{"gene":"SNRNP200","run_date":"2026-04-28T20:42:08","timeline":{"discoveries":[{"year":1998,"finding":"Brr2 (yeast ortholog of SNRNP200) unwinds the U4/U6 RNA duplex in an ATP hydrolysis-dependent manner; immunopurified Brr2 in a native U1/U2/U5/U4/U6 snRNP complex catalyzes U4/U6 base-pair disruption and release of free U4 and U6 snRNPs, and a helicase-domain mutation (brr2-1) abolishes this activity.","method":"Immunopurification of native snRNP complex, ATP hydrolysis assay, helicase-domain point mutant","journal":"Current biology : CB","confidence":"High","confidence_rationale":"Tier 1 — in vitro reconstitution with native complex and active-site mutagenesis, foundational study","pmids":["9705931"],"is_preprint":false},{"year":1998,"finding":"The human U5-200kD protein (SNRNP200/hBrr2) is the subunit of U5 snRNP responsible for ATP-dependent unwinding of U4/U6 RNA duplexes in vitro; activity was traced to the purified 200kD DEXH-box protein after high-salt depletion of U5-100kD from U5 snRNPs.","method":"In vitro U4/U6 RNA unwinding assay with purified HeLa U5 snRNPs; high-salt protein depletion; ion-exchange purification of U5-200kD to homogeneity","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 — in vitro biochemical reconstitution with purified protein, replicated the yeast finding in human system","pmids":["9539711"],"is_preprint":false},{"year":2008,"finding":"ATP-dependent Brr2-mediated dissociation of U4/U6 snRNAs in vitro is stimulated by the C-terminal region of the U5 snRNP protein Prp8 (Prp8-CTR); in contrast, Prp8-CTR simultaneously inhibits U4/U6-dependent ATPase activity; retinitis pigmentosa-linked prp8 alleles fail to stimulate Brr2 unwinding activity.","method":"In vitro U4/U6 unwinding and ATPase assays with purified Prp8 fragments; yeast genetics with RP alleles","journal":"Nature structural & molecular biology","confidence":"High","confidence_rationale":"Tier 1 — reconstituted in vitro with defined components, multiple orthogonal assays","pmids":["19098916"],"is_preprint":false},{"year":2008,"finding":"Brr2, Prp8, and the GTPase Snu114 are localized within distinct domains of the yeast tri-snRNP by electron microscopy: Brr2 occupies a 'head' domain, U4/U6 snRNP forms an 'arm' domain, and Prp8/Snu114 are central; the head and arm adopt variable relative positions suggesting dynamics during activation.","method":"Electron microscopy of genetically tagged tri-snRNP complexes; EM projection structure","journal":"Nature structural & molecular biology","confidence":"Medium","confidence_rationale":"Tier 2 — direct EM localization of tagged proteins within native complex","pmids":["18953335"],"is_preprint":false},{"year":2009,"finding":"Crystal structure of the second Sec63 domain of Brr2 reveals structural similarity to domains 4-5 of DNA helicase Hel308; together with sequence conservation in RecA-like domains, this defines two consecutive Hel308-like modules (Hel308-I and -II) in Brr2; the C-terminal Hel308-II module (Hel308-II) interacts with Prp8 and Snu114 in vitro and in vivo, and Prp8-CTR facilitates binding of the Brr2-Prp8 complex to U4/U6.","method":"Crystal structure determination; in vitro and in vivo interaction assays; mutagenesis coupled with U4/U6 unwinding assays","journal":"Nature structural & molecular biology","confidence":"High","confidence_rationale":"Tier 1 — crystal structure plus mutagenesis plus functional interaction assays","pmids":["19525970"],"is_preprint":false},{"year":2009,"finding":"Crystal structures of the C-terminal Sec63 unit of yeast Brr2 reveal three domains, two of which resemble functional modules of the DNA helicase Hel308; rational mutagenesis and structural modeling show how RecA-like domains and the Sec63 unit form a functional entity mediating unidirectional and processive RNA duplex unwinding.","method":"Crystal structure determination; rational mutagenesis; splicing and U4/U6 di-snRNA unwinding assays","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 1 — crystal structure with mutagenesis and functional assays","pmids":["19716790"],"is_preprint":false},{"year":2009,"finding":"RP-linked mutations S1087L and R1090L in SNRNP200 reside in the ratchet helix of the first Sec63 domain and cause marked defects in U4/U6 snRNA unwinding without affecting U4/U6-U5 snRNP assembly, establishing that hBrr2's RNA unwinding activity is specifically impaired by these mutations.","method":"Yeast functional assays of analogous mutations (N1104L and R1107L in yeast Brr2p); U4/U6 unwinding assays; U4/U6-U5 tri-snRNP assembly assays","journal":"American journal of human genetics","confidence":"High","confidence_rationale":"Tier 1 — in vitro unwinding assays with defined point mutants, linked to disease mechanism","pmids":["19878916"],"is_preprint":false},{"year":2012,"finding":"Human Brr2 contains two ring-like helicase cassettes that intimately interact; only the N-terminal cassette harbors ATPase and helicase activity in isolation, while the C-terminal cassette binds ATP and strongly stimulates the N-terminal helicase; structural features suggest Brr2 loads onto an internal region of U4/U6 di-snRNA via the N-terminal cassette.","method":"Crystal structures; mutagenesis of intercassette interface and C-terminal ATP pocket; RNA-binding and ATPase assays; functional complementation","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 — crystal structure plus mutagenesis plus multiple functional assays","pmids":["23045696"],"is_preprint":false},{"year":2012,"finding":"The RNase H-like (RH) domain of Prp8 binds U4/U6 snRNA at single-stranded regions of U4 and U6 preceding U4/U6 stem I, and blocks Brr2's interaction with the same U4 single-stranded region, thereby inhibiting U4/U6 unwinding; cross-linking/mass spectrometry identifies the RH domain residues contacting U4/U6 snRNA.","method":"RNA binding assays; cross-linking coupled with mass spectrometry; U4/U6 unwinding assays with Prp8 RH domain","journal":"Genes & development","confidence":"High","confidence_rationale":"Tier 1 — biochemical reconstitution with multiple orthogonal methods (CLIP-MS, RNA binding, unwinding)","pmids":["23124066"],"is_preprint":false},{"year":2013,"finding":"The C-terminal tail of Prp8 (Jab1/MPN domain) inserts into Brr2's RNA-binding tunnel, directly competing with RNA substrate binding and thereby reversibly inhibiting Brr2's RNA-binding, ATPase, and U4/U6 unwinding activities; RP-linked Prp8 mutations in the C-terminal tail result in inefficient Brr2 repression.","method":"Crystal structure of Brr2–Prp8 C-terminal tail complex; ATPase assays; RNA-binding assays; U4/U6 unwinding assays","journal":"Science (New York, N.Y.)","confidence":"High","confidence_rationale":"Tier 1 — crystal structure plus multiple biochemical assays, mechanism directly demonstrated","pmids":["23704370"],"is_preprint":false},{"year":2013,"finding":"The Jab1/MPN domain of Prp8 binds exclusively to the N-terminal helicase cassette of yeast Brr2 and stimulates its activity; RP-causing mutations in the Prp8 Jab1/MPN domain are at or near the Brr2 interface; in U5 snRNP biogenesis, Brr2 replaces the assembly factor Aar2 after nuclear import, explaining their mutual exclusivity.","method":"Crystal structure of yeast Brr2–Prp8 Jab1/MPN complex; mutagenesis; biochemical competition assays","journal":"Structure (London, England : 1993)","confidence":"High","confidence_rationale":"Tier 1 — crystal structure with mutagenesis and functional biochemistry","pmids":["23727230"],"is_preprint":false},{"year":2013,"finding":"RP-linked mutations S1087L and R1090L in human BRR2 (SNRNP200) enhance cryptic splice-site recognition and impair proper 5'-splice-site selection; depletion of endogenous BRR2 enhanced usage of a β-globin cryptic splice site, which was restored by wild-type but not RP mutant BRR2.","method":"Stable expression of BAC-recombineered BRR2 mutants in human cell culture; RT-PCR splice-site usage assays; BRR2 knockdown-rescue experiments","journal":"Human mutation","confidence":"Medium","confidence_rationale":"Tier 2 — clean KD/KO with defined cellular phenotype plus mutant rescue in human cells","pmids":["24302620"],"is_preprint":false},{"year":2013,"finding":"Sad1 counteracts Brr2-mediated ATP-dependent dissociation of the U4/U6•U5 tri-snRNP, maintaining tri-snRNP integrity; in the absence of Sad1, Brr2 drives tri-snRNP dissociation into U5 and U4/U6 snRNPs upon ATP hydrolysis.","method":"In vitro tri-snRNP dissociation assay with ATP; yeast genetics; sedimentation analyses","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 1-2 — in vitro reconstitution with purified components plus genetic validation","pmids":["24190974"],"is_preprint":false},{"year":2013,"finding":"U5 snRNA internal loop 1 (IL1) serves as a binding platform for Prp8, Snu114, and Brr2 during U5 snRNP assembly; mutations in both sides of IL1 reduce association of all three proteins with U5 snRNA, and genetic interactions between brr2 alleles and U5 IL1 mutants reveal synthetic lethality.","method":"Yeast in vivo mutagenesis of U5 snRNA; co-immunoprecipitation; genetic synthetic lethality screening","journal":"Journal of cellular biochemistry","confidence":"Medium","confidence_rationale":"Tier 2 — reciprocal in vivo interaction data plus epistasis","pmids":["23857713"],"is_preprint":false},{"year":2015,"finding":"The N-terminal region (~500 residues) of Brr2 encompasses two folded domains and adjacent linear elements that clamp and interconnect the helicase cassettes; it autoinhibits Brr2 via substrate competition and conformational clamping, and is required for stable Brr2 association with tri-snRNP and retention of U5 and U6 snRNAs during spliceosome activation in vivo.","method":"Crystal structure of full-length Brr2 with Prp8 Jab1/MPN domain; cross-linking/mass spectrometry; yeast growth and splicing assays with N-terminal truncations; RNA-binding, ATPase, and helicase assays","journal":"Genes & development","confidence":"High","confidence_rationale":"Tier 1 — crystal structure plus cross-linking MS plus multiple functional assays in vivo and in vitro","pmids":["26637280"],"is_preprint":false},{"year":2015,"finding":"The N-terminal region of Brr2 contains a noncanonical PWI-like domain that does not bind nucleic acids but instead interacts with other spliceosomal proteins including the Prp19 complex protein SPF27, supporting a role of the N-terminal region as a protein-protein interaction platform.","method":"Crystal structure of C. thermophilum Brr2 PWI-like domain; CD spectroscopy; yeast two-hybrid screen against human spliceosomal proteins; band-shift assays","journal":"Acta crystallographica. Section D, Biological crystallography","confidence":"Medium","confidence_rationale":"Tier 1-2 — crystal structure plus interaction screen, but interaction not yet functionally validated","pmids":["25849387"],"is_preprint":false},{"year":2015,"finding":"The N-terminal domain of Brr2 (first ~120 residues) is required for spliceosomal activation beyond U4/U6 unwinding, specifically for retaining U5 and U6 snRNPs during activation; Brr2-Δ120 integrates into tri-snRNP and B complex but fails to maintain U5/U6 during Bact complex formation.","method":"Yeast genetics; yeast growth and splicing assays with N-terminal deletions; spliceosomal complex purification and snRNA composition analysis","journal":"Nucleic acids research","confidence":"Medium","confidence_rationale":"Tier 2 — loss-of-function with defined in vivo splicing phenotype and complex composition analysis","pmids":["25670679"],"is_preprint":false},{"year":2016,"finding":"During Brr2-mediated U4/U6 di-snRNP disruption, Brr2 translocates only a limited distance on the U4 snRNA strand; completion of unwinding requires U6 snRNA to adopt an alternative conformation, releasing Prp3 from U4/U6 di-snRNA while leaving Prp31 and Snu13 bound to U4 snRNA as an intact particle; Brr2 thus strips U6 of all precatalytic binding partners via a substrate-assisted mechanism.","method":"Recombinant in vitro Brr2-mediated U4/U6 di-snRNP disruption system; sequential protein addition assays; mutational analysis of U4/U6 di-snRNA conformation","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 — reconstituted system with defined recombinant components and mechanistic dissection","pmids":["27354531"],"is_preprint":false},{"year":2016,"finding":"SNRNP200 relocalizes into TBK1-containing cytoplasmic structures upon viral infection; its N-terminal Sec63 domain (Sec63-1) binds viral RNA and interacts with TBK1, promoting IRF3 activation and antiviral IFN-β production; the RP-linked S1087L mutant fails to relocalize and cannot rescue antiviral response in knockdown cells.","method":"Knockdown and rescue assays; co-immunoprecipitation with TBK1; RNA binding assays; live-cell imaging of localization upon infection; IFN-β production assays in patient PBMCs","journal":"PLoS pathogens","confidence":"Medium","confidence_rationale":"Tier 2-3 — multiple orthogonal methods but functional rescue is partial and novel non-splicing role","pmids":["27454487"],"is_preprint":false},{"year":2016,"finding":"RP mutations in the ratchet helix of Brr2 (S1087L, R1090L and analogues) exhibit a gradient of weakened RNA binding, reduced helicase activity, and reduced ATPase activity; the Prp8 Jab1/MPN domain increases wild-type Brr2 RNA binding and ATPase activity but does not differentially rescue RP mutants; RP mutant Brr2 proteins capable of RNA binding cannot fully unwind even short duplexes, suggesting impaired translocation.","method":"In vitro biochemical assays (RNA binding, ATPase, helicase) with purified RP-mutant Brr2 proteins; Prp8 Jab1 domain stimulation assays","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — systematic in vitro characterization with purified mutant proteins and multiple assays","pmids":["27072132"],"is_preprint":false},{"year":2016,"finding":"Brr2 autoinhibition (via N-terminal region) and Jab1-mediated inhibition (via Prp8 C-terminal tail insertion into RNA-binding tunnel) act in concert; the N-terminal region influences how the Jab1 tail interacts at the RNA-binding tunnel; N-terminal region specifically interferes with accommodation of double-stranded RNA, while the Jab1 tail interferes with single-stranded RNA, and regulation from the N-terminal region requires the inactive C-terminal helicase cassette.","method":"Crystal structures of S. cerevisiae and C. thermophilum Brr2-Jab1 complexes; systematic RNA binding and unwinding studies with truncation and mutant variants","journal":"Cell cycle (Georgetown, Tex.)","confidence":"High","confidence_rationale":"Tier 1 — crystal structures from two organisms plus systematic biochemical dissection","pmids":["27880071"],"is_preprint":false},{"year":2017,"finding":"FBP21 uses an intrinsically disordered C-terminal region to bind the C-terminal Sec63 unit of Brr2, allosterically inhibiting Brr2 helicase activity; direct interaction of FBP21 with U4/U6 di-snRNA further reduces the pool of unwound U4/U6 di-snRNA.","method":"Yeast two-hybrid; analytical SEC; surface plasmon resonance; peptide SPOT analysis; RNA binding and unwinding assays","journal":"Nucleic acids research","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal biochemical methods establishing binding site and functional consequence","pmids":["28838205"],"is_preprint":false},{"year":2017,"finding":"Two distinct small-molecule inhibitors of Brr2 were identified: one binds an allosteric site between the C-terminal and N-terminal helicase cassettes and is Brr2-selective, and another binds the RNA-binding site inside the N-terminal cassette; co-crystal structures revealed binding modes.","method":"HTS ATPase assay; co-crystal structures; helicase inhibition assays; selectivity profiling","journal":"Journal of medicinal chemistry","confidence":"High","confidence_rationale":"Tier 1 — co-crystal structures with functional validation","pmids":["28586220"],"is_preprint":false},{"year":2018,"finding":"Ntr2, an intrinsically disordered yeast spliceosomal disassembly factor, binds via its N-terminal region to the C-terminal helicase unit of Brr2 and downregulates Brr2 helicase activity in vitro by modulating the fraction of helicase molecules productively bound to RNA substrate.","method":"CD spectroscopy; DLS; NMR spectroscopy; peptide SPOT analyses; analytical SEC; SPR; RNA binding and unwinding assays","journal":"Biophysical journal","confidence":"High","confidence_rationale":"Tier 1-2 — multiple biophysical methods identifying binding site plus functional consequence in vitro","pmids":["29490241"],"is_preprint":false},{"year":2019,"finding":"The inactive C-terminal cassette of BRR2 can both stimulate and inhibit the RNA-unwinding activity of the N-terminal cassette depending on the relative orientation of the two cassettes; engineered disulfide bridges locking cassettes in two different orientations had opposite effects (one enhancing, one inhibiting) on RNA unwinding and ATP hydrolysis.","method":"Crystal structure of BRR2 with Prp8 activating domain at 2.4 Å; engineered disulfide bridges; RNA unwinding and ATPase assays; comparison with spliceosomal cryo-EM structures","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — crystal structure plus engineered constraints with direct functional readouts","pmids":["31914407"],"is_preprint":false},{"year":2021,"finding":"Both BRR2 cassettes bind adenine nucleotides with high specificity; the inactive C-terminal cassette binds ADP >100-fold more tightly than the active N-terminal cassette; abrogation of nucleotide binding at the C-terminal cassette reduces nucleotide affinity at the N-terminal cassette 70 Å away via long-range allosteric communication mediated primarily across the intercassette interface.","method":"Biophysical nucleotide binding assays; mutations at intercassette surfaces; molecular dynamics simulations","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1-2 — biophysical assays plus computational validation with mutagenesis confirming allosteric pathway","pmids":["34048711"],"is_preprint":false},{"year":2022,"finding":"C9ORF78 tightly interacts with BRR2 at a multi-factor trafficking site on the C-terminal helicase cassette, occupying a binding surface that FBP21 also uses in a mutually exclusive manner; cryo-EM structures reveal how C9ORF78 and FBP21 wrap around the C-terminal helicase cassette; C9ORF78 knockdown leads to alternative NAGNAG 3'-splice site usage and BRR2-dependent exon skipping.","method":"Cryo-EM structures; in vitro binding assays; affinity purification/mass spectrometry; RNA UV-crosslinking; knockdown with alternative splicing analysis","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 1 — cryo-EM structures plus multiple functional assays establishing regulatory role","pmids":["35241646"],"is_preprint":false},{"year":2022,"finding":"A C. elegans forward genetic screen identified a suppressor allele in SNRNP200/BRR2 (N18K at the unstructured N-terminus) that suppresses 5'-splice-site identity defects, revealing a conserved role for SNRNP200 in maintaining 5'-splice-site identity during spliceosome assembly.","method":"Forward genetic screen in C. elegans; mRNA-seq; double-mutant analysis; mapping of suppressor residues on cryo-EM spliceosome structures","journal":"Nucleic acids research","confidence":"Medium","confidence_rationale":"Tier 2 — genetic epistasis screen with functional mRNA-seq validation in a relevant model organism","pmids":["36321655"],"is_preprint":false},{"year":2024,"finding":"Glucose-induced acetylation of SNRNP200 at K1610 prevents its proteasomal degradation; stabilized SNRNP200 then facilitates splicing of metabolic enzyme-encoding pre-mRNAs (GAPDH, ALDOA, GSS), increasing lactic acid and glutathione production in triple-negative breast cancer.","method":"Mass spectrometry identification of acetylation site; proteasome inhibition/ubiquitination assays; splicing assays; metabolic readouts","journal":"Cell discovery","confidence":"Medium","confidence_rationale":"Tier 2 — identification of PTM with defined functional consequence, single lab study","pmids":["39285160"],"is_preprint":false},{"year":2025,"finding":"RP-linked mutations S1087L and R1090L in SNRNP200 broaden its binding profile on U4 snRNA upstream of U4/U6 stem I as measured by iCLIP, indicating impaired snRNA unwinding activity; this was confirmed by FRAP measurements and in vitro helicase activity assays comparing mutant and wild-type protein.","method":"iCLIP in HeLa and RPE cells; FRAP; in vitro helicase activity assays","journal":"Cellular and molecular life sciences : CMLS","confidence":"High","confidence_rationale":"Tier 1-2 — multiple orthogonal methods (iCLIP, FRAP, in vitro helicase) confirming mechanism of RP mutations","pmids":["40045025"],"is_preprint":false},{"year":2025,"finding":"Y4 RNA fragment (YF1) binds to SNRNP200 and reduces its ubiquitination, stabilizing SNRNP200, which in turn enhances IL-10 pre-mRNA splicing in macrophages; this effect is reversed by a specific SNRNP200 inhibitor (Brr2-IN-3).","method":"Co-immunoprecipitation; ubiquitination assays; mRNA splicing ratio assays; pharmacological inhibition with Brr2-IN-3","journal":"Molecular therapy : the journal of the American Society of Gene Therapy","confidence":"Medium","confidence_rationale":"Tier 3 — single lab, Co-IP and functional assay with inhibitor validation","pmids":["39935176"],"is_preprint":false},{"year":2025,"finding":"BRR2/Brr2 functions as an evolutionarily conserved ciR-loop (circRNA-associated R-loop) repressor with dual roles: inhibiting circRNA generation and resolving ciR-loops; loss of Brr2 leads to ciR-loop accumulation, antisense transcription, premature transcription termination, DNA damage, and defects in DNA replication and cell division.","method":"Loss-of-function genetics; R-loop detection assays; RNA-seq; DNA damage assays; cell cycle analysis","journal":"Nature communications","confidence":"Medium","confidence_rationale":"Tier 2 — defined loss-of-function phenotypes with multiple readouts, novel role outside splicing","pmids":["41093835"],"is_preprint":false},{"year":2013,"finding":"Dominant-negative mutation in the helicase domain I of human U5-200kD (SNRNP200) expressed in HEK293 cells causes delayed exit from G2/M phase due to splicing defects; shRNA-mediated knockdown of U5-200kD causes S-phase arrest.","method":"Dominant-negative expression in ecdysone-inducible system; shRNA knockdown; cell cycle analysis; RT-PCR splicing assays","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2 — loss-of-function and dominant-negative with defined cell cycle phenotypes in human cells","pmids":["23637979"],"is_preprint":false}],"current_model":"SNRNP200 (hBrr2) is a Ski2-like DEXH-box RNA helicase and permanent U5 snRNP component that drives spliceosome activation by using ATP-driven translocation along U4 snRNA to unwind the U4/U6 duplex, a process regulated through multiple cis-mechanisms (autoinhibitory N-terminal region, stimulatory but inactive C-terminal helicase cassette, and long-range allosteric communication between cassettes) and trans-mechanisms (inhibition or activation by consecutive RNase H-like and Jab1/MPN-like domains of Prp8 inserting into Brr2's RNA-binding tunnel, inhibition by FBP21, Ntr2, and C9ORF78 at the C-terminal cassette), with retinitis pigmentosa-linked ratchet-helix mutations specifically impairing RNA unwinding and translocation without disrupting snRNP assembly."},"narrative":{"teleology":[{"year":1998,"claim":"Identification of the U4/U6 unwinding activity resolved which snRNP subunit drives spliceosome activation: both yeast Brr2 and human U5-200kD were shown to catalyze ATP-dependent U4/U6 duplex disruption, establishing the core enzymatic function of SNRNP200.","evidence":"Immunopurified native snRNP complex unwinding assays with helicase-dead mutant (yeast); purified U5-200kD from HeLa U5 snRNPs (human)","pmids":["9705931","9539711"],"confidence":"High","gaps":["Substrate specificity and loading mechanism on U4/U6 not yet defined","Role of other U5 snRNP proteins in regulating unwinding unknown"]},{"year":2008,"claim":"Discovery that Prp8's C-terminal region simultaneously stimulates U4/U6 unwinding while inhibiting ATPase activity established that Brr2 is subject to complex trans-regulation by its stable binding partner, and linked retinitis pigmentosa-associated Prp8 mutations to defective Brr2 regulation.","evidence":"In vitro unwinding and ATPase assays with purified Prp8 fragments; RP allele testing in yeast","pmids":["19098916"],"confidence":"High","gaps":["Molecular basis of dual stimulation/inhibition not structurally resolved","How Prp8 regulation is switched on/off during the splicing cycle unknown"]},{"year":2009,"claim":"Crystal structures of Brr2 Sec63 domains revealed a dual Hel308-like module architecture and showed that the C-terminal module mediates Prp8/Snu114 interaction, while RP mutations S1087L and R1090L in the ratchet helix of the first Sec63 domain specifically impair U4/U6 unwinding without disrupting tri-snRNP assembly, pinpointing the disease mechanism.","evidence":"Crystal structures; rational mutagenesis; U4/U6 unwinding and tri-snRNP assembly assays in yeast and human systems","pmids":["19525970","19716790","19878916"],"confidence":"High","gaps":["Full-length Brr2 structure not yet available","Translocation mechanism along U4 snRNA not defined"]},{"year":2012,"claim":"Structural and functional analysis of full dual-cassette Brr2 revealed that only the N-terminal cassette is catalytically active while the C-terminal cassette acts as a regulatory cofactor, and separately showed that Prp8's RNase H domain blocks Brr2 loading onto U4 snRNA, defining two layers of Prp8-mediated inhibition.","evidence":"Crystal structures of dual-cassette Brr2; mutagenesis of intercassette interface and ATP pocket; cross-linking/MS mapping of Prp8 RH–U4/U6 contacts; RNA binding and unwinding assays","pmids":["23045696","23124066"],"confidence":"High","gaps":["How the two Prp8 inhibitory mechanisms (RH domain and Jab1 tail) are coordinated temporally unknown","Nucleotide occupancy states of C-terminal cassette during splicing not determined"]},{"year":2013,"claim":"Crystal structures of the Prp8 Jab1/MPN domain bound to Brr2 revealed a direct inhibitory mechanism—the Jab1 C-terminal tail inserts into Brr2's RNA-binding tunnel, competing with substrate—and showed that RP-linked Prp8 mutations weaken this inhibition; concurrently, Sad1 was shown to counteract premature Brr2-mediated tri-snRNP disruption, and RP Brr2 mutations were found to alter splice-site selection in human cells.","evidence":"Co-crystal structures of Brr2–Jab1 (human and yeast); ATPase/unwinding assays; tri-snRNP dissociation assays; knockdown-rescue with RP mutants in human cells","pmids":["23704370","23727230","24190974","24302620"],"confidence":"High","gaps":["Mechanism by which Jab1 tail is withdrawn to activate Brr2 in the spliceosome unknown","Whether Sad1 directly contacts Brr2 or acts indirectly not resolved"]},{"year":2015,"claim":"The ~500-residue N-terminal region of Brr2 was shown to act as a cis-autoinhibitory element that clamps the two helicase cassettes, competes with dsRNA substrate, and is required beyond U4/U6 unwinding for retaining U5 and U6 snRNAs during spliceosome activation.","evidence":"Crystal structure of full-length Brr2–Jab1 complex; N-terminal truncation mutants assayed for RNA binding, ATPase, helicase activity, and spliceosomal complex composition in vivo","pmids":["26637280","25670679"],"confidence":"High","gaps":["How N-terminal autoinhibition is relieved during the B-to-Bact transition not determined","Identity of signals triggering relief of autoinhibition unknown"]},{"year":2016,"claim":"Mechanistic dissection established that Brr2 translocates only a limited distance on U4 snRNA and relies on U6 snRNA conformational rearrangement (substrate-assisted unwinding) to complete U4/U6 disruption; separately, RP ratchet-helix mutations were shown to impair translocation specifically, and dual autoinhibition by the N-terminal region and Jab1 tail was shown to target dsRNA vs ssRNA accommodation differentially.","evidence":"Reconstituted U4/U6 di-snRNP disruption with recombinant components; systematic biochemical characterization of RP mutants; crystal structures from two organisms with truncation/mutant RNA binding studies","pmids":["27454531","27072132","27880071"],"confidence":"High","gaps":["Step-size and processivity of Brr2 translocation not quantified","Whether substrate-assisted mechanism operates in the context of the full spliceosome not tested"]},{"year":2017,"claim":"Trans-regulators binding the C-terminal cassette were identified: FBP21 uses an intrinsically disordered region to allosterically inhibit Brr2, while small-molecule inhibitors targeting both allosteric and active sites were co-crystallized, validating druggability of the intercassette interface.","evidence":"SPR, analytical SEC, peptide SPOT analysis, unwinding assays (FBP21); HTS and co-crystal structures (inhibitors)","pmids":["28838205","28586220"],"confidence":"High","gaps":["In vivo functional consequence of FBP21-mediated inhibition not demonstrated","Selectivity and efficacy of inhibitors in splicing-dependent cellular assays not shown"]},{"year":2019,"claim":"Engineered disulfide bridges locking the two cassettes in distinct relative orientations demonstrated that intercassette rotation can either stimulate or inhibit unwinding, establishing that the C-terminal cassette acts as a conformational switch rather than a simple stimulator.","evidence":"Crystal structure of BRR2–Prp8 activating domain; disulfide-locked variants; ATPase and helicase assays","pmids":["31914407"],"confidence":"High","gaps":["Which cassette orientation is adopted at each spliceosomal stage not mapped","Whether intercassette rotation is actively driven or passive unknown"]},{"year":2021,"claim":"Nucleotide-binding measurements revealed that the C-terminal cassette binds ADP >100-fold more tightly than the N-terminal cassette, and long-range allosteric communication across the intercassette interface was demonstrated: disrupting nucleotide binding at the C-terminal cassette reduced affinity at the N-terminal cassette 70 Å away.","evidence":"Biophysical nucleotide binding assays; intercassette interface mutations; molecular dynamics simulations","pmids":["34048711"],"confidence":"High","gaps":["Identity of the allosteric pathway residues at atomic resolution incomplete","Whether ADP/ATP exchange at the C-terminal cassette occurs during the splicing cycle unknown"]},{"year":2022,"claim":"Cryo-EM structures of C9ORF78 and FBP21 bound to Brr2's C-terminal cassette identified a shared, mutually exclusive regulatory site ('multi-factor trafficking site'), and C9ORF78 knockdown produced BRR2-dependent splicing changes including alternative 3'-splice-site usage, establishing the C-terminal cassette as a regulatory hub for sequential trans-factor engagement.","evidence":"Cryo-EM structures; affinity purification/MS; RNA UV-crosslinking; knockdown with splicing analysis","pmids":["35241646"],"confidence":"High","gaps":["Order of factor exchange at the C-terminal cassette during splicing cycle not resolved","Whether additional factors share this binding surface unknown"]},{"year":2025,"claim":"iCLIP mapping of RP mutant Brr2 in living cells showed broadened binding on U4 snRNA upstream of stem I, directly demonstrating impaired translocation in vivo; separately, Brr2 was identified as a repressor of circRNA-associated R-loops (ciR-loops), with loss of function causing R-loop accumulation, DNA damage, and replication defects.","evidence":"iCLIP in HeLa/RPE cells plus FRAP and in vitro helicase assays (RP mutations); loss-of-function genetics with R-loop detection and DNA damage assays (ciR-loop role)","pmids":["40045025","41093835"],"confidence":"High","gaps":["Whether the ciR-loop repression function requires Brr2's helicase activity or is independent unknown","Cell-type specificity of RP mutant translocation defects not fully explored"]},{"year":null,"claim":"How the multiple inhibitory and stimulatory inputs on Brr2 (N-terminal autoinhibition, Prp8 RH domain, Prp8 Jab1 tail, C-terminal cassette orientation, and trans-factors at the C-terminal cassette) are temporally coordinated across spliceosomal stages to achieve precisely timed activation and subsequent disassembly remains unresolved.","evidence":"","pmids":[],"confidence":"Low","gaps":["Time-resolved single-molecule studies of Brr2 regulation during a complete splicing cycle are lacking","Whether Brr2's non-splicing roles (innate immunity, ciR-loop resolution) share the same regulatory architecture is unknown","Structural basis for how the N-terminal PWI-like domain engages downstream spliceosomal factors during activation not determined"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140657","term_label":"ATP-dependent activity","supporting_discovery_ids":[0,1,7,19,25]},{"term_id":"GO:0003723","term_label":"RNA binding","supporting_discovery_ids":[0,1,8,17,29]},{"term_id":"GO:0140098","term_label":"catalytic activity, acting on RNA","supporting_discovery_ids":[0,1,7,17,19]}],"localization":[{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[3,13,16]},{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[18]}],"pathway":[{"term_id":"R-HSA-8953854","term_label":"Metabolism of RNA","supporting_discovery_ids":[0,1,6,7,11,17,27,28,29]},{"term_id":"R-HSA-1643685","term_label":"Disease","supporting_discovery_ids":[6,11,19,29]}],"complexes":["U5 snRNP","U4/U6.U5 tri-snRNP"],"partners":["PRPF8","SNU114","FBP21","C9ORF78","NTR2","SAD1","SPF27"],"other_free_text":[]},"mechanistic_narrative":"SNRNP200 (hBrr2) is a Ski2-like DEXH-box RNA helicase and permanent U5 snRNP component that drives spliceosome activation by ATP-dependent unwinding of the U4/U6 snRNA duplex, a prerequisite for catalytic core formation [PMID:9705931, PMID:9539711]. The enzyme contains two tandem Hel308-like helicase cassettes: only the N-terminal cassette is catalytically active, while the C-terminal cassette binds nucleotides and allosterically modulates unwinding through long-range intercassette communication and orientation-dependent stimulation or inhibition [PMID:23045696, PMID:34048711, PMID:31914407]. Multiple regulatory mechanisms converge on Brr2, including autoinhibition by its N-terminal region, inhibition by insertion of the Prp8 Jab1/MPN C-terminal tail into the RNA-binding tunnel, competition by the Prp8 RNase H domain for the U4 snRNA loading site, and modulation by trans-acting factors (FBP21, Ntr2, C9ORF78) that bind the C-terminal cassette [PMID:26637280, PMID:23704370, PMID:23124066, PMID:28838205, PMID:35241646]. Retinitis pigmentosa-causing missense mutations in the ratchet helix (S1087L, R1090L) specifically impair RNA translocation and unwinding without disrupting tri-snRNP assembly, leading to aberrant splice-site selection [PMID:19878916, PMID:27072132, PMID:24302620]."},"prefetch_data":{"uniprot":{"accession":"O75643","full_name":"U5 small nuclear ribonucleoprotein 200 kDa helicase","aliases":["Activating signal cointegrator 1 complex subunit 3-like 1","BRR2 homolog","U5 snRNP-specific 200 kDa protein","U5-200KD"],"length_aa":2136,"mass_kda":244.5,"function":"Catalyzes the ATP-dependent unwinding of U4/U6 RNA duplices, an essential step in the assembly of a catalytically active spliceosome (PubMed:35241646). Plays a role in pre-mRNA splicing as a core component of precatalytic, catalytic and postcatalytic spliceosomal complexes (PubMed:28502770, PubMed:28781166, PubMed:29301961, PubMed:29360106, PubMed:29361316, PubMed:30315277, PubMed:30705154, PubMed:30728453). As a component of the minor spliceosome, involved in the splicing of U12-type introns in pre-mRNAs (Probable). Involved in spliceosome assembly, activation and disassembly. Mediates changes in the dynamic network of RNA-RNA interactions in the spliceosome","subcellular_location":"Nucleus","url":"https://www.uniprot.org/uniprotkb/O75643/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":true,"resolved_as":"","url":"https://depmap.org/portal/gene/SNRNP200","classification":"Common 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CONDCAC","url":"https://www.omim.org/entry/620636"},{"mim_id":"619569","title":"CHROMOSOME 9 OPEN READING FRAME 78; C9ORF78","url":"https://www.omim.org/entry/619569"},{"mim_id":"617365","title":"AAR2 SPLICING FACTOR; AAR2","url":"https://www.omim.org/entry/617365"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Nucleoplasm","reliability":"Supported"},{"location":"Primary cilium","reliability":"Additional"},{"location":"Cytosol","reliability":"Additional"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/SNRNP200"},"hgnc":{"alias_symbol":["U5-200KD","HELIC2","KIAA0788","Brr2"],"prev_symbol":["ASCC3L1","RP33"]},"alphafold":{"accession":"O75643","domains":[{"cath_id":"-","chopping":"99-179","consensus_level":"high","plddt":77.8672,"start":99,"end":179},{"cath_id":"-","chopping":"267-375","consensus_level":"high","plddt":76.9809,"start":267,"end":375},{"cath_id":"3.40.50.300","chopping":"432-452_684-885","consensus_level":"medium","plddt":87.0706,"start":432,"end":885},{"cath_id":"3.40.50.300","chopping":"458-681","consensus_level":"medium","plddt":87.9574,"start":458,"end":681},{"cath_id":"1.10.10.10","chopping":"903-992","consensus_level":"medium","plddt":90.4129,"start":903,"end":992},{"cath_id":"1.10.3380.10","chopping":"994-1126","consensus_level":"medium","plddt":90.9702,"start":994,"end":1126},{"cath_id":"1.10.150.20","chopping":"1127-1182","consensus_level":"medium","plddt":90.8384,"start":1127,"end":1182},{"cath_id":"3.40.50.300","chopping":"1524-1719","consensus_level":"medium","plddt":89.8447,"start":1524,"end":1719},{"cath_id":"1.10.150.20","chopping":"1959-2013","consensus_level":"medium","plddt":87.6184,"start":1959,"end":2013},{"cath_id":"2.60.40.150","chopping":"2016-2136","consensus_level":"medium","plddt":85.0404,"start":2016,"end":2136}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/O75643","model_url":"https://alphafold.ebi.ac.uk/files/AF-O75643-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-O75643-F1-predicted_aligned_error_v6.png","plddt_mean":82.75},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=SNRNP200","jax_strain_url":"https://www.jax.org/strain/search?query=SNRNP200"},"sequence":{"accession":"O75643","fasta_url":"https://rest.uniprot.org/uniprotkb/O75643.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/O75643/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/O75643"}},"corpus_meta":[{"pmid":"9705931","id":"PMC_9705931","title":"RNA 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Genes PRPF31, PRPF8, and SNRNP200 in Chinese Families with Autosomal Dominant Retinitis Pigmentosa.","date":"2018","source":"Current molecular medicine","url":"https://pubmed.ncbi.nlm.nih.gov/30360737","citation_count":10,"is_preprint":false},{"pmid":"35241646","id":"PMC_35241646","title":"A multi-factor trafficking site on the spliceosome remodeling enzyme BRR2 recruits C9ORF78 to regulate alternative splicing.","date":"2022","source":"Nature communications","url":"https://pubmed.ncbi.nlm.nih.gov/35241646","citation_count":10,"is_preprint":false},{"pmid":"31260034","id":"PMC_31260034","title":"Genotype-Phenotype Analysis of a Novel Recessive and a Recurrent Dominant SNRNP200 Variant Causing Retinitis Pigmentosa.","date":"2019","source":"Investigative ophthalmology & visual science","url":"https://pubmed.ncbi.nlm.nih.gov/31260034","citation_count":10,"is_preprint":false},{"pmid":"26137319","id":"PMC_26137319","title":"Knocking Down Snrnp200 Initiates Demorphogenesis of Rod Photoreceptors in Zebrafish.","date":"2015","source":"Journal of ophthalmology","url":"https://pubmed.ncbi.nlm.nih.gov/26137319","citation_count":9,"is_preprint":false},{"pmid":"33553197","id":"PMC_33553197","title":"SNRNP200 Mutations Cause Autosomal Dominant Retinitis Pigmentosa.","date":"2021","source":"Frontiers in medicine","url":"https://pubmed.ncbi.nlm.nih.gov/33553197","citation_count":9,"is_preprint":false},{"pmid":"23154979","id":"PMC_23154979","title":"Spliceosome activation: U4 is the path, stem I is the goal, and Prp8 is the keeper. Let's cheer for the ATPase Brr2!","date":"2012","source":"Genes & development","url":"https://pubmed.ncbi.nlm.nih.gov/23154979","citation_count":9,"is_preprint":false},{"pmid":"38517341","id":"PMC_38517341","title":"Tracing Allostery in the Spliceosome Ski2-like RNA Helicase Brr2.","date":"2024","source":"The journal of physical chemistry letters","url":"https://pubmed.ncbi.nlm.nih.gov/38517341","citation_count":8,"is_preprint":false},{"pmid":"39285160","id":"PMC_39285160","title":"Targeting SNRNP200-induced splicing dysregulation offers an immunotherapy opportunity for glycolytic triple-negative breast cancer.","date":"2024","source":"Cell discovery","url":"https://pubmed.ncbi.nlm.nih.gov/39285160","citation_count":8,"is_preprint":false},{"pmid":"33203369","id":"PMC_33203369","title":"Depletion of SNRNP200 inhibits the osteo-/dentinogenic differentiation and cell proliferation potential of stem cells from the apical papilla.","date":"2020","source":"BMC developmental biology","url":"https://pubmed.ncbi.nlm.nih.gov/33203369","citation_count":7,"is_preprint":false},{"pmid":"36321655","id":"PMC_36321655","title":"A forward genetic screen in C. elegans identifies conserved residues of spliceosomal proteins PRP8 and SNRNP200/BRR2 with a role in maintaining 5' splice site identity.","date":"2022","source":"Nucleic acids research","url":"https://pubmed.ncbi.nlm.nih.gov/36321655","citation_count":5,"is_preprint":false},{"pmid":"30133436","id":"PMC_30133436","title":"Specification of Drosophila neuropeptidergic neurons by the splicing component brr2.","date":"2018","source":"PLoS genetics","url":"https://pubmed.ncbi.nlm.nih.gov/30133436","citation_count":5,"is_preprint":false},{"pmid":"40045025","id":"PMC_40045025","title":"Retinitis pigmentosa-linked mutations impair the snRNA unwinding activity of SNRNP200 and reduce pre-mRNA binding of PRPF8.","date":"2025","source":"Cellular and molecular life sciences : CMLS","url":"https://pubmed.ncbi.nlm.nih.gov/40045025","citation_count":4,"is_preprint":false},{"pmid":"33429167","id":"PMC_33429167","title":"Generation of two induced pluripotent stem cell lines from a patient with recessive inherited retinal disease caused by compound heterozygous mutations in SNRNP200.","date":"2021","source":"Stem cell research","url":"https://pubmed.ncbi.nlm.nih.gov/33429167","citation_count":4,"is_preprint":false},{"pmid":"41093835","id":"PMC_41093835","title":"Dual roles of DEAD-box RNA helicase Brr2 in genome stability regulation.","date":"2025","source":"Nature communications","url":"https://pubmed.ncbi.nlm.nih.gov/41093835","citation_count":3,"is_preprint":false},{"pmid":"34048711","id":"PMC_34048711","title":"Long-range allostery mediates cooperative adenine nucleotide binding by the Ski2-like RNA helicase Brr2.","date":"2021","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/34048711","citation_count":3,"is_preprint":false},{"pmid":"39935176","id":"PMC_39935176","title":"Y4 RNA fragment alleviates myocardial injury in heart transplantation via SNRNP200 to enhance IL-10 mRNA splicing.","date":"2025","source":"Molecular therapy : the journal of the American Society of Gene Therapy","url":"https://pubmed.ncbi.nlm.nih.gov/39935176","citation_count":2,"is_preprint":false},{"pmid":"28118396","id":"PMC_28118396","title":"Correction: Spliceosome SNRNP200 Promotes Viral RNA Sensing and IRF3 Activation of Antiviral Response.","date":"2017","source":"PLoS pathogens","url":"https://pubmed.ncbi.nlm.nih.gov/28118396","citation_count":2,"is_preprint":false},{"pmid":"30558886","id":"PMC_30558886","title":"FBP21's C-Terminal Domain Remains Dynamic When Wrapped around the c-Sec63 Unit of Brr2 Helicase.","date":"2018","source":"Biophysical journal","url":"https://pubmed.ncbi.nlm.nih.gov/30558886","citation_count":2,"is_preprint":false},{"pmid":"24499697","id":"PMC_24499697","title":"[Targeted sequencing identifies a hotspot mutation SNRNP200 p.S1087L correlates with novel phenotypes in retinitis pigmentosa].","date":"2013","source":"[Zhonghua yan ke za zhi] Chinese journal of ophthalmology","url":"https://pubmed.ncbi.nlm.nih.gov/24499697","citation_count":1,"is_preprint":false},{"pmid":"36974964","id":"PMC_36974964","title":"Conformation-dependent ligand hot spots in the spliceosomal RNA helicase BRR2.","date":"2023","source":"Acta crystallographica. Section D, Structural biology","url":"https://pubmed.ncbi.nlm.nih.gov/36974964","citation_count":0,"is_preprint":false},{"pmid":"41427026","id":"PMC_41427026","title":"Likely Pathogenic/Pathogenic Variants in the Spliceosome Complex Genes SNRNP200, SF3B1, SF3B2, and SF3B4 Implicated in Nonsyndromic Orofacial Cleft.","date":"2025","source":"Human mutation","url":"https://pubmed.ncbi.nlm.nih.gov/41427026","citation_count":0,"is_preprint":false},{"pmid":"33201471","id":"PMC_33201471","title":"Characterization of the Brr2 RNA Helicase and Its Regulation by Other Spliceosomal Proteins Using Gel-Based U4/U6 Di-snRNA Binding and Unwinding Assays.","date":"2021","source":"Methods in molecular biology (Clifton, N.J.)","url":"https://pubmed.ncbi.nlm.nih.gov/33201471","citation_count":0,"is_preprint":false},{"pmid":null,"id":"bio_10.1101_2025.03.03.25321546","title":"Genomic Modifiers of Neurological Resilience in a Niemann-Pick C family","date":"2025-03-06","source":"bioRxiv","url":"https://doi.org/10.1101/2025.03.03.25321546","citation_count":0,"is_preprint":true}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":29631,"output_tokens":8026,"usd":0.104641},"stage2":{"model":"claude-opus-4-6","input_tokens":11779,"output_tokens":3765,"usd":0.22953},"total_usd":0.334171,"stage1_batch_id":"msgbatch_011rkcQdVV1RaFq9XhcG6df6","stage2_batch_id":"msgbatch_01RzgrJafdF4EWHhj5mNi6dh","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 1998,\n      \"finding\": \"Brr2 (yeast ortholog of SNRNP200) unwinds the U4/U6 RNA duplex in an ATP hydrolysis-dependent manner; immunopurified Brr2 in a native U1/U2/U5/U4/U6 snRNP complex catalyzes U4/U6 base-pair disruption and release of free U4 and U6 snRNPs, and a helicase-domain mutation (brr2-1) abolishes this activity.\",\n      \"method\": \"Immunopurification of native snRNP complex, ATP hydrolysis assay, helicase-domain point mutant\",\n      \"journal\": \"Current biology : CB\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro reconstitution with native complex and active-site mutagenesis, foundational study\",\n      \"pmids\": [\"9705931\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"The human U5-200kD protein (SNRNP200/hBrr2) is the subunit of U5 snRNP responsible for ATP-dependent unwinding of U4/U6 RNA duplexes in vitro; activity was traced to the purified 200kD DEXH-box protein after high-salt depletion of U5-100kD from U5 snRNPs.\",\n      \"method\": \"In vitro U4/U6 RNA unwinding assay with purified HeLa U5 snRNPs; high-salt protein depletion; ion-exchange purification of U5-200kD to homogeneity\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro biochemical reconstitution with purified protein, replicated the yeast finding in human system\",\n      \"pmids\": [\"9539711\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"ATP-dependent Brr2-mediated dissociation of U4/U6 snRNAs in vitro is stimulated by the C-terminal region of the U5 snRNP protein Prp8 (Prp8-CTR); in contrast, Prp8-CTR simultaneously inhibits U4/U6-dependent ATPase activity; retinitis pigmentosa-linked prp8 alleles fail to stimulate Brr2 unwinding activity.\",\n      \"method\": \"In vitro U4/U6 unwinding and ATPase assays with purified Prp8 fragments; yeast genetics with RP alleles\",\n      \"journal\": \"Nature structural & molecular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — reconstituted in vitro with defined components, multiple orthogonal assays\",\n      \"pmids\": [\"19098916\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Brr2, Prp8, and the GTPase Snu114 are localized within distinct domains of the yeast tri-snRNP by electron microscopy: Brr2 occupies a 'head' domain, U4/U6 snRNP forms an 'arm' domain, and Prp8/Snu114 are central; the head and arm adopt variable relative positions suggesting dynamics during activation.\",\n      \"method\": \"Electron microscopy of genetically tagged tri-snRNP complexes; EM projection structure\",\n      \"journal\": \"Nature structural & molecular biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct EM localization of tagged proteins within native complex\",\n      \"pmids\": [\"18953335\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"Crystal structure of the second Sec63 domain of Brr2 reveals structural similarity to domains 4-5 of DNA helicase Hel308; together with sequence conservation in RecA-like domains, this defines two consecutive Hel308-like modules (Hel308-I and -II) in Brr2; the C-terminal Hel308-II module (Hel308-II) interacts with Prp8 and Snu114 in vitro and in vivo, and Prp8-CTR facilitates binding of the Brr2-Prp8 complex to U4/U6.\",\n      \"method\": \"Crystal structure determination; in vitro and in vivo interaction assays; mutagenesis coupled with U4/U6 unwinding assays\",\n      \"journal\": \"Nature structural & molecular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — crystal structure plus mutagenesis plus functional interaction assays\",\n      \"pmids\": [\"19525970\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"Crystal structures of the C-terminal Sec63 unit of yeast Brr2 reveal three domains, two of which resemble functional modules of the DNA helicase Hel308; rational mutagenesis and structural modeling show how RecA-like domains and the Sec63 unit form a functional entity mediating unidirectional and processive RNA duplex unwinding.\",\n      \"method\": \"Crystal structure determination; rational mutagenesis; splicing and U4/U6 di-snRNA unwinding assays\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — crystal structure with mutagenesis and functional assays\",\n      \"pmids\": [\"19716790\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"RP-linked mutations S1087L and R1090L in SNRNP200 reside in the ratchet helix of the first Sec63 domain and cause marked defects in U4/U6 snRNA unwinding without affecting U4/U6-U5 snRNP assembly, establishing that hBrr2's RNA unwinding activity is specifically impaired by these mutations.\",\n      \"method\": \"Yeast functional assays of analogous mutations (N1104L and R1107L in yeast Brr2p); U4/U6 unwinding assays; U4/U6-U5 tri-snRNP assembly assays\",\n      \"journal\": \"American journal of human genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — in vitro unwinding assays with defined point mutants, linked to disease mechanism\",\n      \"pmids\": [\"19878916\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Human Brr2 contains two ring-like helicase cassettes that intimately interact; only the N-terminal cassette harbors ATPase and helicase activity in isolation, while the C-terminal cassette binds ATP and strongly stimulates the N-terminal helicase; structural features suggest Brr2 loads onto an internal region of U4/U6 di-snRNA via the N-terminal cassette.\",\n      \"method\": \"Crystal structures; mutagenesis of intercassette interface and C-terminal ATP pocket; RNA-binding and ATPase assays; functional complementation\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — crystal structure plus mutagenesis plus multiple functional assays\",\n      \"pmids\": [\"23045696\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"The RNase H-like (RH) domain of Prp8 binds U4/U6 snRNA at single-stranded regions of U4 and U6 preceding U4/U6 stem I, and blocks Brr2's interaction with the same U4 single-stranded region, thereby inhibiting U4/U6 unwinding; cross-linking/mass spectrometry identifies the RH domain residues contacting U4/U6 snRNA.\",\n      \"method\": \"RNA binding assays; cross-linking coupled with mass spectrometry; U4/U6 unwinding assays with Prp8 RH domain\",\n      \"journal\": \"Genes & development\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — biochemical reconstitution with multiple orthogonal methods (CLIP-MS, RNA binding, unwinding)\",\n      \"pmids\": [\"23124066\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"The C-terminal tail of Prp8 (Jab1/MPN domain) inserts into Brr2's RNA-binding tunnel, directly competing with RNA substrate binding and thereby reversibly inhibiting Brr2's RNA-binding, ATPase, and U4/U6 unwinding activities; RP-linked Prp8 mutations in the C-terminal tail result in inefficient Brr2 repression.\",\n      \"method\": \"Crystal structure of Brr2–Prp8 C-terminal tail complex; ATPase assays; RNA-binding assays; U4/U6 unwinding assays\",\n      \"journal\": \"Science (New York, N.Y.)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — crystal structure plus multiple biochemical assays, mechanism directly demonstrated\",\n      \"pmids\": [\"23704370\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"The Jab1/MPN domain of Prp8 binds exclusively to the N-terminal helicase cassette of yeast Brr2 and stimulates its activity; RP-causing mutations in the Prp8 Jab1/MPN domain are at or near the Brr2 interface; in U5 snRNP biogenesis, Brr2 replaces the assembly factor Aar2 after nuclear import, explaining their mutual exclusivity.\",\n      \"method\": \"Crystal structure of yeast Brr2–Prp8 Jab1/MPN complex; mutagenesis; biochemical competition assays\",\n      \"journal\": \"Structure (London, England : 1993)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — crystal structure with mutagenesis and functional biochemistry\",\n      \"pmids\": [\"23727230\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"RP-linked mutations S1087L and R1090L in human BRR2 (SNRNP200) enhance cryptic splice-site recognition and impair proper 5'-splice-site selection; depletion of endogenous BRR2 enhanced usage of a β-globin cryptic splice site, which was restored by wild-type but not RP mutant BRR2.\",\n      \"method\": \"Stable expression of BAC-recombineered BRR2 mutants in human cell culture; RT-PCR splice-site usage assays; BRR2 knockdown-rescue experiments\",\n      \"journal\": \"Human mutation\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — clean KD/KO with defined cellular phenotype plus mutant rescue in human cells\",\n      \"pmids\": [\"24302620\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Sad1 counteracts Brr2-mediated ATP-dependent dissociation of the U4/U6•U5 tri-snRNP, maintaining tri-snRNP integrity; in the absence of Sad1, Brr2 drives tri-snRNP dissociation into U5 and U4/U6 snRNPs upon ATP hydrolysis.\",\n      \"method\": \"In vitro tri-snRNP dissociation assay with ATP; yeast genetics; sedimentation analyses\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — in vitro reconstitution with purified components plus genetic validation\",\n      \"pmids\": [\"24190974\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"U5 snRNA internal loop 1 (IL1) serves as a binding platform for Prp8, Snu114, and Brr2 during U5 snRNP assembly; mutations in both sides of IL1 reduce association of all three proteins with U5 snRNA, and genetic interactions between brr2 alleles and U5 IL1 mutants reveal synthetic lethality.\",\n      \"method\": \"Yeast in vivo mutagenesis of U5 snRNA; co-immunoprecipitation; genetic synthetic lethality screening\",\n      \"journal\": \"Journal of cellular biochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal in vivo interaction data plus epistasis\",\n      \"pmids\": [\"23857713\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"The N-terminal region (~500 residues) of Brr2 encompasses two folded domains and adjacent linear elements that clamp and interconnect the helicase cassettes; it autoinhibits Brr2 via substrate competition and conformational clamping, and is required for stable Brr2 association with tri-snRNP and retention of U5 and U6 snRNAs during spliceosome activation in vivo.\",\n      \"method\": \"Crystal structure of full-length Brr2 with Prp8 Jab1/MPN domain; cross-linking/mass spectrometry; yeast growth and splicing assays with N-terminal truncations; RNA-binding, ATPase, and helicase assays\",\n      \"journal\": \"Genes & development\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — crystal structure plus cross-linking MS plus multiple functional assays in vivo and in vitro\",\n      \"pmids\": [\"26637280\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"The N-terminal region of Brr2 contains a noncanonical PWI-like domain that does not bind nucleic acids but instead interacts with other spliceosomal proteins including the Prp19 complex protein SPF27, supporting a role of the N-terminal region as a protein-protein interaction platform.\",\n      \"method\": \"Crystal structure of C. thermophilum Brr2 PWI-like domain; CD spectroscopy; yeast two-hybrid screen against human spliceosomal proteins; band-shift assays\",\n      \"journal\": \"Acta crystallographica. Section D, Biological crystallography\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1-2 — crystal structure plus interaction screen, but interaction not yet functionally validated\",\n      \"pmids\": [\"25849387\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"The N-terminal domain of Brr2 (first ~120 residues) is required for spliceosomal activation beyond U4/U6 unwinding, specifically for retaining U5 and U6 snRNPs during activation; Brr2-Δ120 integrates into tri-snRNP and B complex but fails to maintain U5/U6 during Bact complex formation.\",\n      \"method\": \"Yeast genetics; yeast growth and splicing assays with N-terminal deletions; spliceosomal complex purification and snRNA composition analysis\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — loss-of-function with defined in vivo splicing phenotype and complex composition analysis\",\n      \"pmids\": [\"25670679\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"During Brr2-mediated U4/U6 di-snRNP disruption, Brr2 translocates only a limited distance on the U4 snRNA strand; completion of unwinding requires U6 snRNA to adopt an alternative conformation, releasing Prp3 from U4/U6 di-snRNA while leaving Prp31 and Snu13 bound to U4 snRNA as an intact particle; Brr2 thus strips U6 of all precatalytic binding partners via a substrate-assisted mechanism.\",\n      \"method\": \"Recombinant in vitro Brr2-mediated U4/U6 di-snRNP disruption system; sequential protein addition assays; mutational analysis of U4/U6 di-snRNA conformation\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — reconstituted system with defined recombinant components and mechanistic dissection\",\n      \"pmids\": [\"27354531\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"SNRNP200 relocalizes into TBK1-containing cytoplasmic structures upon viral infection; its N-terminal Sec63 domain (Sec63-1) binds viral RNA and interacts with TBK1, promoting IRF3 activation and antiviral IFN-β production; the RP-linked S1087L mutant fails to relocalize and cannot rescue antiviral response in knockdown cells.\",\n      \"method\": \"Knockdown and rescue assays; co-immunoprecipitation with TBK1; RNA binding assays; live-cell imaging of localization upon infection; IFN-β production assays in patient PBMCs\",\n      \"journal\": \"PLoS pathogens\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — multiple orthogonal methods but functional rescue is partial and novel non-splicing role\",\n      \"pmids\": [\"27454487\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"RP mutations in the ratchet helix of Brr2 (S1087L, R1090L and analogues) exhibit a gradient of weakened RNA binding, reduced helicase activity, and reduced ATPase activity; the Prp8 Jab1/MPN domain increases wild-type Brr2 RNA binding and ATPase activity but does not differentially rescue RP mutants; RP mutant Brr2 proteins capable of RNA binding cannot fully unwind even short duplexes, suggesting impaired translocation.\",\n      \"method\": \"In vitro biochemical assays (RNA binding, ATPase, helicase) with purified RP-mutant Brr2 proteins; Prp8 Jab1 domain stimulation assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — systematic in vitro characterization with purified mutant proteins and multiple assays\",\n      \"pmids\": [\"27072132\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Brr2 autoinhibition (via N-terminal region) and Jab1-mediated inhibition (via Prp8 C-terminal tail insertion into RNA-binding tunnel) act in concert; the N-terminal region influences how the Jab1 tail interacts at the RNA-binding tunnel; N-terminal region specifically interferes with accommodation of double-stranded RNA, while the Jab1 tail interferes with single-stranded RNA, and regulation from the N-terminal region requires the inactive C-terminal helicase cassette.\",\n      \"method\": \"Crystal structures of S. cerevisiae and C. thermophilum Brr2-Jab1 complexes; systematic RNA binding and unwinding studies with truncation and mutant variants\",\n      \"journal\": \"Cell cycle (Georgetown, Tex.)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — crystal structures from two organisms plus systematic biochemical dissection\",\n      \"pmids\": [\"27880071\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"FBP21 uses an intrinsically disordered C-terminal region to bind the C-terminal Sec63 unit of Brr2, allosterically inhibiting Brr2 helicase activity; direct interaction of FBP21 with U4/U6 di-snRNA further reduces the pool of unwound U4/U6 di-snRNA.\",\n      \"method\": \"Yeast two-hybrid; analytical SEC; surface plasmon resonance; peptide SPOT analysis; RNA binding and unwinding assays\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal biochemical methods establishing binding site and functional consequence\",\n      \"pmids\": [\"28838205\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Two distinct small-molecule inhibitors of Brr2 were identified: one binds an allosteric site between the C-terminal and N-terminal helicase cassettes and is Brr2-selective, and another binds the RNA-binding site inside the N-terminal cassette; co-crystal structures revealed binding modes.\",\n      \"method\": \"HTS ATPase assay; co-crystal structures; helicase inhibition assays; selectivity profiling\",\n      \"journal\": \"Journal of medicinal chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — co-crystal structures with functional validation\",\n      \"pmids\": [\"28586220\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Ntr2, an intrinsically disordered yeast spliceosomal disassembly factor, binds via its N-terminal region to the C-terminal helicase unit of Brr2 and downregulates Brr2 helicase activity in vitro by modulating the fraction of helicase molecules productively bound to RNA substrate.\",\n      \"method\": \"CD spectroscopy; DLS; NMR spectroscopy; peptide SPOT analyses; analytical SEC; SPR; RNA binding and unwinding assays\",\n      \"journal\": \"Biophysical journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — multiple biophysical methods identifying binding site plus functional consequence in vitro\",\n      \"pmids\": [\"29490241\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"The inactive C-terminal cassette of BRR2 can both stimulate and inhibit the RNA-unwinding activity of the N-terminal cassette depending on the relative orientation of the two cassettes; engineered disulfide bridges locking cassettes in two different orientations had opposite effects (one enhancing, one inhibiting) on RNA unwinding and ATP hydrolysis.\",\n      \"method\": \"Crystal structure of BRR2 with Prp8 activating domain at 2.4 Å; engineered disulfide bridges; RNA unwinding and ATPase assays; comparison with spliceosomal cryo-EM structures\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — crystal structure plus engineered constraints with direct functional readouts\",\n      \"pmids\": [\"31914407\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Both BRR2 cassettes bind adenine nucleotides with high specificity; the inactive C-terminal cassette binds ADP >100-fold more tightly than the active N-terminal cassette; abrogation of nucleotide binding at the C-terminal cassette reduces nucleotide affinity at the N-terminal cassette 70 Å away via long-range allosteric communication mediated primarily across the intercassette interface.\",\n      \"method\": \"Biophysical nucleotide binding assays; mutations at intercassette surfaces; molecular dynamics simulations\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — biophysical assays plus computational validation with mutagenesis confirming allosteric pathway\",\n      \"pmids\": [\"34048711\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"C9ORF78 tightly interacts with BRR2 at a multi-factor trafficking site on the C-terminal helicase cassette, occupying a binding surface that FBP21 also uses in a mutually exclusive manner; cryo-EM structures reveal how C9ORF78 and FBP21 wrap around the C-terminal helicase cassette; C9ORF78 knockdown leads to alternative NAGNAG 3'-splice site usage and BRR2-dependent exon skipping.\",\n      \"method\": \"Cryo-EM structures; in vitro binding assays; affinity purification/mass spectrometry; RNA UV-crosslinking; knockdown with alternative splicing analysis\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — cryo-EM structures plus multiple functional assays establishing regulatory role\",\n      \"pmids\": [\"35241646\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"A C. elegans forward genetic screen identified a suppressor allele in SNRNP200/BRR2 (N18K at the unstructured N-terminus) that suppresses 5'-splice-site identity defects, revealing a conserved role for SNRNP200 in maintaining 5'-splice-site identity during spliceosome assembly.\",\n      \"method\": \"Forward genetic screen in C. elegans; mRNA-seq; double-mutant analysis; mapping of suppressor residues on cryo-EM spliceosome structures\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — genetic epistasis screen with functional mRNA-seq validation in a relevant model organism\",\n      \"pmids\": [\"36321655\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Glucose-induced acetylation of SNRNP200 at K1610 prevents its proteasomal degradation; stabilized SNRNP200 then facilitates splicing of metabolic enzyme-encoding pre-mRNAs (GAPDH, ALDOA, GSS), increasing lactic acid and glutathione production in triple-negative breast cancer.\",\n      \"method\": \"Mass spectrometry identification of acetylation site; proteasome inhibition/ubiquitination assays; splicing assays; metabolic readouts\",\n      \"journal\": \"Cell discovery\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — identification of PTM with defined functional consequence, single lab study\",\n      \"pmids\": [\"39285160\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"RP-linked mutations S1087L and R1090L in SNRNP200 broaden its binding profile on U4 snRNA upstream of U4/U6 stem I as measured by iCLIP, indicating impaired snRNA unwinding activity; this was confirmed by FRAP measurements and in vitro helicase activity assays comparing mutant and wild-type protein.\",\n      \"method\": \"iCLIP in HeLa and RPE cells; FRAP; in vitro helicase activity assays\",\n      \"journal\": \"Cellular and molecular life sciences : CMLS\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — multiple orthogonal methods (iCLIP, FRAP, in vitro helicase) confirming mechanism of RP mutations\",\n      \"pmids\": [\"40045025\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Y4 RNA fragment (YF1) binds to SNRNP200 and reduces its ubiquitination, stabilizing SNRNP200, which in turn enhances IL-10 pre-mRNA splicing in macrophages; this effect is reversed by a specific SNRNP200 inhibitor (Brr2-IN-3).\",\n      \"method\": \"Co-immunoprecipitation; ubiquitination assays; mRNA splicing ratio assays; pharmacological inhibition with Brr2-IN-3\",\n      \"journal\": \"Molecular therapy : the journal of the American Society of Gene Therapy\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — single lab, Co-IP and functional assay with inhibitor validation\",\n      \"pmids\": [\"39935176\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"BRR2/Brr2 functions as an evolutionarily conserved ciR-loop (circRNA-associated R-loop) repressor with dual roles: inhibiting circRNA generation and resolving ciR-loops; loss of Brr2 leads to ciR-loop accumulation, antisense transcription, premature transcription termination, DNA damage, and defects in DNA replication and cell division.\",\n      \"method\": \"Loss-of-function genetics; R-loop detection assays; RNA-seq; DNA damage assays; cell cycle analysis\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — defined loss-of-function phenotypes with multiple readouts, novel role outside splicing\",\n      \"pmids\": [\"41093835\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Dominant-negative mutation in the helicase domain I of human U5-200kD (SNRNP200) expressed in HEK293 cells causes delayed exit from G2/M phase due to splicing defects; shRNA-mediated knockdown of U5-200kD causes S-phase arrest.\",\n      \"method\": \"Dominant-negative expression in ecdysone-inducible system; shRNA knockdown; cell cycle analysis; RT-PCR splicing assays\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — loss-of-function and dominant-negative with defined cell cycle phenotypes in human cells\",\n      \"pmids\": [\"23637979\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"SNRNP200 (hBrr2) is a Ski2-like DEXH-box RNA helicase and permanent U5 snRNP component that drives spliceosome activation by using ATP-driven translocation along U4 snRNA to unwind the U4/U6 duplex, a process regulated through multiple cis-mechanisms (autoinhibitory N-terminal region, stimulatory but inactive C-terminal helicase cassette, and long-range allosteric communication between cassettes) and trans-mechanisms (inhibition or activation by consecutive RNase H-like and Jab1/MPN-like domains of Prp8 inserting into Brr2's RNA-binding tunnel, inhibition by FBP21, Ntr2, and C9ORF78 at the C-terminal cassette), with retinitis pigmentosa-linked ratchet-helix mutations specifically impairing RNA unwinding and translocation without disrupting snRNP assembly.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"SNRNP200 (hBrr2) is a Ski2-like DEXH-box RNA helicase and permanent U5 snRNP component that drives spliceosome activation by ATP-dependent unwinding of the U4/U6 snRNA duplex, a prerequisite for catalytic core formation [PMID:9705931, PMID:9539711]. The enzyme contains two tandem Hel308-like helicase cassettes: only the N-terminal cassette is catalytically active, while the C-terminal cassette binds nucleotides and allosterically modulates unwinding through long-range intercassette communication and orientation-dependent stimulation or inhibition [PMID:23045696, PMID:34048711, PMID:31914407]. Multiple regulatory mechanisms converge on Brr2, including autoinhibition by its N-terminal region, inhibition by insertion of the Prp8 Jab1/MPN C-terminal tail into the RNA-binding tunnel, competition by the Prp8 RNase H domain for the U4 snRNA loading site, and modulation by trans-acting factors (FBP21, Ntr2, C9ORF78) that bind the C-terminal cassette [PMID:26637280, PMID:23704370, PMID:23124066, PMID:28838205, PMID:35241646]. Retinitis pigmentosa-causing missense mutations in the ratchet helix (S1087L, R1090L) specifically impair RNA translocation and unwinding without disrupting tri-snRNP assembly, leading to aberrant splice-site selection [PMID:19878916, PMID:27072132, PMID:24302620].\",\n  \"teleology\": [\n    {\n      \"year\": 1998,\n      \"claim\": \"Identification of the U4/U6 unwinding activity resolved which snRNP subunit drives spliceosome activation: both yeast Brr2 and human U5-200kD were shown to catalyze ATP-dependent U4/U6 duplex disruption, establishing the core enzymatic function of SNRNP200.\",\n      \"evidence\": \"Immunopurified native snRNP complex unwinding assays with helicase-dead mutant (yeast); purified U5-200kD from HeLa U5 snRNPs (human)\",\n      \"pmids\": [\"9705931\", \"9539711\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Substrate specificity and loading mechanism on U4/U6 not yet defined\", \"Role of other U5 snRNP proteins in regulating unwinding unknown\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Discovery that Prp8's C-terminal region simultaneously stimulates U4/U6 unwinding while inhibiting ATPase activity established that Brr2 is subject to complex trans-regulation by its stable binding partner, and linked retinitis pigmentosa-associated Prp8 mutations to defective Brr2 regulation.\",\n      \"evidence\": \"In vitro unwinding and ATPase assays with purified Prp8 fragments; RP allele testing in yeast\",\n      \"pmids\": [\"19098916\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular basis of dual stimulation/inhibition not structurally resolved\", \"How Prp8 regulation is switched on/off during the splicing cycle unknown\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Crystal structures of Brr2 Sec63 domains revealed a dual Hel308-like module architecture and showed that the C-terminal module mediates Prp8/Snu114 interaction, while RP mutations S1087L and R1090L in the ratchet helix of the first Sec63 domain specifically impair U4/U6 unwinding without disrupting tri-snRNP assembly, pinpointing the disease mechanism.\",\n      \"evidence\": \"Crystal structures; rational mutagenesis; U4/U6 unwinding and tri-snRNP assembly assays in yeast and human systems\",\n      \"pmids\": [\"19525970\", \"19716790\", \"19878916\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Full-length Brr2 structure not yet available\", \"Translocation mechanism along U4 snRNA not defined\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Structural and functional analysis of full dual-cassette Brr2 revealed that only the N-terminal cassette is catalytically active while the C-terminal cassette acts as a regulatory cofactor, and separately showed that Prp8's RNase H domain blocks Brr2 loading onto U4 snRNA, defining two layers of Prp8-mediated inhibition.\",\n      \"evidence\": \"Crystal structures of dual-cassette Brr2; mutagenesis of intercassette interface and ATP pocket; cross-linking/MS mapping of Prp8 RH–U4/U6 contacts; RNA binding and unwinding assays\",\n      \"pmids\": [\"23045696\", \"23124066\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How the two Prp8 inhibitory mechanisms (RH domain and Jab1 tail) are coordinated temporally unknown\", \"Nucleotide occupancy states of C-terminal cassette during splicing not determined\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Crystal structures of the Prp8 Jab1/MPN domain bound to Brr2 revealed a direct inhibitory mechanism—the Jab1 C-terminal tail inserts into Brr2's RNA-binding tunnel, competing with substrate—and showed that RP-linked Prp8 mutations weaken this inhibition; concurrently, Sad1 was shown to counteract premature Brr2-mediated tri-snRNP disruption, and RP Brr2 mutations were found to alter splice-site selection in human cells.\",\n      \"evidence\": \"Co-crystal structures of Brr2–Jab1 (human and yeast); ATPase/unwinding assays; tri-snRNP dissociation assays; knockdown-rescue with RP mutants in human cells\",\n      \"pmids\": [\"23704370\", \"23727230\", \"24190974\", \"24302620\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism by which Jab1 tail is withdrawn to activate Brr2 in the spliceosome unknown\", \"Whether Sad1 directly contacts Brr2 or acts indirectly not resolved\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"The ~500-residue N-terminal region of Brr2 was shown to act as a cis-autoinhibitory element that clamps the two helicase cassettes, competes with dsRNA substrate, and is required beyond U4/U6 unwinding for retaining U5 and U6 snRNAs during spliceosome activation.\",\n      \"evidence\": \"Crystal structure of full-length Brr2–Jab1 complex; N-terminal truncation mutants assayed for RNA binding, ATPase, helicase activity, and spliceosomal complex composition in vivo\",\n      \"pmids\": [\"26637280\", \"25670679\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How N-terminal autoinhibition is relieved during the B-to-Bact transition not determined\", \"Identity of signals triggering relief of autoinhibition unknown\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Mechanistic dissection established that Brr2 translocates only a limited distance on U4 snRNA and relies on U6 snRNA conformational rearrangement (substrate-assisted unwinding) to complete U4/U6 disruption; separately, RP ratchet-helix mutations were shown to impair translocation specifically, and dual autoinhibition by the N-terminal region and Jab1 tail was shown to target dsRNA vs ssRNA accommodation differentially.\",\n      \"evidence\": \"Reconstituted U4/U6 di-snRNP disruption with recombinant components; systematic biochemical characterization of RP mutants; crystal structures from two organisms with truncation/mutant RNA binding studies\",\n      \"pmids\": [\"27454531\", \"27072132\", \"27880071\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Step-size and processivity of Brr2 translocation not quantified\", \"Whether substrate-assisted mechanism operates in the context of the full spliceosome not tested\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Trans-regulators binding the C-terminal cassette were identified: FBP21 uses an intrinsically disordered region to allosterically inhibit Brr2, while small-molecule inhibitors targeting both allosteric and active sites were co-crystallized, validating druggability of the intercassette interface.\",\n      \"evidence\": \"SPR, analytical SEC, peptide SPOT analysis, unwinding assays (FBP21); HTS and co-crystal structures (inhibitors)\",\n      \"pmids\": [\"28838205\", \"28586220\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In vivo functional consequence of FBP21-mediated inhibition not demonstrated\", \"Selectivity and efficacy of inhibitors in splicing-dependent cellular assays not shown\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Engineered disulfide bridges locking the two cassettes in distinct relative orientations demonstrated that intercassette rotation can either stimulate or inhibit unwinding, establishing that the C-terminal cassette acts as a conformational switch rather than a simple stimulator.\",\n      \"evidence\": \"Crystal structure of BRR2–Prp8 activating domain; disulfide-locked variants; ATPase and helicase assays\",\n      \"pmids\": [\"31914407\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Which cassette orientation is adopted at each spliceosomal stage not mapped\", \"Whether intercassette rotation is actively driven or passive unknown\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Nucleotide-binding measurements revealed that the C-terminal cassette binds ADP >100-fold more tightly than the N-terminal cassette, and long-range allosteric communication across the intercassette interface was demonstrated: disrupting nucleotide binding at the C-terminal cassette reduced affinity at the N-terminal cassette 70 Å away.\",\n      \"evidence\": \"Biophysical nucleotide binding assays; intercassette interface mutations; molecular dynamics simulations\",\n      \"pmids\": [\"34048711\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Identity of the allosteric pathway residues at atomic resolution incomplete\", \"Whether ADP/ATP exchange at the C-terminal cassette occurs during the splicing cycle unknown\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Cryo-EM structures of C9ORF78 and FBP21 bound to Brr2's C-terminal cassette identified a shared, mutually exclusive regulatory site ('multi-factor trafficking site'), and C9ORF78 knockdown produced BRR2-dependent splicing changes including alternative 3'-splice-site usage, establishing the C-terminal cassette as a regulatory hub for sequential trans-factor engagement.\",\n      \"evidence\": \"Cryo-EM structures; affinity purification/MS; RNA UV-crosslinking; knockdown with splicing analysis\",\n      \"pmids\": [\"35241646\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Order of factor exchange at the C-terminal cassette during splicing cycle not resolved\", \"Whether additional factors share this binding surface unknown\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"iCLIP mapping of RP mutant Brr2 in living cells showed broadened binding on U4 snRNA upstream of stem I, directly demonstrating impaired translocation in vivo; separately, Brr2 was identified as a repressor of circRNA-associated R-loops (ciR-loops), with loss of function causing R-loop accumulation, DNA damage, and replication defects.\",\n      \"evidence\": \"iCLIP in HeLa/RPE cells plus FRAP and in vitro helicase assays (RP mutations); loss-of-function genetics with R-loop detection and DNA damage assays (ciR-loop role)\",\n      \"pmids\": [\"40045025\", \"41093835\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether the ciR-loop repression function requires Brr2's helicase activity or is independent unknown\", \"Cell-type specificity of RP mutant translocation defects not fully explored\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How the multiple inhibitory and stimulatory inputs on Brr2 (N-terminal autoinhibition, Prp8 RH domain, Prp8 Jab1 tail, C-terminal cassette orientation, and trans-factors at the C-terminal cassette) are temporally coordinated across spliceosomal stages to achieve precisely timed activation and subsequent disassembly remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Time-resolved single-molecule studies of Brr2 regulation during a complete splicing cycle are lacking\", \"Whether Brr2's non-splicing roles (innate immunity, ciR-loop resolution) share the same regulatory architecture is unknown\", \"Structural basis for how the N-terminal PWI-like domain engages downstream spliceosomal factors during activation not determined\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140657\", \"supporting_discovery_ids\": [0, 1, 7, 19, 25]},\n      {\"term_id\": \"GO:0003723\", \"supporting_discovery_ids\": [0, 1, 8, 17, 29]},\n      {\"term_id\": \"GO:0140098\", \"supporting_discovery_ids\": [0, 1, 7, 17, 19]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [3, 13, 16]},\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [18]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-8953854\", \"supporting_discovery_ids\": [0, 1, 6, 7, 11, 17, 27, 28, 29]},\n      {\"term_id\": \"R-HSA-1643685\", \"supporting_discovery_ids\": [6, 11, 19, 29]}\n    ],\n    \"complexes\": [\n      \"U5 snRNP\",\n      \"U4/U6.U5 tri-snRNP\"\n    ],\n    \"partners\": [\n      \"PRPF8\",\n      \"SNU114\",\n      \"FBP21\",\n      \"C9ORF78\",\n      \"NTR2\",\n      \"SAD1\",\n      \"SPF27\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}