishing a double-negative feedback loop where Snail also represses DDX21 transcription.\",\n      \"method\": \"ChIP assay, co-immunoprecipitation, overexpression/knockdown, luciferase reporter, in vivo metastasis assay\",\n      \"journal\": \"Cancer letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 / Moderate — ChIP showing DDX21 recruits PRC2 to Snail promoter; helicase-dead mutant confirms independence; single lab\",\n      \"pmids\": [\"30165191\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"DDX21 regulates protein expression of MAGED2 through an rG4 structure in the MAGED2 5'-UTR. Cells expressing rG4-binding-deficient DDX21 (M4 mutant) show halved MAGED2 protein (but not mRNA) levels, leading to elevated TRAIL-R2 and TRAIL-mediated apoptosis sensitivity.\",\n      \"method\": \"Label-free proteomics, western blotting, qRT-PCR, rG4-binding-deficient DDX21 mutant expression, TRAIL apoptosis assay\",\n      \"journal\": \"RNA\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 / Moderate — rG4-binding-deficient mutant establishes G4-dependent translational regulation; single lab, proteomic discovery plus follow-up\",\n      \"pmids\": [\"31653714\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"DDX21 interacts with WDR5 and recruits it to the CDK1 gene promoter, enhancing H3K4me3 trimethylation to activate CDK1 transcription in colorectal cancer cells. DDX21 knockdown reduces CDK1 expression and causes G2/M phase arrest.\",\n      \"method\": \"Co-immunoprecipitation, ChIP assay, gene expression profiling, knockdown experiments, cell cycle analysis\",\n      \"journal\": \"Journal of Cancer\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 / Moderate — Co-IP plus ChIP demonstrating recruitment and histone modification; single lab\",\n      \"pmids\": [\"35371306\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"In the context of nuclear RNA activation (RNAa), CDK9 and DDX21 form a complex with nuclear AGO and TNRC6A. DDX21 inhibition suppresses RNAa by miR-34a and other miRNAs without inhibiting post-transcriptional regulation, placing DDX21 as necessary for release of paused RNAPII during RNAa.\",\n      \"method\": \"Co-immunoprecipitation, siRNA knockdown, Pol II ChIP, reporter assay distinguishing transcriptional vs. post-transcriptional regulation\",\n      \"journal\": \"Cell reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 / Moderate — complex identified by Co-IP, functional knockdown with mechanistic readout; single lab\",\n      \"pmids\": [\"35417682\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"DDX21 interacts with AGO2 in the nucleus in an RNA-dependent indirect manner. DDX21 upregulates AGO2 protein levels and participates in AGO2-dependent alternative splicing of SMN2.\",\n      \"method\": \"Co-immunoprecipitation, GST pulldown, immunofluorescence, splicing assays\",\n      \"journal\": \"Bioscience, biotechnology, and biochemistry\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, indirect interaction, limited mechanistic follow-up\",\n      \"pmids\": [\"33604619\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"DDX21 interacts with TERT to regulate rRNA transcription by affecting the binding of RNA Pol I to rDNA. BRAF mutation upregulates DDX21 expression through the MEK/ERK/GABP transcription factor axis (GABPA binds the DDX21 promoter). DDX21 knockdown suppresses multiple cancer hallmark gene expressions.\",\n      \"method\": \"Co-immunoprecipitation, mass spectrometry, ChIP-seq, Ribo-seq, RNA-seq, luciferase reporter assay, MAPK inhibitor treatment\",\n      \"journal\": \"Thyroid\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP identifies DDX21-TERT interaction, ChIP confirms GABPA binding to DDX21 promoter, multiple genomic approaches; single lab\",\n      \"pmids\": [\"41817108\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Calmodulin (CaM) interacts with nucleolar DDX21 in a Ca2+-dependent manner. CaM alters DDX21 conformation to liberate DDX21-sequestered RPA194 (the catalytic subunit of RNA Pol I), facilitating rDNA transcription. This CaM-DDX21 interaction couples activity-induced Ca2+ influx to nucleolar rRNA biogenesis in hippocampal neurons.\",\n      \"method\": \"Co-immunoprecipitation, fluorescence binding assay, Ca2+ chelation, conformation assay, small molecule screening, axon growth assay\",\n      \"journal\": \"The Journal of neuroscience\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP with Ca2+ dependence, conformational change assay, functional rescue; single lab\",\n      \"pmids\": [\"39060175\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"U3 snoRNA is the predominant DDX21-binding partner during mitosis; DDX21 colocalizes with U3 snoRNA in the perichromosomal region (PR). U3 snoRNA regulates DDX21 PR localization by maintaining its mobility; DDX21 knockdown causes mitotic catastrophe similar to U3 snoRNA depletion. In vitro, Cy5-U3 snoRNA downsizes fibrous DDX21 condensates at proper molecular ratios.\",\n      \"method\": \"RIP, immunofluorescence, FRAP, DDX21 knockdown, U3 snoRNA depletion, in vitro condensate assay\",\n      \"journal\": \"Cell death & disease\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — RNA-protein interaction in mitotic context, localization tied to function, in vitro condensate reconstitution; single lab\",\n      \"pmids\": [\"38760378\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"DDX21 undergoes phase separation in vitro and in CRC cells via its intrinsically disordered region (IDR). Phase-separated DDX21 binds the MCM5 gene locus; IDR mutations disrupting phase separation reduce MCM5 binding. MCM5 overexpression rescues the impaired metastatic ability of DDX21-depleted cells, placing MCM5 as a downstream target.\",\n      \"method\": \"In vitro phase separation assay, IDR mutagenesis, ChIP, knockdown/rescue experiments, in vivo metastasis model\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — phase separation reconstituted in vitro, IDR mutants used, genetic epistasis by rescue; single lab\",\n      \"pmids\": [\"37029300\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"LINC00240 lncRNA stabilizes DDX21 protein by recruiting the deubiquitinase USP10, which removes ubiquitin from DDX21 and prevents its proteasomal degradation.\",\n      \"method\": \"Co-immunoprecipitation, ubiquitination assay, USP10 overexpression/knockdown, western blotting\",\n      \"journal\": \"Journal of experimental & clinical cancer research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 / Moderate — Co-IP identifying lncRNA-DDX21-USP10 ternary stabilization; single lab\",\n      \"pmids\": [\"37072811\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"TRIP13 (AAA+ ATPase) directly interacts with DDX21 and stabilizes it by restraining its ubiquitination degradation, promoting gastric cancer progression.\",\n      \"method\": \"Co-immunoprecipitation, ubiquitination assay, knockdown experiments, in vivo tumor model\",\n      \"journal\": \"Cell death & disease\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — Co-IP and ubiquitination assay; single lab, limited mechanistic depth\",\n      \"pmids\": [\"39187490\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"DDX21 competitively binds SIRT7, relieving SIRT7-mediated inhibition of NAT10, thereby upregulating NAT10 expression and enhancing NAT10-mediated ac4C modification of ATAD2, SOX4, and SNX5 mRNAs in colorectal cancer.\",\n      \"method\": \"Co-immunoprecipitation, western blotting, MeRIP for ac4C, knockdown/overexpression, in vivo metastasis model\",\n      \"journal\": \"Cell death & disease\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — Co-IP showing competitive binding; ac4C modification measured; single lab, limited mechanistic resolution\",\n      \"pmids\": [\"40301349\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"The small molecule KI-DX-014 (identified by small-molecule microarray against DDX21) inhibits DDX21-RNA interactions, reduces ATPase activity, modulates biomolecular condensate formation, and attenuates DDX21-dependent P-TEFb release from 7SK snRNP in vitro, suppressing RNAPII CTD phosphorylation.\",\n      \"method\": \"Small-molecule microarray, ATPase assay, condensate formation assay, in vitro 7SK snRNP P-TEFb release assay, zebrafish developmental assay\",\n      \"journal\": \"ACS chemical biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1–2 / Moderate — in vitro biochemical reconstitution of multiple DDX21 functions inhibited by compound; single lab\",\n      \"pmids\": [\"40637641\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"DDX21 inhibits FMDV IRES-dependent translation by binding FMDV IRES domains 2, 3, and 4. FMDV counteracts this by degrading DDX21 via its non-structural proteins 2B and 2C (through the caspase pathway) and 3Cpro (through the lysosomal pathway).\",\n      \"method\": \"Pulldown assay, dual-luciferase assay (IRES activity), knockdown/overexpression, confocal microscopy, pathway inhibitor experiments\",\n      \"journal\": \"Viruses\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 / Moderate — pulldown identifies IRES binding domains, IRES-luciferase assay is functional, degradation pathways distinguished; single lab\",\n      \"pmids\": [\"34578346\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"HTLV-1 Gag interacts with DDX21 through zinc fingers in the NC domain, independently of RNA. DDX21 is packaged into virions. DDX21 alone enhances tRNAPro primer annealing to the HTLV-1 primer binding site, and DDX21 + RPL7 + Gag combination shows synergistic annealing activity.\",\n      \"method\": \"Affinity purification–mass spectrometry, reciprocal co-immunoprecipitation, domain-mapping, in vitro primer-annealing assays\",\n      \"journal\": \"bioRxiv (preprint)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal Co-IP with domain mapping, in vitro functional annealing assay; preprint, single lab\",\n      \"pmids\": [\"40791341\"],\n      \"is_preprint\": true\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Ddx21 interacts with the histone demethylase Kdm5a and co-occupies H3K4me3-marked active promoters. Loss of Ddx21 reduces H3K4me3 at rDNA and hematopoietic genes (cKit, Gata1). Kdm5a inhibition restores rRNA expression and translation in Ddx21-deficient fetal hematopoietic cells, demonstrating that Ddx21 sequesters Kdm5a to maintain active chromatin for ribosomal transcription.\",\n      \"method\": \"Conditional knockout, multi-omics (ChIP-seq, RNA-seq, ribosome profiling), co-immunoprecipitation, Kdm5a inhibitor rescue\",\n      \"journal\": \"bioRxiv (preprint)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP, ChIP-seq, genetic rescue with Kdm5a inhibitor; preprint, single lab\",\n      \"pmids\": [\"bio_10.1101_2025.09.04.674186\"],\n      \"is_preprint\": true\n    }\n  ],\n  \"current_model\": \"DDX21 is a multifunctional nucleolar DEAD-box RNA helicase that coordinates ribosome biogenesis (promoting rRNA transcription, processing, and modification via direct rRNA/snoRNA contacts and nucleolar localization regulated by PARP1-mediated ADP-ribosylation, c-Jun, WDR46, and NAT10-mediated acetylation), controls RNA polymerase II elongation by releasing P-TEFb from 7SK snRNP in a helicase-dependent manner, resolves co-transcriptional R-loops and recruits the m6A methyltransferase METTL3 to promote transcription termination, unwinds RNA G-quadruplexes via its Arg/Gly-rich C-terminus, acts as a dimeric enzyme whose dimerization state regulates both ATPase-dependent and ATP-independent activities, senses transcriptional status and nucleotide availability through chromatin occupancy changes, functions as a cytosolic dsRNA sensor (within a DDX1-DDX21-DHX36-TRIF complex) to activate type I interferon responses, restricts multiple viruses by binding viral polymerase components or IRES elements while being counter-targeted by viral proteins (influenza NS1, DENV NS2B-NS3, FMDV 3Cpro, caspase-dependent cleavage), and responds to glucose by dissociating into monomers that relocalize to the nucleoplasm to regulate mRNA splicing during differentiation.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"DDX21 is a nucleolar DEAD-box RNA helicase that integrates ribosome biogenesis with RNA polymerase activity by directly contacting rRNA, snoRNAs, and 7SK RNA: in the nucleolus it promotes rRNA transcription, processing, and modification, while in the nucleoplasm it binds 7SK snRNP at Pol II promoters and releases P-TEFb in a helicase-dependent manner to drive transcription elongation [#0]. It enforces the ordered hierarchy of pre-40S maturation by recruiting late-acting snoRNPs to pre-rRNA at sites overlapping its own crosslinking footprint [#12], and its activity over Pol I is gated by allosteric inputs—the lncRNA SLERT loosens ring-shaped DDX21 assemblies that otherwise suppress Pol I transcription [#1], and U3 snoRNA tunes its mitotic perichromosomal localization and condensate size [#35]. Crystal structures in apo, pre-hydrolysis, and post-hydrolysis states define an open-to-closed conformational cycle, and DDX21 unwinds dsRNA cooperatively as a dimer whose central dimerization domain is required for both ATP-dependent unwinding and ATP-independent G-quadruplex remodeling, the latter mediated by its Arg/Gly-rich C-terminus [#6, #11, #9]. As a genome-stability factor, DDX21 unwinds R-loops to prevent double-strand breaks, and its helicase activity is set by reversible acetylation (CBP/SIRT7 and NAT10) [#3, #23]; at transcription termination regions it recruits METTL3 to deposit m6A on nascent RNA and promote XRN2-mediated RNAPII termination [#8]. DDX21 localization and abundance are heavily regulated—by c-Jun, WDR46, PARP1-mediated ADP-ribosylation, glucose binding to its ATP pocket, and Ca2+/calmodulin—coupling rRNA biogenesis to cellular state and, upon glucose-driven dimer dissociation and nucleoplasmic relocalization, to mRNA splicing of pro-differentiation genes [#13, #20, #2, #7, #34]. Beyond these nuclear roles, DDX21 acts in cytosolic innate immunity as part of a DDX1-DDX21-DHX36-TRIF dsRNA-sensing complex that activates type I interferon, and it restricts multiple viruses by engaging viral polymerase or IRES components, functions that diverse viral proteins counteract [#4, #5, #41].\",\n  \"teleology\": [\n    {\n      \"year\": 1997,\n      \"claim\": \"Established that DDX21 is a nucleolar protein whose localization is dynamic, revealing that its nucleolar residence reports on transcriptional/metabolic state.\",\n      \"evidence\": \"Immunofluorescence with cytotoxic drug treatment and washout in MCF-7 cells\",\n      \"pmids\": [\"9299166\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No molecular function assigned\", \"Mechanism of translocation unknown\"]\n    },\n    {\n      \"year\": 1999,\n      \"claim\": \"First demonstrated DDX21 is a bona fide RNA helicase, defining its core enzymatic activity on tailed dsRNA substrates.\",\n      \"evidence\": \"Recombinant baculovirus-expressed protein in an in vitro helicase assay\",\n      \"pmids\": [\"10600508\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single substrate type\", \"No cellular substrate identified\", \"Adriamycin inhibition acts via RNA, not protein\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Identified c-Jun as a regulator of DDX21 nucleolar localization, linking an AP-1 transcription factor to rRNA accumulation.\",\n      \"evidence\": \"siRNA knockdown, reciprocal Co-IP, RIP, and rescue with immunofluorescence\",\n      \"pmids\": [\"18180292\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single lab\", \"Mechanism of c-Jun-directed retention unclear\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Placed DDX21 in cytosolic innate immunity as part of a DDX1-DDX21-DHX36-TRIF complex sensing dsRNA, expanding its role beyond the nucleolus.\",\n      \"evidence\": \"Poly I:C affinity purification, mass spectrometry, domain mapping, shRNA knockdown across virus types in dendritic cells\",\n      \"pmids\": [\"21703541\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Stoichiometry of the sensing complex not resolved\", \"How nucleolar DDX21 partitions to cytosol unclear\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Defined DDX21's dual-compartment role in gene expression—nucleolar rRNA control and nucleoplasmic P-TEFb release from 7SK snRNP—and its ordered control of snoRNP-driven pre-40S maturation, establishing it as a master coordinator of ribosome biogenesis and Pol II elongation.\",\n      \"evidence\": \"ChIP-seq, CLIP-seq, RIP, helicase-dead mutants, reporters (Nature); CRAC crosslinking and gradient sedimentation (NAR)\",\n      \"pmids\": [\"25470060\", \"25477391\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How DDX21 selects late vs early snoRNPs unknown\", \"Helicase substrate specificity in vivo not fully mapped\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Showed DDX21 restricts influenza A by binding polymerase subunit PB1, and that viral NS1 displaces PB1, defining a host-virus competition for DDX21.\",\n      \"evidence\": \"Reciprocal Co-IP, domain mapping, NS1 mutant virus with DDX21 knockdown rescue\",\n      \"pmids\": [\"24721576\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether helicase activity is needed for restriction not resolved\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Identified DDX21 as an R-loop resolvase whose activity is set by acetylation (CBP/SIRT7), tying the helicase to genome stability and transcriptional throughput.\",\n      \"evidence\": \"In vitro R-loop unwinding, DRIP-seq, SIRT7/DDX21 double knockdown, acetylation assays, γH2AX\",\n      \"pmids\": [\"28790157\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Genome-wide R-loop targeting determinants incomplete\", \"Acetylation site identity not yet mapped here\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Revealed allosteric regulation of DDX21 by the lncRNA SLERT and visualized ring-shaped DDX21 assemblies suppressing Pol I, showing RNA partners gate its enzymatic state.\",\n      \"evidence\": \"STORM super-resolution imaging, RIP, CRISPR deletion, in vitro binding\",\n      \"pmids\": [\"28475895\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular basis of ring formation unresolved\", \"How SLERT binding propagates to ATPase cycle unclear\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Established the Arg/Gly-rich C-terminus as a direct RNA G-quadruplex binder/unwinder, defining a structure-specific RNA recognition activity distinct from canonical duplex unwinding.\",\n      \"evidence\": \"MS pull-down, fluorescence binding, nuclease sensitivity, domain truncation, mRNA reporter\",\n      \"pmids\": [\"28472472\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single lab\", \"Cellular scope of rG4 targets limited\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Mapped the C-terminal G-quadruplex epitope at residue resolution on TERRA, refining the structural basis of quadruplex specificity.\",\n      \"evidence\": \"In vitro binding and 2D STD NMR with 2'OH mutagenesis\",\n      \"pmids\": [\"29906500\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No in-cell functional consequence measured\", \"Single lab\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Connected nucleolar PARP1/snoRNA signaling to DDX21 via ADP-ribosylation, providing a post-translational switch for its nucleolar retention and rDNA transcription.\",\n      \"evidence\": \"Co-IP, PARP inhibitors, ADP-ribosylation site mutagenesis, Pol I assays, xenografts\",\n      \"pmids\": [\"31351877\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"ADP-ribosylation site residues' structural effect unclear\", \"Crosstalk with acetylation not addressed\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Provided three-state crystal structures and dimerization analysis, defining the conformational cycle and showing dimerization is required for both ATP-dependent and ATP-independent activities.\",\n      \"evidence\": \"X-ray crystallography (apo/AMPPNP-ssRNA/ADP), ATPase and unwinding assays, mutagenesis (Advanced Science); SAXS with dimerization mutants (iScience)\",\n      \"pmids\": [\"32714761\", \"33313488\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Full-length structure including IDR/C-terminus not resolved\", \"Dimer architecture from SAXS only\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Showed glucose directly binds the ATP-binding domain to dissociate DDX21 dimers and trigger nucleoplasmic relocalization toward mRNA splicing, linking metabolic state to a function switch during differentiation.\",\n      \"evidence\": \"Azido-glucose click chemistry, in vitro helicase, SAXS, eCLIP, splicing assays, knockdown/rescue\",\n      \"pmids\": [\"36608661\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Generality of the SCUGSDGC splicing motif across cell types unknown\", \"How monomers recruit splicing factors mechanistically unclear\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Defined a DDX21-METTL3 nexus that couples R-loop recognition and m6A deposition to XRN2-mediated RNAPII termination, integrating DDX21 helicase activity with transcription termination and genome integrity.\",\n      \"evidence\": \"Co-IP, ChIP-seq, MeRIP, DRIP-seq, helicase-dead mutant, XRN2 cleavage assays, γH2AX\",\n      \"pmids\": [\"38569554\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Order of R-loop resolution vs m6A deposition not fully resolved\", \"Direct DDX21-METTL3 interface unmapped\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Identified NAT10 acetylation of DDX21 at K236/K573 as an activating modification for R-loop resolution, and showed DDX21/NAT10 enhance RNase H1 activity, embedding DDX21 in a modification-controlled R-loop clearance network.\",\n      \"evidence\": \"MS acetylation mapping, 2KQ/2KR mutants, in vitro helicase, genetic rescue, γH2AX; BioID and in vitro RNase H1 cleavage assays\",\n      \"pmids\": [\"39394182\", \"35852833\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Interplay of NAT10 acetylation with SIRT7/CBP acetylation not integrated\", \"RNase H1 enhancement mechanism structurally undefined\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Showed Ca2+/calmodulin alters DDX21 conformation to liberate sequestered RPA194 and drive rDNA transcription, coupling neuronal activity-induced calcium signaling to nucleolar biogenesis.\",\n      \"evidence\": \"Co-IP with Ca2+ dependence, conformation assays, small-molecule screen, axon growth assay in hippocampal neurons\",\n      \"pmids\": [\"39060175\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single lab\", \"Generalizability beyond neurons untested\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Demonstrated U3 snoRNA controls mitotic DDX21 perichromosomal localization and condensate behavior, extending DDX21 RNA-dependent regulation into cell division.\",\n      \"evidence\": \"RIP, immunofluorescence, FRAP, knockdown/depletion, in vitro condensate assay\",\n      \"pmids\": [\"38760378\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Functional consequence of perichromosomal DDX21 not fully defined\", \"Single lab\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Identified a selective small-molecule inhibitor (KI-DX-014) that blocks DDX21-RNA binding, ATPase, condensate formation, and 7SK-P-TEFb release, providing a chemical tool validating multiple DDX21 functions.\",\n      \"evidence\": \"Small-molecule microarray, ATPase and condensate assays, in vitro 7SK P-TEFb release, zebrafish developmental assay\",\n      \"pmids\": [\"40637641\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Selectivity over other helicases not exhaustively profiled\", \"In vivo efficacy limited to zebrafish readout\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How the many regulatory inputs (ADP-ribosylation, acetylation, glucose, Ca2+/CaM, dimerization, phase separation, and partner RNAs) are integrated to dynamically partition DDX21 among ribosome biogenesis, transcription elongation/termination, splicing, and immune sensing remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No unified model of compartment-switching control\", \"Crosstalk between PTMs not co-assayed\", \"Full-length structure with IDR and bound regulators lacking\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140098\", \"supporting_discovery_ids\": [0, 3, 6, 8, 9, 19]},\n      {\"term_id\": \"GO:0003723\", \"supporting_discovery_ids\": [0, 9, 10, 12, 18, 35]},\n      {\"term_id\": \"GO:0140657\", \"supporting_discovery_ids\": [6, 11, 18, 40]},\n      {\"term_id\": \"GO:0140299\", \"supporting_discovery_ids\": [4, 7, 27]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005730\", \"supporting_discovery_ids\": [0, 1, 2, 13, 14, 20, 34]},\n      {\"term_id\": \"GO:0005654\", \"supporting_discovery_ids\": [0, 7, 13, 14, 17]},\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [4, 15, 16]},\n      {\"term_id\": \"GO:0000228\", \"supporting_discovery_ids\": [35]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-74160\", \"supporting_discovery_ids\": [0, 8, 22, 26, 31]},\n      {\"term_id\": \"R-HSA-8953854\", \"supporting_discovery_ids\": [0, 7, 12]},\n      {\"term_id\": \"R-HSA-1852241\", \"supporting_discovery_ids\": [1, 2, 12, 25]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [4, 5, 16]},\n      {\"term_id\": \"R-HSA-73894\", \"supporting_discovery_ids\": [3, 8, 23]}\n    ],\n    \"complexes\": [\n      \"7SK snRNP\",\n      \"DDX1-DDX21-DHX36-TRIF dsRNA-sensing complex\"\n    ],\n    \"partners\": [\n      \"METTL3\",\n      \"TRIF\",\n      \"WDR46\",\n      \"SIRT7\",\n      \"NAT10\",\n      \"PARP1\",\n      \"DDX1\",\n      \"DHX36\"\n    ],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":6,"faith_total":6,"faith_pct":100.0}}