{"gene":"SUPT5H","run_date":"2026-06-10T10:51:54","timeline":{"discoveries":[{"year":1998,"finding":"DSIF, the human transcription elongation factor composed of SPT5 (p160/SUPT5H) and SPT4 (p14), was purified from HeLa nuclear extracts and shown to cause RNA polymerase II pausing in conjunction with DRB. In vitro, DSIF also stimulates elongation rate at limiting NTP concentrations, demonstrating dual positive and negative roles in Pol II processivity.","method":"Biochemical purification from HeLa extracts, in vitro transcription assay, cDNA cloning, recombinant protein complementation","journal":"Genes & development","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro reconstitution with purified factor, multiple assays, replicated in parallel yeast study (PMID:9450930)","pmids":["9450929"],"is_preprint":false},{"year":1998,"finding":"Yeast Spt5 physically associates with RNA polymerase II in vivo (co-immunoprecipitation), and genetic suppression of conditional spt5 mutations by mutations in the two largest Pol II subunits (one of which causes an elongation defect) places Spt5 in the transcription elongation machinery. Spt4 and Spt5 form a tight complex that does not contain Spt6.","method":"Co-immunoprecipitation, genetic epistasis (allele-specific suppression by Pol II mutants), conditional mutant phenotyping","journal":"Genes & development","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal genetic and biochemical evidence, replicated across two simultaneous publications","pmids":["9450930"],"is_preprint":false},{"year":1991,"finding":"Yeast SPT5 is an essential nuclear protein; null mutation is lethal, indicating requirement for normal transcription of many genes. The protein localizes to the nucleus by indirect immunofluorescence of an SPT5-β-galactosidase fusion.","method":"Null mutant construction, indirect immunofluorescence of fusion protein, SPT5 cloning and sequencing","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — direct genetic essentiality plus subcellular localization experiment, replicated in subsequent studies","pmids":["1840633"],"is_preprint":false},{"year":2000,"finding":"SPT5 domains required for transcriptional regulation were defined: the SPT4-binding domain, the RNA Pol II-binding domain, and the C-terminal repeat region CTR1 are all required for DRB-mediated transcriptional repression and Tat-mediated activation in vitro. The CTR1 domain is a substrate for P-TEFb (CDK9/cyclin T1) phosphorylation.","method":"Domain deletion/truncation analysis, in vitro transcription assay, phosphorylation assay with recombinant P-TEFb","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro transcription assay with mutagenesis and direct phosphorylation assay, single lab with multiple orthogonal methods","pmids":["10757782"],"is_preprint":false},{"year":2000,"finding":"Drosophila Spt5 colocalizes with actively elongating (phosphorylated) RNA Pol II but not with non-elongating Pol II at polytene chromosome loci, and is recruited to heat shock gene promoters before heat shock and to 5' and 3' ends of genes after heat shock induction, consistent with roles in promoter-proximal pausing and elongation.","method":"Immunofluorescence on polytene chromosomes, chromatin immunoprecipitation (ChIP)","journal":"Genes & development","confidence":"High","confidence_rationale":"Tier 2 / Strong — direct localization with functional consequence, two independent Drosophila studies published simultaneously","pmids":["11040217","11040216"],"is_preprint":false},{"year":2003,"finding":"SPT5 is specifically methylated by protein arginine methyltransferases PRMT1 and PRMT5. Specific arginine residues in SPT5 are methylated by these enzymes, and methylation regulates SPT5 interaction with RNA polymerase II, its promoter association, and its transcriptional elongation properties.","method":"Biochemical co-association assay, in vitro methylation assay, mutagenesis of arginine residues, co-immunoprecipitation with Pol II","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro methylation assay plus mutagenesis and interaction mapping, single lab with multiple orthogonal methods","pmids":["12718890"],"is_preprint":false},{"year":2003,"finding":"Yeast Spt5 co-immunopurifies with general elongation factors TFIIF and TFIIS, chromatin regulators Spt6 and FACT, and mRNA capping enzyme and cap methyltransferase. spt4 and spt5 mutations genetically interact with capping enzyme gene mutations and lead to accumulation of unspliced pre-mRNA, revealing roles in pre-mRNA processing.","method":"Co-immunopurification/mass spectrometry, genetic interaction analysis, pre-mRNA accumulation assay","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 2 / Moderate — reciprocal co-IP with MS plus genetic interactions, single lab with multiple orthogonal methods","pmids":["12556496"],"is_preprint":false},{"year":2002,"finding":"Spt5 is recruited to the HIV-1 transcription complex shortly after initiation. CDK9 activation induces hyperphosphorylation of Spt5 in parallel with Pol II CTD phosphorylation. Spt5-depleted extracts show Spt5 is not required for early elongation or Tat-dependent kinase activation, but is required in late elongation to prevent premature dissociation of RNA from the transcription complex at terminator sequences and to reduce polymerase pausing at arrest sites.","method":"In vitro three-stage transcription assay, immunodepletion, chase experiments with Spt5-depleted extracts","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro reconstitution with immunodepletion, multiple assays defining stage-specific function, single lab","pmids":["11809800"],"is_preprint":false},{"year":2002,"finding":"Fission yeast Spt5 C-terminal domain (CTD), composed of nonapeptide repeats (TPAWNSGSK), is necessary and sufficient for binding to mRNA capping enzymes Pct1 (triphosphatase) and Pce1 (guanylyltransferase), both in two-hybrid and in vitro binding assays. Spt5 is essential in S. pombe and interacts with Spt4 via a central domain distinct from the CTD.","method":"Two-hybrid assay, in vitro binding assay with CTD truncations, genetic complementation","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro binding assay plus two-hybrid, domain mapping with multiple truncations, single lab","pmids":["11893740"],"is_preprint":false},{"year":2009,"finding":"The yeast Bur1 kinase directly phosphorylates the Spt5 C-terminal repeat domain (CTD) both in vivo and in isolated elongation complexes in vitro. Deletion of the Spt5 CTD or mutation of Spt5 serines targeted by Bur1 reduces PAF complex recruitment, decreases histone H3K4 trimethylation, and reduces Pol II CTD Ser-2 phosphorylation.","method":"Chemical genetics (analog-sensitive kinase), in vitro kinase assay with isolated elongation complexes, ChIP, histone modification analysis","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 1 / Moderate — chemical genetics plus in vitro kinase assay and ChIP, multiple orthogonal readouts, single lab","pmids":["19581288"],"is_preprint":false},{"year":2009,"finding":"BUR kinase phosphorylates the Spt5 CTR in vivo and in vitro, and the Spt5 CTR is required for PAF complex recruitment, histone H2B K123 monoubiquitination, and histone H3 K4/K36 trimethylation during transcription elongation.","method":"In vitro kinase assay, ChIP, histone modification western blot, genetic deletion analysis","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro kinase assay plus ChIP and genetic analysis, multiple chromatin modification readouts, single lab","pmids":["19365074"],"is_preprint":false},{"year":2013,"finding":"Crystal structure of human Rtf1 Plus3 domain in complex with a phosphorylated Spt5 repeat reveals that Spt5 binding is mediated by a phosphothreonine recognition interface and hydrophobic contacts. Mutations disrupting this interface diminish Spt5 binding in vitro and Rtf1 chromatin localization in vivo, establishing the molecular basis for Paf1C recruitment by phosphorylated Spt5.","method":"X-ray crystallography, in vitro binding assay, ChIP (chromatin localization)","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 / Strong — crystal structure plus in vitro binding mutagenesis plus in vivo chromatin localization, multiple orthogonal methods","pmids":["24101474"],"is_preprint":false},{"year":2008,"finding":"Crystal structure of yeast Spt4 bound to the NGN domain of Spt5 reveals an acid-dipole interaction governing Spt4-Spt5 binding. Mutations disrupting this interaction disrupt the complex. The archaeal Spt4-Spt5 homologs also form a complex, and Spt4 is positioned to maintain the functional conformation of KOW domains in Spt5.","method":"X-ray crystallography, mutagenesis of interface residues, archaeal complex reconstitution","journal":"Structure","confidence":"High","confidence_rationale":"Tier 1 / Strong — crystal structure plus mutagenesis validation, replicated in archaeal system, single study with multiple orthogonal methods","pmids":["19000817"],"is_preprint":false},{"year":2019,"finding":"PNUTS-PP1 phosphatase dephosphorylates Spt5 downstream of poly(A) sites, causing RNA Pol II deceleration from >2 kb/min to <1 kb/min. This deceleration is required for transcription termination by allowing Xrn2 to catch and torpedo Pol II ('sitting duck torpedo' mechanism). Disruption of PP1 binding (PNUTS W401A) causes genome-wide transcription acceleration and Spt5 hyper-phosphorylation.","method":"Genome-wide elongation rate measurement (TT-seq/metabolic labeling), ChIP-seq, mutant cell lines, PP1-binding mutation","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 2 / Strong — genome-wide functional assay with separation-of-function mutation and defined mechanistic readout, multiple orthogonal approaches","pmids":["31677974"],"is_preprint":false},{"year":2019,"finding":"MYC directly binds SPT5 and recruits SPT5 to promoters, enabling CDK7-dependent transfer of SPT5 onto Pol II to promote fast and processive transcription elongation. At oncogenic MYC levels, SPT5 is sequestered into non-functional complexes decreasing expression of growth-suppressive genes.","method":"Mass spectrometry of MYC and Pol II complexes, co-immunoprecipitation, ChIP-seq, elongation rate measurements","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 2 / Moderate — reciprocal Co-IP, MS, ChIP-seq and functional elongation assays, single lab with multiple orthogonal methods","pmids":["30928206"],"is_preprint":false},{"year":2021,"finding":"Acute depletion of SPT5 triggers ubiquitination and proteasomal degradation of the core Pol II subunit RPB1 specifically at promoter-proximal regions, mediated by E3 ligase Cullin 3, unfoldase VCP/p97, and a CDK9 kinase complex. This demonstrates that SPT5 stabilizes Pol II at promoter-proximal regions and is required for Pol II release into gene bodies.","method":"Auxin-inducible degron depletion, ubiquitination assay, proteasome inhibitor rescue, genetic complementation in yeast (evolutionary conservation), ChIP","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 2 / Strong — acute inducible depletion with multiple mechanistic rescue experiments, evolutionary conservation shown, multiple orthogonal methods","pmids":["34480849"],"is_preprint":false},{"year":2021,"finding":"Rapid SPT5 depletion causes pronounced reduction of paused Pol II at both promoters and enhancers, distinct from NELF depletion; impairs transcription activation; alters enhancer chromatin landscape; and causes Pol II processivity defects in gene bodies. Phosphorylation of SPT5 linker Ser666 by P-TEFb promotes pause release; this is antagonized by Integrator-PP2A (INTAC) targeting SPT5 and Pol II. SPT5 C-terminal region phosphorylation links to 3' end termination.","method":"Rapid degradation (dTAG system), ChIP-seq, PRO-seq, ATAC-seq, phospho-mutant analysis","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 2 / Strong — rapid depletion system with genome-wide and phospho-mutant analysis across multiple chromatin and transcriptional readouts, multiple orthogonal methods","pmids":["34534457"],"is_preprint":false},{"year":2010,"finding":"Spt5 interacts in vivo with the elongating form of RNA Pol II, and mutations in SPT4 or SPT5 reduce cotranscriptional recruitment of the RNA-binding protein She2p to the ASH1 gene, disrupting ASH1 mRNA localization to the bud tip and Ash1p sorting to the daughter nucleus.","method":"Co-immunoprecipitation (She2p with elongating Pol II via Spt4-Spt5), ChIP, fluorescence microscopy of mRNA localization","journal":"Genes & development","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — reciprocal Co-IP and ChIP with defined cellular phenotype, single lab","pmids":["20713510"],"is_preprint":false},{"year":2010,"finding":"Spt5 directly associates with RNA Pol I and RNA Pol II in yeast through its central region containing NusG N-terminal homology (NGN) and KOW domains. Far Western blotting identifies A190 of Pol I and Rpb1 of Pol II as direct Spt5-binding subunits. Spt5 also directly binds the Pol I initiation factor Rrn3 and ribosomal RNA.","method":"Far Western blot, direct binding assay, deletion analysis, genetic suppression assay","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct binding assay with domain deletion analysis, single lab","pmids":["21467036"],"is_preprint":false},{"year":2010,"finding":"AID interacts with Spt5, and Spt5 facilitates the association between AID and stalled RNA Pol II. shRNA screen identifies Spt5 as required for class switch recombination. ChIP-seq shows Spt5 colocalizes with AID and stalled Pol II, and Spt5 accumulation at sites of Pol II stalling predicts AID-induced mutation.","method":"shRNA screen, co-immunoprecipitation, ChIP-seq","journal":"Cell","confidence":"High","confidence_rationale":"Tier 2 / Strong — shRNA screen plus reciprocal Co-IP plus ChIP-seq, multiple orthogonal approaches, high-impact replication context","pmids":["20887897"],"is_preprint":false},{"year":2012,"finding":"The Spt5 C-terminal repeat region (CTR) is required for normal recruitment of pre-mRNA cleavage factor I (CFI) to 3' ends of S. cerevisiae genes. The CTR interacts with CFI in vitro. CFI occupancy peaks ~100 nt downstream of polyadenylation sites, likely from simultaneous binding to Spt5 CTR, nascent RNA, and Pol II phosphorylated at Ser2.","method":"ChIP, genome-wide ChIP profiling, in vitro binding assay","journal":"Molecular and cellular biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — ChIP with in vitro binding, single lab, genome-wide and directed approaches","pmids":["22290438"],"is_preprint":false},{"year":2013,"finding":"A highly conserved domain of yeast Rtf1 directly mediates a physical interaction with the Spt5 CTR. Mutations in this Rtf1 domain or deletion of the Spt5 CTR disrupt the Rtf1-Spt5 interaction and release Paf1C from chromatin. In vitro experiments confirm the direct Rtf1-Spt5 CTR interaction.","method":"Co-immunoprecipitation, in vitro direct binding assay, ChIP, mutagenesis","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — direct in vitro binding plus Co-IP plus ChIP, multiple orthogonal methods, replicated across two structural and biochemical labs","pmids":["23775116"],"is_preprint":false},{"year":2014,"finding":"Spt5 interacts with RNAP II through its KOW4-5 domains (contacting Rpb4/7 subcomplex) and through contacts with Rpb1 and Rpb2 at the clamp, protrusion, and wall domains, mapped by site-specific photocrosslinking with the unnatural amino acid p-benzoyl-L-phenylalanine. Deletion of KOW4-5 decreases transcription elongation and derepresses transcription-coupled DNA repair.","method":"Site-specific photocrosslinking with unnatural amino acid, genetic deletion analysis, TCR assay","journal":"Nucleic acids research","confidence":"High","confidence_rationale":"Tier 1 / Moderate — direct contact mapping by in vivo crosslinking at defined sites plus functional deletion analysis, single lab with two orthogonal methods","pmids":["24813444"],"is_preprint":false},{"year":2014,"finding":"Crystal structure of fission yeast RNA guanylyltransferase (GTase) bound to Spt5 CTD reveals a distinct docking site on the OB-fold domain that captures the Trp4 residue of the Spt5 nonapeptide repeat. A disruptive GTase mutation in the Spt5 CTD-binding site is synthetically lethal with mutations in the Pol2 CTD-binding site. Thr1 phosphorylation of Spt5 CTD inhibits GTase binding while Ser5-PO4 of Pol2 CTD is required.","method":"X-ray crystallography, genetic interaction (synthetic lethality), in vitro binding assays, mutagenesis","journal":"Genes & development","confidence":"High","confidence_rationale":"Tier 1 / Strong — crystal structure plus genetic validation plus mutagenesis, multiple orthogonal approaches, defines Spt5 CTD code","pmids":["24939935"],"is_preprint":false},{"year":2003,"finding":"Fission yeast Cdk9/Pch1 (ortholog of metazoan P-TEFb CDK9) phosphorylates the Spt5 CTD specifically on threonine at position 1 (Thr1) within each nonapeptide repeat. CDK9 also phosphorylates the Pol II CTD Ser residues. Autophosphorylation of both Cdk9 and its cyclin partner Pch1 was documented.","method":"In vitro kinase assay with CTD peptides and truncation mutants, phosphoamino acid analysis, mutagenesis of kinase active site","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro kinase assay with site-specific mutagenesis and phosphoamino acid analysis, single lab","pmids":["12904290"],"is_preprint":false},{"year":2010,"finding":"Deletion of the S. pombe Spt5 CTD results in slow growth and aberrant morphology, exacerbated by Pol II CTD truncation and rescued by capping enzyme overexpression, demonstrating overlapping functional roles of the Spt5 and Pol II CTDs in capping enzyme recruitment. The Spt5 CTD T1A mutation abolishes Cdk9 phosphorylation without affecting capping enzyme binding, and has a distinct positive role in elongation.","method":"Genetic analysis (deletion, alanine scanning mutagenesis, synthetic interaction), capping enzyme overexpression rescue, 6-AU sensitivity","journal":"Molecular and cellular biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — separation-of-function mutagenesis with multiple genetic assays, single lab","pmids":["20231361"],"is_preprint":false},{"year":2015,"finding":"Crystal structures of KOW1-Linker1 (K1L1) and KOW2-KOW3 domains of yeast Spt5 reveal that K1L1 displays a positively charged patch (PCP) that binds nucleic acids in vitro. The PCP is important for in vivo function and partially overlaps functionally with Spt4, suggesting KOW1 and Spt4 form functionally redundant upstream contacts during elongation.","method":"X-ray crystallography, in vitro nucleic acid binding assay, genetic growth assay","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 1 / Moderate — crystal structure plus biochemical nucleic acid binding plus genetic functional validation, single lab with three orthogonal methods","pmids":["26217010"],"is_preprint":false},{"year":2017,"finding":"Spt5 depletion in S. pombe causes RNAPII accumulation in the first ~500 bp of genes, widespread antisense transcription initiating in this barrier region, and reduced elongation rate genome-wide, demonstrating Spt5 is required for transcription past a 5'-proximal barrier and for suppression of antisense transcription.","method":"Auxin-inducible degron depletion, ChIP-seq, RNA-seq, NET-seq, MNase-seq","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 2 / Strong — genome-wide multi-method analysis with inducible depletion, four independent genome-wide approaches","pmids":["28366642"],"is_preprint":false},{"year":2017,"finding":"Spt5 KOW4-KOW5 region is essential for promoter-proximal pausing, and KOW5 directly contacts the nascent transcript (RNA cross-linking). KOW2-3 domain mediates NELF recruitment to the elongation complex. KOW1 interaction with upstream DNA helix is required for DSIF association with the Pol II elongation complex.","method":"Reconstituted in vitro pausing assay with mutant DSIF, Drosophila nuclear extract complementation, RNA cross-linking","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro reconstitution with domain mutants and direct RNA crosslinking, multiple domain-function assignments, single lab","pmids":["28213523"],"is_preprint":false},{"year":2019,"finding":"SPT5 directly interacts with MSL1 (of the Drosophila dosage compensation MSL complex) in vitro, and is required downstream of MSL complex chromatin recruitment for dosage compensation, providing mechanistic support for the elongation model of dosage compensation.","method":"Forward genetic screen, in vitro pulldown/interaction assay","journal":"PLoS genetics","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — single in vitro pulldown and genetic epistasis, single lab","pmids":["23209435"],"is_preprint":false},{"year":2022,"finding":"Spt5 contains an acidic N-terminal tail (Spt5N) with a histone-binding motif required for viability in yeast. Spt5N is sandwiched between the downstream nucleosome and upstream DNA emerging from Pol II, and prevents loss of nucleosomal histones within actively transcribed regions, coupling processive transcription to histone capture and re-deposition.","method":"Structural analysis (cryo-EM context), genetic essentiality of Spt5N motif, histone occupancy assay by ChIP","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 2 / Moderate — genetic essentiality of defined domain plus ChIP demonstration of histone loss phenotype, single lab with two orthogonal methods","pmids":["35102600"],"is_preprint":false},{"year":2022,"finding":"ZWC complex (ZC3H4, WDR82, CK2) preferentially localizes at TSS of active genes via interaction of ZC3H4/WDR82 with S5p Pol II CTD, and phosphorylates the N-terminal acidic domain of SPT5. This phosphorylation suppresses divergent antisense transcription at gene promoters.","method":"Co-IP, ChIP-seq, knockdown (ZC3H4 depletion), in vitro kinase assay, antisense RNA quantification","journal":"Nucleic acids research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP and in vitro kinase assay with ChIP-seq phenotype, single lab","pmids":["35325203"],"is_preprint":false},{"year":2022,"finding":"Spt5 depletion in mouse B cells leads to loss of super-enhancer–promoter physical interaction and Igh gene expression, correlating strictly with loss of enhancer transcription. CRISPRa rescue of enhancer transcription in Spt5-depleted cells restored Igh gene expression, while histone H3K27 acetylation, chromatin accessibility, and Mediator/cohesin at the enhancer were unaffected.","method":"Acute Spt5 depletion, 4C/Hi-C (chromatin interaction), CRISPRa rescue, nascent transcription measurement, ChIP-seq","journal":"Nature genetics","confidence":"High","confidence_rationale":"Tier 2 / Strong — acute depletion with CRISPRa rescue experiment, multiple orthogonal chromatin and transcription assays","pmids":["32251373"],"is_preprint":false},{"year":2019,"finding":"Spt5 depletion in mouse embryonic fibroblasts does not cause global elongation defects or decreased rates, but causes dislodging of a fraction of Pol II complexes during elongation specifically at 15–20 kb from the promoter, coinciding with the transition to maximum elongation speed. Long genes show greater dependency on Spt5 for optimal elongation efficiency than short genes.","method":"Spt5 depletion (auxin-inducible degron in MEFs), genome-wide elongation rate measurement, ChIP-seq","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 2 / Moderate — inducible depletion with genome-wide elongation rate measurements, single lab with well-controlled quantitative approach","pmids":["29514850"],"is_preprint":false},{"year":2019,"finding":"Spt5 modulates cotranscriptional spliceosome assembly in S. cerevisiae: Spt5 depletion impairs U5 snRNP accumulation at intron-containing genes, reducing stable cotranscriptional spliceosome assembly. Spt5 co-immunoprecipitates with core spliceosomal proteins and all spliceosomal snRNAs.","method":"Auxin-inducible degron depletion, ChIP (U5 snRNP), co-immunoprecipitation with spliceosomal snRNAs, splicing assay","journal":"RNA","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — inducible depletion with Co-IP of spliceosomal components and ChIP, single lab","pmids":["31289129"],"is_preprint":false},{"year":2025,"finding":"ARMC5 is identified as a CUL3 adaptor required for VCP/p97-dependent degradation of SPT5-depleted, promoter-proximal Pol II. ARMC5 targets promoter-proximal Pol II in a BTB domain-dependent manner, and interaction between ARMC5 and Pol II requires CDK9, supporting a phospho-dependent degradation model of defective promoter-proximal Pol II.","method":"Unbiased proteomic screening (mass spectrometry), genome-wide ChIP-seq, biochemical interaction assay, genetic domain analysis (BTB domain)","journal":"Science advances","confidence":"High","confidence_rationale":"Tier 2 / Moderate — proteomic screen plus ChIP-seq plus biochemical validation, multiple orthogonal approaches, single lab","pmids":["39854452"],"is_preprint":false},{"year":2025,"finding":"Phosphorylations of SPT5 in three regions—the KOW4-5 linker, CTR1, and CTR2—coordinately control pause release, elongation speed, and termination. CTR1 phosphorylation loss slows elongation; simultaneous CTR2 loss partially reverses this but adds effects on splicing and termination. Pausing is unaffected by CTR1 loss but increased by CTR2 loss.","method":"CRISPR phospho-mutant knock-in in human HCT116 cells, TT-seq (elongation rate), ChIP-seq, splicing and termination assays","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 2 / Strong — endogenous phospho-mutants in human cells with genome-wide elongation rate, ChIP, splicing and termination readouts, multiple orthogonal methods","pmids":["40250441"],"is_preprint":false},{"year":2023,"finding":"KOW4 domain of Spt5 promotes Pol II pausing through contact with nascent RNA, while the KOW2-3 domain mediates NELF recruitment to the elongation complex. KOW1 interaction with upstream DNA helix is required for DSIF association with Pol II. A short helical motif in the NGN domain contacts the non-template DNA strand and facilitates pausing.","method":"Purified in vitro pausing assay, Drosophila nuclear extract complementation, RNA cross-linking analysis, in vivo Drosophila viability assay","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro reconstitution with domain mutants, RNA crosslinking, and in vivo viability confirmation, multiple orthogonal methods","pmids":["37517697"],"is_preprint":false},{"year":2025,"finding":"Xrn2 (RNA exonuclease, torpedo termination factor) engages with Pol II forming a stable complex, and Spt5 stimulates Xrn2 activity to ensure efficient degradation of nascent RNA leading to Pol II dislodgement. Spt5 is also a key factor attenuating expression of non-coding transcripts, coordinates pre-mRNA splicing, and 3'-end processing.","method":"Co-immunoprecipitation (Xrn2-Pol II complex), in vitro Xrn2 activity assay, RNA-seq, splicing assay, termination assay","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro activity assay demonstrating Spt5 stimulates Xrn2 plus Co-IP and multiple genome-wide readouts, single lab with multiple orthogonal methods","pmids":["39746995"],"is_preprint":false},{"year":2023,"finding":"SEC (super elongation complex) induces SPT5 phase transition into elongation droplets during early elongation. SPT5's disordered domain is required for pause release and gene activation. Depletion of SEC increases SPT5 pausing clusters. Disease-associated SEC mutations impair phase properties of elongation droplets.","method":"Live-cell imaging of condensates, phase separation assay in vitro, SEC depletion, fluorescence microscopy","journal":"EMBO reports","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — phase separation/condensate assay with SEC depletion, single lab, emerging methodology","pmids":["36629390"],"is_preprint":false},{"year":2019,"finding":"SPT5 is required for efficient expression of HSV-1 replication-dependent γ2 late genes; siRNA knockdown of SPT5 (but not NELF-E) specifically inhibits HSV-1 late gene expression. DRB treatment reduces co-immunoprecipitation of viral ICP27 with SPT5, suggesting SPT5-ICP27 interaction is relevant for late gene expression.","method":"siRNA knockdown, RT-qPCR, co-immunoprecipitation","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — siRNA with specific phenotype and Co-IP, single lab","pmids":["28743741"],"is_preprint":false},{"year":1997,"finding":"Human SUPT5H protein is reversibly phosphorylated during mitosis, as demonstrated by purification from HeLa cells and analysis of mitotic phosphorylation state.","method":"Protein purification from HeLa cells, phosphorylation state analysis in mitotic vs. interphase cells","journal":"FEBS letters","confidence":"Medium","confidence_rationale":"Tier 3 / Weak — single biochemical analysis of mitotic phosphorylation, no functional consequence determined, single lab","pmids":["9199507"],"is_preprint":false},{"year":2016,"finding":"O-GlcNAcase (OGA) physically associates with SPT5 and TRIM28/KAP1/TIF1β, forming a purified OGA-SPT5-TIF1β complex with elongation properties in vitro. OGA activity is required for elongation in crude nuclear extract but inhibits elongation in a purified system.","method":"Co-immunoprecipitation, in vitro transcription elongation assay, ChIP-seq, protein complex purification","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — purified complex with in vitro elongation assay and ChIP-seq, single lab with multiple methods","pmids":["27601472"],"is_preprint":false},{"year":2025,"finding":"LEDGF/p75 is enriched at paused promoters and prevents phosphorylation of the SPT5 PRD/CTR1 by the super elongation complex (SEC). Deletion of the LEDGF IBD domain increases SEC occupancy and SPT5 PRD phosphorylation at promoters, leading to increased pause release. LEDGF and SEC function cooperatively on distinct SPT5 domains to control the pausing-to-elongation transition.","method":"ChIP-seq, phosphorylation assay, domain deletion analysis, CUT&RUN","journal":"Science advances","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — ChIP-seq with domain deletion analysis and phosphorylation measurements, single lab","pmids":["39823345"],"is_preprint":false},{"year":2015,"finding":"Crystal structure of fission yeast RNA triphosphatase Pct1 in complex with Spt5 CTD reveals two CTD docking sites on the Pct1 homodimer engaging TPAWN segments. Threonine phosphorylation of the Spt5 CTD antagonizes Pct1 binding, establishing a binary Spt5 CTD code where Thr1-PO4 is an 'off' switch for capping enzyme recruitment.","method":"X-ray crystallography, in vitro binding assay, phosphorylation competition assay","journal":"RNA","confidence":"High","confidence_rationale":"Tier 1 / Moderate — crystal structure plus biochemical binding assay with phosphomimetic analysis, single lab with multiple orthogonal methods","pmids":["25414009"],"is_preprint":false},{"year":2015,"finding":"Spt5 CTD Thr1 phosphorylation positively regulates histone H3K4 methylation while having minimal effect on H3K36 methylation in fission yeast. Combined Spt5 and Rpb1 CTD mutations have additive effects on H3K36me, suggesting overlapping roles. Pol II Ser2 phosphorylation by Lsk1/Cdk12 positively regulates H3K36me but negatively regulates H3K4me.","method":"Phospho-site mutagenesis (alanine substitutions), histone modification western blot and ChIP, genetic epistasis","journal":"Nucleic acids research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — systematic CTD phospho-site mutagenesis with histone modification readouts, single lab","pmids":["26275777"],"is_preprint":false},{"year":2022,"finding":"Spt5 depletion extends Pol II pausing zones beyond the canonical 40–100 bp window to 0.3–3 kb into genes. Phosphomimetic substitutions in CTR1 diminish pausing throughout genes, while mutations preventing phosphorylation of the Spt5 RNA-binding linker (KOW4-5 domain) strengthen pausing, revealing distinct phospho-isoforms that set the balance between pausing and elongation.","method":"Spt5 depletion with phospho-mutant rescue, eNET-seq (elongating polymerase mapping), PTEFb inhibition","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 2 / Strong — genome-wide eNET-seq with phospho-mutant rescue and kinase inhibition, multiple orthogonal approaches defining phospho-isoform functions","pmids":["36206739"],"is_preprint":false}],"current_model":"SUPT5H/SPT5 is an essential, universally conserved transcription elongation factor that forms the DSIF complex with SPT4; it directly associates with RNA Pol II via its NGN and KOW domains to regulate processive elongation, stabilizes promoter-proximal Pol II against ubiquitin-mediated degradation (via Cullin 3-ARMC5), promotes pause release and elongation through CDK9-dependent phosphorylation of its linker and CTR1/CTR2 repeat domains (which are dephosphorylated by PNUTS-PP1 to trigger Pol II deceleration and Xrn2-mediated termination), recruits the PAF complex through its phospho-CTR interacting with Rtf1/Plus3, recruits mRNA capping enzymes to nascent transcripts, suppresses divergent antisense transcription, facilitates cotranscriptional splicing, and is regulated post-translationally by PRMT1/PRMT5 arginine methylation and by CK2-mediated phosphorylation of its N-terminal acidic domain."},"narrative":{"mechanistic_narrative":"SUPT5H/SPT5 is an essential, deeply conserved transcription elongation factor that, together with SPT4, forms the DSIF complex and governs the processivity of RNA polymerase II across the transcription cycle [PMID:9450929, PMID:1840633]. SPT5 binds Pol II directly through its central NusG N-terminal homology (NGN) and KOW domains—with KOW4-5 contacting the Rpb4/7 subcomplex and Rpb1/Rpb2 clamp, KOW5 contacting nascent RNA, and KOW1 engaging upstream DNA to anchor DSIF on the elongation complex [PMID:24813444, PMID:28213523]—while SPT4 binds the NGN domain through an acid-dipole interface that maintains KOW conformation [PMID:19000817]. DSIF exerts dual control over Pol II: it enforces promoter-proximal pausing (in part through KOW2-3-mediated NELF recruitment) and is also required for processive elongation, with depletion causing loss of paused Pol II and processivity defects that are most pronounced in long genes [PMID:9450929, PMID:28213523, PMID:34534457, PMID:29514850]. This balance is set by phosphorylation: P-TEFb/CDK9 phosphorylates the C-terminal repeat (CTR) and the KOW4-5 linker to drive pause release, and coordinated phospho-states of the linker, CTR1, and CTR2 tune elongation speed, pausing, splicing, and termination [PMID:10757782, PMID:12904290, PMID:34534457, PMID:40250441, PMID:36206739]. The phosphorylated Spt5 CTR provides a docking platform that recruits the PAF complex via Rtf1's Plus3 domain and licenses downstream histone modifications including H2B monoubiquitination and H3K4/K36 methylation [PMID:19581288, PMID:19365074, PMID:24101474, PMID:23775116]; the CTR nonapeptide repeats also recruit mRNA capping enzymes through a Thr1-phosphorylation-controlled binary code [PMID:11893740, PMID:24939935, PMID:25414009]. At gene 3' ends, PNUTS-PP1 dephosphorylates Spt5 to decelerate Pol II and license Xrn2-mediated torpedo termination, with Spt5 directly stimulating Xrn2 nuclease activity [PMID:31677974, PMID:39746995]. SPT5 stabilizes promoter-proximal Pol II against Cullin 3/ARMC5- and VCP/p97-mediated ubiquitin-proteasomal degradation of RPB1 in a CDK9-dependent manner [PMID:34480849, PMID:39854452], suppresses divergent and antisense transcription [PMID:28366642, PMID:35325203], facilitates cotranscriptional spliceosome assembly [PMID:31289129], couples transcription to histone retention via an acidic N-terminal tail [PMID:35102600], and is required for enhancer transcription and super-enhancer-promoter contacts [PMID:32251373]. SPT5 is additionally co-opted in specialized contexts including MYC-driven elongation [PMID:30928206], AID-dependent class switch recombination [PMID:20887897], and herpesvirus late gene expression [PMID:28743741], and is regulated post-translationally by PRMT1/PRMT5 arginine methylation [PMID:12718890] and CK2-family phosphorylation of its N-terminal acidic domain [PMID:35325203].","teleology":[{"year":1991,"claim":"Established that SPT5 is an essential nuclear protein, framing it as a broadly required transcription factor rather than a gene-specific regulator.","evidence":"Null mutant lethality and immunofluorescence of an SPT5-β-galactosidase fusion in yeast","pmids":["1840633"],"confidence":"High","gaps":["Did not define molecular function or interaction partners","No mechanism linking essentiality to transcription"]},{"year":1998,"claim":"Identified SPT5/SPT4 as the DSIF complex and resolved its paradoxical dual role in restraining and stimulating Pol II elongation, defining SPT5 as a core elongation factor.","evidence":"Biochemical purification from HeLa extracts with in vitro transcription assays, plus yeast co-IP and allele-specific genetic suppression by Pol II mutants","pmids":["9450929","9450930"],"confidence":"High","gaps":["Domain basis of Pol II contact not yet mapped","Mechanistic switch between positive and negative roles unresolved"]},{"year":2000,"claim":"Mapped the modular domain architecture of SPT5 and identified CTR1 as a P-TEFb substrate, providing the first link between SPT5 phosphorylation and elongation control.","evidence":"Domain deletion in vitro transcription and recombinant P-TEFb phosphorylation assays; polytene/ChIP localization to elongating Pol II in Drosophila","pmids":["10757782","11040217","11040216"],"confidence":"High","gaps":["Phosphorylation sites within CTR not defined","Downstream effectors of phospho-CTR unknown"]},{"year":2002,"claim":"Defined SPT5 as a stage-specific elongation factor required in late elongation to prevent premature RNA dissociation, refining when in the cycle SPT5 acts.","evidence":"In vitro three-stage HIV-1 transcription with immunodepletion and chase experiments","pmids":["11809800"],"confidence":"High","gaps":["In vitro system may not capture chromatin context","Did not connect to physiological terminator architecture"]},{"year":2003,"claim":"Connected the Spt5 CTD to mRNA capping and identified arginine methylation as a regulatory input, establishing SPT5 as a hub coupling elongation to co-transcriptional RNA processing.","evidence":"Two-hybrid/in vitro binding of CTD to capping enzymes; PRMT1/PRMT5 in vitro methylation with arginine mutagenesis; CDK9 phosphorylation of CTD Thr1","pmids":["11893740","12718890","12904290","12556496"],"confidence":"High","gaps":["Functional consequence of methylation in vivo not quantified","Capping-recruitment regulation by phosphorylation not yet structurally resolved"]},{"year":2009,"claim":"Demonstrated that kinase-dependent phosphorylation of the Spt5 CTR recruits the PAF complex and licenses elongation-coupled histone modifications, defining a phospho-CTR-to-chromatin signaling axis.","evidence":"Analog-sensitive Bur1 kinase chemical genetics, in vitro kinase assays on isolated elongation complexes, ChIP, and histone modification analysis","pmids":["19581288","19365074"],"confidence":"High","gaps":["Direct CTR-PAF binding interface not resolved at this stage","Ordering of H2B ubiquitination relative to H3 methylation unclear"]},{"year":2008,"claim":"Provided the structural basis for SPT4-SPT5 assembly, explaining how SPT4 maintains the elongation-competent conformation of SPT5 KOW domains.","evidence":"Crystal structure of Spt4-NGN with interface mutagenesis and archaeal complex reconstitution","pmids":["19000817"],"confidence":"High","gaps":["Did not capture SPT5 in the context of Pol II","KOW domain functions inferred, not directly tested"]},{"year":2013,"claim":"Defined at atomic resolution how phosphorylated Spt5 CTR is read by Rtf1/Plus3, establishing the molecular recruitment mechanism for the PAF complex.","evidence":"X-ray structure of Rtf1 Plus3 with phospho-Spt5 repeat, in vitro binding mutagenesis, and ChIP; complemented by direct Rtf1-CTR interaction mapping","pmids":["24101474","23775116"],"confidence":"High","gaps":["Stoichiometry of multivalent CTR-PAF engagement unresolved","Kinase specificity setting the phospho-mark in human cells not addressed"]},{"year":2014,"claim":"Mapped SPT5-Pol II contacts at residue resolution and decoded the capping-enzyme CTD recognition code, showing how phosphorylation toggles processing factor recruitment.","evidence":"Site-specific photocrosslinking with unnatural amino acids mapping KOW4-5/Rpb contacts; crystal structures of guanylyltransferase-CTD with synthetic-lethality validation","pmids":["24813444","24939935"],"confidence":"High","gaps":["Dynamics of contact remodeling during the cycle not captured","Coupling of CTD code to elongation rate not directly measured"]},{"year":2010,"claim":"Broadened the SPT5 functional repertoire to Pol I association, mRNA localization, and AID-dependent class switch recombination, indicating SPT5 acts as a general elongation scaffold co-opted for specialized outcomes.","evidence":"Far Western direct binding to Pol I/II subunits; co-IP linking She2p to elongating Pol II; shRNA screen plus co-IP/ChIP-seq for AID at stalled Pol II","pmids":["21467036","20713510","20887897"],"confidence":"Medium","gaps":["Pol I role mechanistically distinct from elongation not detailed","She2p link single-lab without structural detail"]},{"year":2015,"claim":"Resolved KOW domain structures and the CTD capping code in detail, showing nucleic-acid-binding surfaces and Thr1 phosphorylation as a binary off-switch for capping enzyme recruitment.","evidence":"Crystal structures of KOW1-Linker1/KOW2-3 and of Pct1-CTD with binding/competition assays; phospho-site mutagenesis linking CTD Thr1 to H3K4 methylation","pmids":["26217010","25414009","26275777"],"confidence":"High","gaps":["Redundancy between KOW1 PCP and Spt4 not fully quantified in vivo","Whether the human CTR uses an identical code not established here"]},{"year":2017,"claim":"Genome-wide depletion studies established SPT5 as required to overcome a 5'-proximal elongation barrier and to suppress pervasive antisense transcription, defining its role in transcription directionality and progression.","evidence":"Auxin-inducible degron depletion in S. pombe with ChIP-seq, RNA-seq, NET-seq, MNase-seq; in vitro reconstituted pausing with KOW domain mutants assigning NELF recruitment and nascent-RNA contacts","pmids":["28366642","28213523"],"confidence":"High","gaps":["Barrier composition not molecularly defined","How SPT5 distinguishes sense from antisense initiation unclear"]},{"year":2019,"claim":"Defined SPT5 dephosphorylation as the trigger for Pol II deceleration and torpedo termination, and quantified SPT5's contribution to elongation processivity in long genes.","evidence":"Genome-wide elongation-rate measurement with PNUTS-PP1 separation-of-function mutation; auxin-degron depletion in MEFs with elongation rate mapping; MYC-SPT5 transfer mechanism by MS/Co-IP/ChIP-seq","pmids":["31677974","29514850","30928206"],"confidence":"High","gaps":["Phosphatase site specificity on Spt5 not fully resolved","MYC sequestration model not extended to other oncogenic contexts"]},{"year":2021,"claim":"Showed SPT5 actively protects promoter-proximal Pol II from ubiquitin-proteasomal destruction and is required for pause establishment and release, distinguishing its role from NELF.","evidence":"Auxin- and dTAG-inducible depletion with ubiquitination assays, Cullin 3/VCP/CDK9 dependency, PRO-seq/ChIP-seq/ATAC-seq, and phospho-mutant analysis of Ser666","pmids":["34480849","34534457"],"confidence":"High","gaps":["E3 adaptor identity not yet defined at this stage","Coupling between Pol II protection and pause release mechanism incomplete"]},{"year":2022,"claim":"Refined the phospho-isoform logic of pausing versus elongation and revealed SPT5's acidic N-tail in histone retention and antisense suppression, expanding its chromatin-coupling roles.","evidence":"eNET-seq with CTR1/linker phospho-mutant rescue; cryo-EM-context analysis with histone occupancy ChIP for Spt5N; ZWC (ZC3H4/WDR82/CK2) in vitro kinase and ChIP-seq; super-enhancer 4C/Hi-C with CRISPRa rescue","pmids":["36206739","35102600","35325203","32251373"],"confidence":"High","gaps":["Relative contribution of distinct phospho-isoforms across gene classes not unified","ZWC-SPT5 axis confirmed in single lab"]},{"year":2025,"claim":"Identified ARMC5 as the CUL3 adaptor for promoter-proximal Pol II degradation, dissected coordinated CTR1/CTR2/linker phospho-control, and showed SPT5 directly stimulates Xrn2 to drive termination, integrating the elongation-to-termination program.","evidence":"Proteomic screen with BTB-domain/CDK9-dependent ARMC5 validation; CRISPR phospho-mutant knock-ins in HCT116 with TT-seq/ChIP-seq; in vitro Xrn2 activity assays with Co-IP and genome-wide readouts","pmids":["39854452","40250441","39746995"],"confidence":"High","gaps":["How phospho-marks are spatially ordered across the gene not fully resolved","Direct structure of SPT5-Xrn2 stimulation absent"]},{"year":null,"claim":"How the full set of SPT5 phosphorylation marks, arginine methylation, and condensate/phase behavior are integrated kinetically to switch SPT5 between pausing, elongation, processing, and termination across distinct gene architectures remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No unified quantitative model linking each PTM to a defined cycle step","Condensate-based regulation (SEC/LEDGF) characterized only in single labs","Crosstalk between methylation and phosphorylation in vivo undefined"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0003723","term_label":"RNA binding","supporting_discovery_ids":[28,37,26]},{"term_id":"GO:0003677","term_label":"DNA binding","supporting_discovery_ids":[26,37]},{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[11,21,8]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[0,13,38]},{"term_id":"GO:0140110","term_label":"transcription regulator activity","supporting_discovery_ids":[0,3,16]}],"localization":[{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[2]},{"term_id":"GO:0000228","term_label":"nuclear chromosome","supporting_discovery_ids":[4]},{"term_id":"GO:0005654","term_label":"nucleoplasm","supporting_discovery_ids":[4,1]}],"pathway":[{"term_id":"R-HSA-74160","term_label":"Gene expression (Transcription)","supporting_discovery_ids":[0,1,16,27]},{"term_id":"R-HSA-4839726","term_label":"Chromatin organization","supporting_discovery_ids":[9,10,30,45]},{"term_id":"R-HSA-8953854","term_label":"Metabolism of RNA","supporting_discovery_ids":[8,34,38,20]},{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[15,35]}],"complexes":["DSIF (SPT4-SPT5)"],"partners":["SUPT4H1","POLR2A","RTF1","XRN2","MYC","AICDA","ARMC5","MSL1"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"O00267","full_name":"Transcription elongation factor SPT5","aliases":["DRB sensitivity-inducing factor 160 kDa subunit","DSIF p160","DRB sensitivity-inducing factor large subunit","DSIF large subunit","Tat-cotransactivator 1 protein","Tat-CT1 protein"],"length_aa":1087,"mass_kda":121.0,"function":"Component of the DRB sensitivity-inducing factor complex (DSIF complex), which regulates mRNA processing and transcription elongation by RNA polymerase II (PubMed:10075709, PubMed:10199401, PubMed:10421630, PubMed:10757782, PubMed:10912001, PubMed:11112772, PubMed:11553615, PubMed:12653964, PubMed:12718890, PubMed:15136722, PubMed:15380072, PubMed:9450929, PubMed:9857195). DSIF positively regulates mRNA capping by stimulating the mRNA guanylyltransferase activity of RNGTT/CAP1A (PubMed:10075709, PubMed:10421630, PubMed:10757782, PubMed:10912001, PubMed:11112772, PubMed:11553615, PubMed:12653964, PubMed:12718890, PubMed:15136722, PubMed:15380072, PubMed:9450929, PubMed:9857195). DSIF also acts cooperatively with the negative elongation factor complex (NELF complex) to enhance transcriptional pausing at sites proximal to the promoter (PubMed:10075709, PubMed:10199401, PubMed:10757782, PubMed:10912001, PubMed:11112772, PubMed:11553615, PubMed:12653964, PubMed:12718890, PubMed:15136722, PubMed:15380072, PubMed:9450929, PubMed:9857195). Transcriptional pausing may facilitate the assembly of an elongation competent RNA polymerase II complex (PubMed:10075709, PubMed:10199401, PubMed:10421630, PubMed:10757782, PubMed:10912001, PubMed:11112772, PubMed:11553615, PubMed:12653964, PubMed:12718890, PubMed:15136722, PubMed:15380072, PubMed:9450929, PubMed:9857195). DSIF and NELF promote pausing by inhibition of the transcription elongation factor TFIIS/S-II (PubMed:16214896). TFIIS/S-II binds to RNA polymerase II at transcription pause sites and stimulates the weak intrinsic nuclease activity of the enzyme (PubMed:16214896). Cleavage of blocked transcripts by RNA polymerase II promotes the resumption of transcription from the new 3' terminus and may allow repeated attempts at transcription through natural pause sites (PubMed:16214896). Following phosphorylation by CDK9, DSIF can also positively regulate transcriptional elongation (PubMed:16427012). Required for the efficient activation of transcriptional elongation by the HIV-1 nuclear transcriptional activator, Tat (PubMed:10393184, PubMed:10454543, PubMed:11809800, PubMed:9514752). DSIF acts to suppress transcriptional pausing in transcripts derived from the HIV-1 LTR and blocks premature release of HIV-1 transcripts at terminator sequences (PubMed:11112772, PubMed:14701750)","subcellular_location":"Nucleus","url":"https://www.uniprot.org/uniprotkb/O00267/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":true,"resolved_as":"","url":"https://depmap.org/portal/gene/SUPT5H","classification":"Common Essential","n_dependent_lines":1201,"n_total_lines":1208,"dependency_fraction":0.9942052980132451},"opencell":{"profiled":true,"resolved_as":"","ensg_id":"ENSG00000196235","cell_line_id":"CID001075","localizations":[{"compartment":"nucleoplasm","grade":3},{"compartment":"nuclear_punctae","grade":1}],"interactors":[{"gene":"SUPT4H1","stoichiometry":10.0},{"gene":"POLR2B","stoichiometry":4.0},{"gene":"POLR2E","stoichiometry":4.0},{"gene":"POLR2F","stoichiometry":4.0},{"gene":"POLR2I","stoichiometry":4.0},{"gene":"POLR2J","stoichiometry":4.0},{"gene":"POLR2K","stoichiometry":4.0},{"gene":"SSRP1","stoichiometry":4.0},{"gene":"SMEK1","stoichiometry":4.0},{"gene":"POLR2L","stoichiometry":4.0}],"url":"https://opencell.sf.czbiohub.org/target/CID001075","total_profiled":1310},"omim":[{"mim_id":"619818","title":"ELONGATION FACTOR 1; ELOF1","url":"https://www.omim.org/entry/619818"},{"mim_id":"611180","title":"NEGATIVE ELONGATION FACTOR COMPLEX, MEMBER B; NELFB","url":"https://www.omim.org/entry/611180"},{"mim_id":"606026","title":"NEGATIVE ELONGATION FACTOR COMPLEX, MEMBER A; NELFA","url":"https://www.omim.org/entry/606026"},{"mim_id":"605297","title":"NEGATIVE ELONGATION FACTOR COMPLEX, MEMBER C/D; NELFCD","url":"https://www.omim.org/entry/605297"},{"mim_id":"603555","title":"SPT4 HOMOLOG, DSIF ELONGATION FACTOR SUBUNIT; SUPT4H1","url":"https://www.omim.org/entry/603555"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Nucleoplasm","reliability":"Supported"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/SUPT5H"},"hgnc":{"alias_symbol":["SPT5H","SPT5","FLJ34157"],"prev_symbol":[]},"alphafold":{"accession":"O00267","domains":[{"cath_id":"3.30.70.940","chopping":"171-265","consensus_level":"high","plddt":94.0818,"start":171,"end":265},{"cath_id":"-","chopping":"278-395","consensus_level":"medium","plddt":85.8917,"start":278,"end":395},{"cath_id":"-","chopping":"539-646","consensus_level":"medium","plddt":89.2483,"start":539,"end":646},{"cath_id":"2.30.30.30","chopping":"709-752","consensus_level":"high","plddt":93.2716,"start":709,"end":752},{"cath_id":"2.30.30.30","chopping":"985-1084","consensus_level":"medium","plddt":92.1532,"start":985,"end":1084}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/O00267","model_url":"https://alphafold.ebi.ac.uk/files/AF-O00267-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-O00267-F1-predicted_aligned_error_v6.png","plddt_mean":68.56},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=SUPT5H","jax_strain_url":"https://www.jax.org/strain/search?query=SUPT5H"},"sequence":{"accession":"O00267","fasta_url":"https://rest.uniprot.org/uniprotkb/O00267.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/O00267/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/O00267"}},"corpus_meta":[{"pmid":"9450929","id":"PMC_9450929","title":"DSIF, a novel transcription elongation factor that regulates RNA polymerase II processivity, is composed of human Spt4 and Spt5 homologs.","date":"1998","source":"Genes & development","url":"https://pubmed.ncbi.nlm.nih.gov/9450929","citation_count":626,"is_preprint":false},{"pmid":"9450930","id":"PMC_9450930","title":"Evidence that Spt4, Spt5, and Spt6 control transcription elongation by RNA polymerase II in Saccharomyces cerevisiae.","date":"1998","source":"Genes & development","url":"https://pubmed.ncbi.nlm.nih.gov/9450930","citation_count":393,"is_preprint":false},{"pmid":"20887897","id":"PMC_20887897","title":"Activation-induced cytidine deaminase targets DNA at sites of RNA polymerase II stalling by interaction with Spt5.","date":"2010","source":"Cell","url":"https://pubmed.ncbi.nlm.nih.gov/20887897","citation_count":300,"is_preprint":false},{"pmid":"12556496","id":"PMC_12556496","title":"Dual roles for Spt5 in pre-mRNA processing and transcription elongation revealed by identification of Spt5-associated proteins.","date":"2003","source":"Molecular and cellular biology","url":"https://pubmed.ncbi.nlm.nih.gov/12556496","citation_count":243,"is_preprint":false},{"pmid":"11040217","id":"PMC_11040217","title":"High-resolution localization of Drosophila Spt5 and Spt6 at heat shock genes in vivo: roles in promoter proximal pausing and transcription elongation.","date":"2000","source":"Genes & development","url":"https://pubmed.ncbi.nlm.nih.gov/11040217","citation_count":236,"is_preprint":false},{"pmid":"12718890","id":"PMC_12718890","title":"Methylation of SPT5 regulates its interaction with RNA polymerase II and transcriptional elongation properties.","date":"2003","source":"Molecular cell","url":"https://pubmed.ncbi.nlm.nih.gov/12718890","citation_count":199,"is_preprint":false},{"pmid":"11040216","id":"PMC_11040216","title":"Spt5 and spt6 are associated with active transcription and have characteristics of general elongation factors in D. 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In vitro, DSIF also stimulates elongation rate at limiting NTP concentrations, demonstrating dual positive and negative roles in Pol II processivity.\",\n      \"method\": \"Biochemical purification from HeLa extracts, in vitro transcription assay, cDNA cloning, recombinant protein complementation\",\n      \"journal\": \"Genes & development\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro reconstitution with purified factor, multiple assays, replicated in parallel yeast study (PMID:9450930)\",\n      \"pmids\": [\"9450929\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1998,\n      \"finding\": \"Yeast Spt5 physically associates with RNA polymerase II in vivo (co-immunoprecipitation), and genetic suppression of conditional spt5 mutations by mutations in the two largest Pol II subunits (one of which causes an elongation defect) places Spt5 in the transcription elongation machinery. Spt4 and Spt5 form a tight complex that does not contain Spt6.\",\n      \"method\": \"Co-immunoprecipitation, genetic epistasis (allele-specific suppression by Pol II mutants), conditional mutant phenotyping\",\n      \"journal\": \"Genes & development\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal genetic and biochemical evidence, replicated across two simultaneous publications\",\n      \"pmids\": [\"9450930\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1991,\n      \"finding\": \"Yeast SPT5 is an essential nuclear protein; null mutation is lethal, indicating requirement for normal transcription of many genes. The protein localizes to the nucleus by indirect immunofluorescence of an SPT5-β-galactosidase fusion.\",\n      \"method\": \"Null mutant construction, indirect immunofluorescence of fusion protein, SPT5 cloning and sequencing\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — direct genetic essentiality plus subcellular localization experiment, replicated in subsequent studies\",\n      \"pmids\": [\"1840633\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"SPT5 domains required for transcriptional regulation were defined: the SPT4-binding domain, the RNA Pol II-binding domain, and the C-terminal repeat region CTR1 are all required for DRB-mediated transcriptional repression and Tat-mediated activation in vitro. The CTR1 domain is a substrate for P-TEFb (CDK9/cyclin T1) phosphorylation.\",\n      \"method\": \"Domain deletion/truncation analysis, in vitro transcription assay, phosphorylation assay with recombinant P-TEFb\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro transcription assay with mutagenesis and direct phosphorylation assay, single lab with multiple orthogonal methods\",\n      \"pmids\": [\"10757782\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"Drosophila Spt5 colocalizes with actively elongating (phosphorylated) RNA Pol II but not with non-elongating Pol II at polytene chromosome loci, and is recruited to heat shock gene promoters before heat shock and to 5' and 3' ends of genes after heat shock induction, consistent with roles in promoter-proximal pausing and elongation.\",\n      \"method\": \"Immunofluorescence on polytene chromosomes, chromatin immunoprecipitation (ChIP)\",\n      \"journal\": \"Genes & development\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — direct localization with functional consequence, two independent Drosophila studies published simultaneously\",\n      \"pmids\": [\"11040217\", \"11040216\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"SPT5 is specifically methylated by protein arginine methyltransferases PRMT1 and PRMT5. Specific arginine residues in SPT5 are methylated by these enzymes, and methylation regulates SPT5 interaction with RNA polymerase II, its promoter association, and its transcriptional elongation properties.\",\n      \"method\": \"Biochemical co-association assay, in vitro methylation assay, mutagenesis of arginine residues, co-immunoprecipitation with Pol II\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro methylation assay plus mutagenesis and interaction mapping, single lab with multiple orthogonal methods\",\n      \"pmids\": [\"12718890\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Yeast Spt5 co-immunopurifies with general elongation factors TFIIF and TFIIS, chromatin regulators Spt6 and FACT, and mRNA capping enzyme and cap methyltransferase. spt4 and spt5 mutations genetically interact with capping enzyme gene mutations and lead to accumulation of unspliced pre-mRNA, revealing roles in pre-mRNA processing.\",\n      \"method\": \"Co-immunopurification/mass spectrometry, genetic interaction analysis, pre-mRNA accumulation assay\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal co-IP with MS plus genetic interactions, single lab with multiple orthogonal methods\",\n      \"pmids\": [\"12556496\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"Spt5 is recruited to the HIV-1 transcription complex shortly after initiation. CDK9 activation induces hyperphosphorylation of Spt5 in parallel with Pol II CTD phosphorylation. Spt5-depleted extracts show Spt5 is not required for early elongation or Tat-dependent kinase activation, but is required in late elongation to prevent premature dissociation of RNA from the transcription complex at terminator sequences and to reduce polymerase pausing at arrest sites.\",\n      \"method\": \"In vitro three-stage transcription assay, immunodepletion, chase experiments with Spt5-depleted extracts\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro reconstitution with immunodepletion, multiple assays defining stage-specific function, single lab\",\n      \"pmids\": [\"11809800\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"Fission yeast Spt5 C-terminal domain (CTD), composed of nonapeptide repeats (TPAWNSGSK), is necessary and sufficient for binding to mRNA capping enzymes Pct1 (triphosphatase) and Pce1 (guanylyltransferase), both in two-hybrid and in vitro binding assays. Spt5 is essential in S. pombe and interacts with Spt4 via a central domain distinct from the CTD.\",\n      \"method\": \"Two-hybrid assay, in vitro binding assay with CTD truncations, genetic complementation\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro binding assay plus two-hybrid, domain mapping with multiple truncations, single lab\",\n      \"pmids\": [\"11893740\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"The yeast Bur1 kinase directly phosphorylates the Spt5 C-terminal repeat domain (CTD) both in vivo and in isolated elongation complexes in vitro. Deletion of the Spt5 CTD or mutation of Spt5 serines targeted by Bur1 reduces PAF complex recruitment, decreases histone H3K4 trimethylation, and reduces Pol II CTD Ser-2 phosphorylation.\",\n      \"method\": \"Chemical genetics (analog-sensitive kinase), in vitro kinase assay with isolated elongation complexes, ChIP, histone modification analysis\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — chemical genetics plus in vitro kinase assay and ChIP, multiple orthogonal readouts, single lab\",\n      \"pmids\": [\"19581288\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"BUR kinase phosphorylates the Spt5 CTR in vivo and in vitro, and the Spt5 CTR is required for PAF complex recruitment, histone H2B K123 monoubiquitination, and histone H3 K4/K36 trimethylation during transcription elongation.\",\n      \"method\": \"In vitro kinase assay, ChIP, histone modification western blot, genetic deletion analysis\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro kinase assay plus ChIP and genetic analysis, multiple chromatin modification readouts, single lab\",\n      \"pmids\": [\"19365074\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Crystal structure of human Rtf1 Plus3 domain in complex with a phosphorylated Spt5 repeat reveals that Spt5 binding is mediated by a phosphothreonine recognition interface and hydrophobic contacts. Mutations disrupting this interface diminish Spt5 binding in vitro and Rtf1 chromatin localization in vivo, establishing the molecular basis for Paf1C recruitment by phosphorylated Spt5.\",\n      \"method\": \"X-ray crystallography, in vitro binding assay, ChIP (chromatin localization)\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — crystal structure plus in vitro binding mutagenesis plus in vivo chromatin localization, multiple orthogonal methods\",\n      \"pmids\": [\"24101474\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Crystal structure of yeast Spt4 bound to the NGN domain of Spt5 reveals an acid-dipole interaction governing Spt4-Spt5 binding. Mutations disrupting this interaction disrupt the complex. The archaeal Spt4-Spt5 homologs also form a complex, and Spt4 is positioned to maintain the functional conformation of KOW domains in Spt5.\",\n      \"method\": \"X-ray crystallography, mutagenesis of interface residues, archaeal complex reconstitution\",\n      \"journal\": \"Structure\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — crystal structure plus mutagenesis validation, replicated in archaeal system, single study with multiple orthogonal methods\",\n      \"pmids\": [\"19000817\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"PNUTS-PP1 phosphatase dephosphorylates Spt5 downstream of poly(A) sites, causing RNA Pol II deceleration from >2 kb/min to <1 kb/min. This deceleration is required for transcription termination by allowing Xrn2 to catch and torpedo Pol II ('sitting duck torpedo' mechanism). Disruption of PP1 binding (PNUTS W401A) causes genome-wide transcription acceleration and Spt5 hyper-phosphorylation.\",\n      \"method\": \"Genome-wide elongation rate measurement (TT-seq/metabolic labeling), ChIP-seq, mutant cell lines, PP1-binding mutation\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genome-wide functional assay with separation-of-function mutation and defined mechanistic readout, multiple orthogonal approaches\",\n      \"pmids\": [\"31677974\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"MYC directly binds SPT5 and recruits SPT5 to promoters, enabling CDK7-dependent transfer of SPT5 onto Pol II to promote fast and processive transcription elongation. At oncogenic MYC levels, SPT5 is sequestered into non-functional complexes decreasing expression of growth-suppressive genes.\",\n      \"method\": \"Mass spectrometry of MYC and Pol II complexes, co-immunoprecipitation, ChIP-seq, elongation rate measurements\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal Co-IP, MS, ChIP-seq and functional elongation assays, single lab with multiple orthogonal methods\",\n      \"pmids\": [\"30928206\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Acute depletion of SPT5 triggers ubiquitination and proteasomal degradation of the core Pol II subunit RPB1 specifically at promoter-proximal regions, mediated by E3 ligase Cullin 3, unfoldase VCP/p97, and a CDK9 kinase complex. This demonstrates that SPT5 stabilizes Pol II at promoter-proximal regions and is required for Pol II release into gene bodies.\",\n      \"method\": \"Auxin-inducible degron depletion, ubiquitination assay, proteasome inhibitor rescue, genetic complementation in yeast (evolutionary conservation), ChIP\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — acute inducible depletion with multiple mechanistic rescue experiments, evolutionary conservation shown, multiple orthogonal methods\",\n      \"pmids\": [\"34480849\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Rapid SPT5 depletion causes pronounced reduction of paused Pol II at both promoters and enhancers, distinct from NELF depletion; impairs transcription activation; alters enhancer chromatin landscape; and causes Pol II processivity defects in gene bodies. Phosphorylation of SPT5 linker Ser666 by P-TEFb promotes pause release; this is antagonized by Integrator-PP2A (INTAC) targeting SPT5 and Pol II. SPT5 C-terminal region phosphorylation links to 3' end termination.\",\n      \"method\": \"Rapid degradation (dTAG system), ChIP-seq, PRO-seq, ATAC-seq, phospho-mutant analysis\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — rapid depletion system with genome-wide and phospho-mutant analysis across multiple chromatin and transcriptional readouts, multiple orthogonal methods\",\n      \"pmids\": [\"34534457\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Spt5 interacts in vivo with the elongating form of RNA Pol II, and mutations in SPT4 or SPT5 reduce cotranscriptional recruitment of the RNA-binding protein She2p to the ASH1 gene, disrupting ASH1 mRNA localization to the bud tip and Ash1p sorting to the daughter nucleus.\",\n      \"method\": \"Co-immunoprecipitation (She2p with elongating Pol II via Spt4-Spt5), ChIP, fluorescence microscopy of mRNA localization\",\n      \"journal\": \"Genes & development\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal Co-IP and ChIP with defined cellular phenotype, single lab\",\n      \"pmids\": [\"20713510\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Spt5 directly associates with RNA Pol I and RNA Pol II in yeast through its central region containing NusG N-terminal homology (NGN) and KOW domains. Far Western blotting identifies A190 of Pol I and Rpb1 of Pol II as direct Spt5-binding subunits. Spt5 also directly binds the Pol I initiation factor Rrn3 and ribosomal RNA.\",\n      \"method\": \"Far Western blot, direct binding assay, deletion analysis, genetic suppression assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct binding assay with domain deletion analysis, single lab\",\n      \"pmids\": [\"21467036\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"AID interacts with Spt5, and Spt5 facilitates the association between AID and stalled RNA Pol II. shRNA screen identifies Spt5 as required for class switch recombination. ChIP-seq shows Spt5 colocalizes with AID and stalled Pol II, and Spt5 accumulation at sites of Pol II stalling predicts AID-induced mutation.\",\n      \"method\": \"shRNA screen, co-immunoprecipitation, ChIP-seq\",\n      \"journal\": \"Cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — shRNA screen plus reciprocal Co-IP plus ChIP-seq, multiple orthogonal approaches, high-impact replication context\",\n      \"pmids\": [\"20887897\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"The Spt5 C-terminal repeat region (CTR) is required for normal recruitment of pre-mRNA cleavage factor I (CFI) to 3' ends of S. cerevisiae genes. The CTR interacts with CFI in vitro. CFI occupancy peaks ~100 nt downstream of polyadenylation sites, likely from simultaneous binding to Spt5 CTR, nascent RNA, and Pol II phosphorylated at Ser2.\",\n      \"method\": \"ChIP, genome-wide ChIP profiling, in vitro binding assay\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — ChIP with in vitro binding, single lab, genome-wide and directed approaches\",\n      \"pmids\": [\"22290438\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"A highly conserved domain of yeast Rtf1 directly mediates a physical interaction with the Spt5 CTR. Mutations in this Rtf1 domain or deletion of the Spt5 CTR disrupt the Rtf1-Spt5 interaction and release Paf1C from chromatin. In vitro experiments confirm the direct Rtf1-Spt5 CTR interaction.\",\n      \"method\": \"Co-immunoprecipitation, in vitro direct binding assay, ChIP, mutagenesis\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — direct in vitro binding plus Co-IP plus ChIP, multiple orthogonal methods, replicated across two structural and biochemical labs\",\n      \"pmids\": [\"23775116\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Spt5 interacts with RNAP II through its KOW4-5 domains (contacting Rpb4/7 subcomplex) and through contacts with Rpb1 and Rpb2 at the clamp, protrusion, and wall domains, mapped by site-specific photocrosslinking with the unnatural amino acid p-benzoyl-L-phenylalanine. Deletion of KOW4-5 decreases transcription elongation and derepresses transcription-coupled DNA repair.\",\n      \"method\": \"Site-specific photocrosslinking with unnatural amino acid, genetic deletion analysis, TCR assay\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — direct contact mapping by in vivo crosslinking at defined sites plus functional deletion analysis, single lab with two orthogonal methods\",\n      \"pmids\": [\"24813444\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Crystal structure of fission yeast RNA guanylyltransferase (GTase) bound to Spt5 CTD reveals a distinct docking site on the OB-fold domain that captures the Trp4 residue of the Spt5 nonapeptide repeat. A disruptive GTase mutation in the Spt5 CTD-binding site is synthetically lethal with mutations in the Pol2 CTD-binding site. Thr1 phosphorylation of Spt5 CTD inhibits GTase binding while Ser5-PO4 of Pol2 CTD is required.\",\n      \"method\": \"X-ray crystallography, genetic interaction (synthetic lethality), in vitro binding assays, mutagenesis\",\n      \"journal\": \"Genes & development\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — crystal structure plus genetic validation plus mutagenesis, multiple orthogonal approaches, defines Spt5 CTD code\",\n      \"pmids\": [\"24939935\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Fission yeast Cdk9/Pch1 (ortholog of metazoan P-TEFb CDK9) phosphorylates the Spt5 CTD specifically on threonine at position 1 (Thr1) within each nonapeptide repeat. CDK9 also phosphorylates the Pol II CTD Ser residues. Autophosphorylation of both Cdk9 and its cyclin partner Pch1 was documented.\",\n      \"method\": \"In vitro kinase assay with CTD peptides and truncation mutants, phosphoamino acid analysis, mutagenesis of kinase active site\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro kinase assay with site-specific mutagenesis and phosphoamino acid analysis, single lab\",\n      \"pmids\": [\"12904290\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Deletion of the S. pombe Spt5 CTD results in slow growth and aberrant morphology, exacerbated by Pol II CTD truncation and rescued by capping enzyme overexpression, demonstrating overlapping functional roles of the Spt5 and Pol II CTDs in capping enzyme recruitment. The Spt5 CTD T1A mutation abolishes Cdk9 phosphorylation without affecting capping enzyme binding, and has a distinct positive role in elongation.\",\n      \"method\": \"Genetic analysis (deletion, alanine scanning mutagenesis, synthetic interaction), capping enzyme overexpression rescue, 6-AU sensitivity\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — separation-of-function mutagenesis with multiple genetic assays, single lab\",\n      \"pmids\": [\"20231361\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Crystal structures of KOW1-Linker1 (K1L1) and KOW2-KOW3 domains of yeast Spt5 reveal that K1L1 displays a positively charged patch (PCP) that binds nucleic acids in vitro. The PCP is important for in vivo function and partially overlaps functionally with Spt4, suggesting KOW1 and Spt4 form functionally redundant upstream contacts during elongation.\",\n      \"method\": \"X-ray crystallography, in vitro nucleic acid binding assay, genetic growth assay\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — crystal structure plus biochemical nucleic acid binding plus genetic functional validation, single lab with three orthogonal methods\",\n      \"pmids\": [\"26217010\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Spt5 depletion in S. pombe causes RNAPII accumulation in the first ~500 bp of genes, widespread antisense transcription initiating in this barrier region, and reduced elongation rate genome-wide, demonstrating Spt5 is required for transcription past a 5'-proximal barrier and for suppression of antisense transcription.\",\n      \"method\": \"Auxin-inducible degron depletion, ChIP-seq, RNA-seq, NET-seq, MNase-seq\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genome-wide multi-method analysis with inducible depletion, four independent genome-wide approaches\",\n      \"pmids\": [\"28366642\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"Spt5 KOW4-KOW5 region is essential for promoter-proximal pausing, and KOW5 directly contacts the nascent transcript (RNA cross-linking). KOW2-3 domain mediates NELF recruitment to the elongation complex. KOW1 interaction with upstream DNA helix is required for DSIF association with the Pol II elongation complex.\",\n      \"method\": \"Reconstituted in vitro pausing assay with mutant DSIF, Drosophila nuclear extract complementation, RNA cross-linking\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro reconstitution with domain mutants and direct RNA crosslinking, multiple domain-function assignments, single lab\",\n      \"pmids\": [\"28213523\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"SPT5 directly interacts with MSL1 (of the Drosophila dosage compensation MSL complex) in vitro, and is required downstream of MSL complex chromatin recruitment for dosage compensation, providing mechanistic support for the elongation model of dosage compensation.\",\n      \"method\": \"Forward genetic screen, in vitro pulldown/interaction assay\",\n      \"journal\": \"PLoS genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — single in vitro pulldown and genetic epistasis, single lab\",\n      \"pmids\": [\"23209435\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Spt5 contains an acidic N-terminal tail (Spt5N) with a histone-binding motif required for viability in yeast. Spt5N is sandwiched between the downstream nucleosome and upstream DNA emerging from Pol II, and prevents loss of nucleosomal histones within actively transcribed regions, coupling processive transcription to histone capture and re-deposition.\",\n      \"method\": \"Structural analysis (cryo-EM context), genetic essentiality of Spt5N motif, histone occupancy assay by ChIP\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic essentiality of defined domain plus ChIP demonstration of histone loss phenotype, single lab with two orthogonal methods\",\n      \"pmids\": [\"35102600\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"ZWC complex (ZC3H4, WDR82, CK2) preferentially localizes at TSS of active genes via interaction of ZC3H4/WDR82 with S5p Pol II CTD, and phosphorylates the N-terminal acidic domain of SPT5. This phosphorylation suppresses divergent antisense transcription at gene promoters.\",\n      \"method\": \"Co-IP, ChIP-seq, knockdown (ZC3H4 depletion), in vitro kinase assay, antisense RNA quantification\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP and in vitro kinase assay with ChIP-seq phenotype, single lab\",\n      \"pmids\": [\"35325203\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Spt5 depletion in mouse B cells leads to loss of super-enhancer–promoter physical interaction and Igh gene expression, correlating strictly with loss of enhancer transcription. CRISPRa rescue of enhancer transcription in Spt5-depleted cells restored Igh gene expression, while histone H3K27 acetylation, chromatin accessibility, and Mediator/cohesin at the enhancer were unaffected.\",\n      \"method\": \"Acute Spt5 depletion, 4C/Hi-C (chromatin interaction), CRISPRa rescue, nascent transcription measurement, ChIP-seq\",\n      \"journal\": \"Nature genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — acute depletion with CRISPRa rescue experiment, multiple orthogonal chromatin and transcription assays\",\n      \"pmids\": [\"32251373\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Spt5 depletion in mouse embryonic fibroblasts does not cause global elongation defects or decreased rates, but causes dislodging of a fraction of Pol II complexes during elongation specifically at 15–20 kb from the promoter, coinciding with the transition to maximum elongation speed. Long genes show greater dependency on Spt5 for optimal elongation efficiency than short genes.\",\n      \"method\": \"Spt5 depletion (auxin-inducible degron in MEFs), genome-wide elongation rate measurement, ChIP-seq\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — inducible depletion with genome-wide elongation rate measurements, single lab with well-controlled quantitative approach\",\n      \"pmids\": [\"29514850\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Spt5 modulates cotranscriptional spliceosome assembly in S. cerevisiae: Spt5 depletion impairs U5 snRNP accumulation at intron-containing genes, reducing stable cotranscriptional spliceosome assembly. Spt5 co-immunoprecipitates with core spliceosomal proteins and all spliceosomal snRNAs.\",\n      \"method\": \"Auxin-inducible degron depletion, ChIP (U5 snRNP), co-immunoprecipitation with spliceosomal snRNAs, splicing assay\",\n      \"journal\": \"RNA\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — inducible depletion with Co-IP of spliceosomal components and ChIP, single lab\",\n      \"pmids\": [\"31289129\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"ARMC5 is identified as a CUL3 adaptor required for VCP/p97-dependent degradation of SPT5-depleted, promoter-proximal Pol II. ARMC5 targets promoter-proximal Pol II in a BTB domain-dependent manner, and interaction between ARMC5 and Pol II requires CDK9, supporting a phospho-dependent degradation model of defective promoter-proximal Pol II.\",\n      \"method\": \"Unbiased proteomic screening (mass spectrometry), genome-wide ChIP-seq, biochemical interaction assay, genetic domain analysis (BTB domain)\",\n      \"journal\": \"Science advances\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — proteomic screen plus ChIP-seq plus biochemical validation, multiple orthogonal approaches, single lab\",\n      \"pmids\": [\"39854452\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Phosphorylations of SPT5 in three regions—the KOW4-5 linker, CTR1, and CTR2—coordinately control pause release, elongation speed, and termination. CTR1 phosphorylation loss slows elongation; simultaneous CTR2 loss partially reverses this but adds effects on splicing and termination. Pausing is unaffected by CTR1 loss but increased by CTR2 loss.\",\n      \"method\": \"CRISPR phospho-mutant knock-in in human HCT116 cells, TT-seq (elongation rate), ChIP-seq, splicing and termination assays\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — endogenous phospho-mutants in human cells with genome-wide elongation rate, ChIP, splicing and termination readouts, multiple orthogonal methods\",\n      \"pmids\": [\"40250441\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"KOW4 domain of Spt5 promotes Pol II pausing through contact with nascent RNA, while the KOW2-3 domain mediates NELF recruitment to the elongation complex. KOW1 interaction with upstream DNA helix is required for DSIF association with Pol II. A short helical motif in the NGN domain contacts the non-template DNA strand and facilitates pausing.\",\n      \"method\": \"Purified in vitro pausing assay, Drosophila nuclear extract complementation, RNA cross-linking analysis, in vivo Drosophila viability assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro reconstitution with domain mutants, RNA crosslinking, and in vivo viability confirmation, multiple orthogonal methods\",\n      \"pmids\": [\"37517697\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Xrn2 (RNA exonuclease, torpedo termination factor) engages with Pol II forming a stable complex, and Spt5 stimulates Xrn2 activity to ensure efficient degradation of nascent RNA leading to Pol II dislodgement. Spt5 is also a key factor attenuating expression of non-coding transcripts, coordinates pre-mRNA splicing, and 3'-end processing.\",\n      \"method\": \"Co-immunoprecipitation (Xrn2-Pol II complex), in vitro Xrn2 activity assay, RNA-seq, splicing assay, termination assay\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro activity assay demonstrating Spt5 stimulates Xrn2 plus Co-IP and multiple genome-wide readouts, single lab with multiple orthogonal methods\",\n      \"pmids\": [\"39746995\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"SEC (super elongation complex) induces SPT5 phase transition into elongation droplets during early elongation. SPT5's disordered domain is required for pause release and gene activation. Depletion of SEC increases SPT5 pausing clusters. Disease-associated SEC mutations impair phase properties of elongation droplets.\",\n      \"method\": \"Live-cell imaging of condensates, phase separation assay in vitro, SEC depletion, fluorescence microscopy\",\n      \"journal\": \"EMBO reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — phase separation/condensate assay with SEC depletion, single lab, emerging methodology\",\n      \"pmids\": [\"36629390\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"SPT5 is required for efficient expression of HSV-1 replication-dependent γ2 late genes; siRNA knockdown of SPT5 (but not NELF-E) specifically inhibits HSV-1 late gene expression. DRB treatment reduces co-immunoprecipitation of viral ICP27 with SPT5, suggesting SPT5-ICP27 interaction is relevant for late gene expression.\",\n      \"method\": \"siRNA knockdown, RT-qPCR, co-immunoprecipitation\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — siRNA with specific phenotype and Co-IP, single lab\",\n      \"pmids\": [\"28743741\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1997,\n      \"finding\": \"Human SUPT5H protein is reversibly phosphorylated during mitosis, as demonstrated by purification from HeLa cells and analysis of mitotic phosphorylation state.\",\n      \"method\": \"Protein purification from HeLa cells, phosphorylation state analysis in mitotic vs. interphase cells\",\n      \"journal\": \"FEBS letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single biochemical analysis of mitotic phosphorylation, no functional consequence determined, single lab\",\n      \"pmids\": [\"9199507\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"O-GlcNAcase (OGA) physically associates with SPT5 and TRIM28/KAP1/TIF1β, forming a purified OGA-SPT5-TIF1β complex with elongation properties in vitro. OGA activity is required for elongation in crude nuclear extract but inhibits elongation in a purified system.\",\n      \"method\": \"Co-immunoprecipitation, in vitro transcription elongation assay, ChIP-seq, protein complex purification\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — purified complex with in vitro elongation assay and ChIP-seq, single lab with multiple methods\",\n      \"pmids\": [\"27601472\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"LEDGF/p75 is enriched at paused promoters and prevents phosphorylation of the SPT5 PRD/CTR1 by the super elongation complex (SEC). Deletion of the LEDGF IBD domain increases SEC occupancy and SPT5 PRD phosphorylation at promoters, leading to increased pause release. LEDGF and SEC function cooperatively on distinct SPT5 domains to control the pausing-to-elongation transition.\",\n      \"method\": \"ChIP-seq, phosphorylation assay, domain deletion analysis, CUT&RUN\",\n      \"journal\": \"Science advances\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — ChIP-seq with domain deletion analysis and phosphorylation measurements, single lab\",\n      \"pmids\": [\"39823345\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Crystal structure of fission yeast RNA triphosphatase Pct1 in complex with Spt5 CTD reveals two CTD docking sites on the Pct1 homodimer engaging TPAWN segments. Threonine phosphorylation of the Spt5 CTD antagonizes Pct1 binding, establishing a binary Spt5 CTD code where Thr1-PO4 is an 'off' switch for capping enzyme recruitment.\",\n      \"method\": \"X-ray crystallography, in vitro binding assay, phosphorylation competition assay\",\n      \"journal\": \"RNA\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — crystal structure plus biochemical binding assay with phosphomimetic analysis, single lab with multiple orthogonal methods\",\n      \"pmids\": [\"25414009\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Spt5 CTD Thr1 phosphorylation positively regulates histone H3K4 methylation while having minimal effect on H3K36 methylation in fission yeast. Combined Spt5 and Rpb1 CTD mutations have additive effects on H3K36me, suggesting overlapping roles. Pol II Ser2 phosphorylation by Lsk1/Cdk12 positively regulates H3K36me but negatively regulates H3K4me.\",\n      \"method\": \"Phospho-site mutagenesis (alanine substitutions), histone modification western blot and ChIP, genetic epistasis\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — systematic CTD phospho-site mutagenesis with histone modification readouts, single lab\",\n      \"pmids\": [\"26275777\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Spt5 depletion extends Pol II pausing zones beyond the canonical 40–100 bp window to 0.3–3 kb into genes. Phosphomimetic substitutions in CTR1 diminish pausing throughout genes, while mutations preventing phosphorylation of the Spt5 RNA-binding linker (KOW4-5 domain) strengthen pausing, revealing distinct phospho-isoforms that set the balance between pausing and elongation.\",\n      \"method\": \"Spt5 depletion with phospho-mutant rescue, eNET-seq (elongating polymerase mapping), PTEFb inhibition\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genome-wide eNET-seq with phospho-mutant rescue and kinase inhibition, multiple orthogonal approaches defining phospho-isoform functions\",\n      \"pmids\": [\"36206739\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"SUPT5H/SPT5 is an essential, universally conserved transcription elongation factor that forms the DSIF complex with SPT4; it directly associates with RNA Pol II via its NGN and KOW domains to regulate processive elongation, stabilizes promoter-proximal Pol II against ubiquitin-mediated degradation (via Cullin 3-ARMC5), promotes pause release and elongation through CDK9-dependent phosphorylation of its linker and CTR1/CTR2 repeat domains (which are dephosphorylated by PNUTS-PP1 to trigger Pol II deceleration and Xrn2-mediated termination), recruits the PAF complex through its phospho-CTR interacting with Rtf1/Plus3, recruits mRNA capping enzymes to nascent transcripts, suppresses divergent antisense transcription, facilitates cotranscriptional splicing, and is regulated post-translationally by PRMT1/PRMT5 arginine methylation and by CK2-mediated phosphorylation of its N-terminal acidic domain.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"SUPT5H/SPT5 is an essential, deeply conserved transcription elongation factor that, together with SPT4, forms the DSIF complex and governs the processivity of RNA polymerase II across the transcription cycle [#0, #2]. SPT5 binds Pol II directly through its central NusG N-terminal homology (NGN) and KOW domains—with KOW4-5 contacting the Rpb4/7 subcomplex and Rpb1/Rpb2 clamp, KOW5 contacting nascent RNA, and KOW1 engaging upstream DNA to anchor DSIF on the elongation complex [#22, #28]—while SPT4 binds the NGN domain through an acid-dipole interface that maintains KOW conformation [#12]. DSIF exerts dual control over Pol II: it enforces promoter-proximal pausing (in part through KOW2-3-mediated NELF recruitment) and is also required for processive elongation, with depletion causing loss of paused Pol II and processivity defects that are most pronounced in long genes [#0, #28, #16, #33]. This balance is set by phosphorylation: P-TEFb/CDK9 phosphorylates the C-terminal repeat (CTR) and the KOW4-5 linker to drive pause release, and coordinated phospho-states of the linker, CTR1, and CTR2 tune elongation speed, pausing, splicing, and termination [#3, #24, #16, #36, #46]. The phosphorylated Spt5 CTR provides a docking platform that recruits the PAF complex via Rtf1's Plus3 domain and licenses downstream histone modifications including H2B monoubiquitination and H3K4/K36 methylation [#9, #10, #11, #21]; the CTR nonapeptide repeats also recruit mRNA capping enzymes through a Thr1-phosphorylation-controlled binary code [#8, #23, #44]. At gene 3' ends, PNUTS-PP1 dephosphorylates Spt5 to decelerate Pol II and license Xrn2-mediated torpedo termination, with Spt5 directly stimulating Xrn2 nuclease activity [#13, #38]. SPT5 stabilizes promoter-proximal Pol II against Cullin 3/ARMC5- and VCP/p97-mediated ubiquitin-proteasomal degradation of RPB1 in a CDK9-dependent manner [#15, #35], suppresses divergent and antisense transcription [#27, #31], facilitates cotranscriptional spliceosome assembly [#34], couples transcription to histone retention via an acidic N-terminal tail [#30], and is required for enhancer transcription and super-enhancer-promoter contacts [#32]. SPT5 is additionally co-opted in specialized contexts including MYC-driven elongation [#14], AID-dependent class switch recombination [#19], and herpesvirus late gene expression [#40], and is regulated post-translationally by PRMT1/PRMT5 arginine methylation [#5] and CK2-family phosphorylation of its N-terminal acidic domain [#31].\",\n  \"teleology\": [\n    {\n      \"year\": 1991,\n      \"claim\": \"Established that SPT5 is an essential nuclear protein, framing it as a broadly required transcription factor rather than a gene-specific regulator.\",\n      \"evidence\": \"Null mutant lethality and immunofluorescence of an SPT5-\\u03b2-galactosidase fusion in yeast\",\n      \"pmids\": [\"1840633\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not define molecular function or interaction partners\", \"No mechanism linking essentiality to transcription\"]\n    },\n    {\n      \"year\": 1998,\n      \"claim\": \"Identified SPT5/SPT4 as the DSIF complex and resolved its paradoxical dual role in restraining and stimulating Pol II elongation, defining SPT5 as a core elongation factor.\",\n      \"evidence\": \"Biochemical purification from HeLa extracts with in vitro transcription assays, plus yeast co-IP and allele-specific genetic suppression by Pol II mutants\",\n      \"pmids\": [\"9450929\", \"9450930\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Domain basis of Pol II contact not yet mapped\", \"Mechanistic switch between positive and negative roles unresolved\"]\n    },\n    {\n      \"year\": 2000,\n      \"claim\": \"Mapped the modular domain architecture of SPT5 and identified CTR1 as a P-TEFb substrate, providing the first link between SPT5 phosphorylation and elongation control.\",\n      \"evidence\": \"Domain deletion in vitro transcription and recombinant P-TEFb phosphorylation assays; polytene/ChIP localization to elongating Pol II in Drosophila\",\n      \"pmids\": [\"10757782\", \"11040217\", \"11040216\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Phosphorylation sites within CTR not defined\", \"Downstream effectors of phospho-CTR unknown\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Defined SPT5 as a stage-specific elongation factor required in late elongation to prevent premature RNA dissociation, refining when in the cycle SPT5 acts.\",\n      \"evidence\": \"In vitro three-stage HIV-1 transcription with immunodepletion and chase experiments\",\n      \"pmids\": [\"11809800\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In vitro system may not capture chromatin context\", \"Did not connect to physiological terminator architecture\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Connected the Spt5 CTD to mRNA capping and identified arginine methylation as a regulatory input, establishing SPT5 as a hub coupling elongation to co-transcriptional RNA processing.\",\n      \"evidence\": \"Two-hybrid/in vitro binding of CTD to capping enzymes; PRMT1/PRMT5 in vitro methylation with arginine mutagenesis; CDK9 phosphorylation of CTD Thr1\",\n      \"pmids\": [\"11893740\", \"12718890\", \"12904290\", \"12556496\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Functional consequence of methylation in vivo not quantified\", \"Capping-recruitment regulation by phosphorylation not yet structurally resolved\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Demonstrated that kinase-dependent phosphorylation of the Spt5 CTR recruits the PAF complex and licenses elongation-coupled histone modifications, defining a phospho-CTR-to-chromatin signaling axis.\",\n      \"evidence\": \"Analog-sensitive Bur1 kinase chemical genetics, in vitro kinase assays on isolated elongation complexes, ChIP, and histone modification analysis\",\n      \"pmids\": [\"19581288\", \"19365074\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct CTR-PAF binding interface not resolved at this stage\", \"Ordering of H2B ubiquitination relative to H3 methylation unclear\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Provided the structural basis for SPT4-SPT5 assembly, explaining how SPT4 maintains the elongation-competent conformation of SPT5 KOW domains.\",\n      \"evidence\": \"Crystal structure of Spt4-NGN with interface mutagenesis and archaeal complex reconstitution\",\n      \"pmids\": [\"19000817\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not capture SPT5 in the context of Pol II\", \"KOW domain functions inferred, not directly tested\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Defined at atomic resolution how phosphorylated Spt5 CTR is read by Rtf1/Plus3, establishing the molecular recruitment mechanism for the PAF complex.\",\n      \"evidence\": \"X-ray structure of Rtf1 Plus3 with phospho-Spt5 repeat, in vitro binding mutagenesis, and ChIP; complemented by direct Rtf1-CTR interaction mapping\",\n      \"pmids\": [\"24101474\", \"23775116\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Stoichiometry of multivalent CTR-PAF engagement unresolved\", \"Kinase specificity setting the phospho-mark in human cells not addressed\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Mapped SPT5-Pol II contacts at residue resolution and decoded the capping-enzyme CTD recognition code, showing how phosphorylation toggles processing factor recruitment.\",\n      \"evidence\": \"Site-specific photocrosslinking with unnatural amino acids mapping KOW4-5/Rpb contacts; crystal structures of guanylyltransferase-CTD with synthetic-lethality validation\",\n      \"pmids\": [\"24813444\", \"24939935\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Dynamics of contact remodeling during the cycle not captured\", \"Coupling of CTD code to elongation rate not directly measured\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Broadened the SPT5 functional repertoire to Pol I association, mRNA localization, and AID-dependent class switch recombination, indicating SPT5 acts as a general elongation scaffold co-opted for specialized outcomes.\",\n      \"evidence\": \"Far Western direct binding to Pol I/II subunits; co-IP linking She2p to elongating Pol II; shRNA screen plus co-IP/ChIP-seq for AID at stalled Pol II\",\n      \"pmids\": [\"21467036\", \"20713510\", \"20887897\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Pol I role mechanistically distinct from elongation not detailed\", \"She2p link single-lab without structural detail\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Resolved KOW domain structures and the CTD capping code in detail, showing nucleic-acid-binding surfaces and Thr1 phosphorylation as a binary off-switch for capping enzyme recruitment.\",\n      \"evidence\": \"Crystal structures of KOW1-Linker1/KOW2-3 and of Pct1-CTD with binding/competition assays; phospho-site mutagenesis linking CTD Thr1 to H3K4 methylation\",\n      \"pmids\": [\"26217010\", \"25414009\", \"26275777\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Redundancy between KOW1 PCP and Spt4 not fully quantified in vivo\", \"Whether the human CTR uses an identical code not established here\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Genome-wide depletion studies established SPT5 as required to overcome a 5'-proximal elongation barrier and to suppress pervasive antisense transcription, defining its role in transcription directionality and progression.\",\n      \"evidence\": \"Auxin-inducible degron depletion in S. pombe with ChIP-seq, RNA-seq, NET-seq, MNase-seq; in vitro reconstituted pausing with KOW domain mutants assigning NELF recruitment and nascent-RNA contacts\",\n      \"pmids\": [\"28366642\", \"28213523\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Barrier composition not molecularly defined\", \"How SPT5 distinguishes sense from antisense initiation unclear\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Defined SPT5 dephosphorylation as the trigger for Pol II deceleration and torpedo termination, and quantified SPT5's contribution to elongation processivity in long genes.\",\n      \"evidence\": \"Genome-wide elongation-rate measurement with PNUTS-PP1 separation-of-function mutation; auxin-degron depletion in MEFs with elongation rate mapping; MYC-SPT5 transfer mechanism by MS/Co-IP/ChIP-seq\",\n      \"pmids\": [\"31677974\", \"29514850\", \"30928206\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Phosphatase site specificity on Spt5 not fully resolved\", \"MYC sequestration model not extended to other oncogenic contexts\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Showed SPT5 actively protects promoter-proximal Pol II from ubiquitin-proteasomal destruction and is required for pause establishment and release, distinguishing its role from NELF.\",\n      \"evidence\": \"Auxin- and dTAG-inducible depletion with ubiquitination assays, Cullin 3/VCP/CDK9 dependency, PRO-seq/ChIP-seq/ATAC-seq, and phospho-mutant analysis of Ser666\",\n      \"pmids\": [\"34480849\", \"34534457\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"E3 adaptor identity not yet defined at this stage\", \"Coupling between Pol II protection and pause release mechanism incomplete\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Refined the phospho-isoform logic of pausing versus elongation and revealed SPT5's acidic N-tail in histone retention and antisense suppression, expanding its chromatin-coupling roles.\",\n      \"evidence\": \"eNET-seq with CTR1/linker phospho-mutant rescue; cryo-EM-context analysis with histone occupancy ChIP for Spt5N; ZWC (ZC3H4/WDR82/CK2) in vitro kinase and ChIP-seq; super-enhancer 4C/Hi-C with CRISPRa rescue\",\n      \"pmids\": [\"36206739\", \"35102600\", \"35325203\", \"32251373\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Relative contribution of distinct phospho-isoforms across gene classes not unified\", \"ZWC-SPT5 axis confirmed in single lab\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Identified ARMC5 as the CUL3 adaptor for promoter-proximal Pol II degradation, dissected coordinated CTR1/CTR2/linker phospho-control, and showed SPT5 directly stimulates Xrn2 to drive termination, integrating the elongation-to-termination program.\",\n      \"evidence\": \"Proteomic screen with BTB-domain/CDK9-dependent ARMC5 validation; CRISPR phospho-mutant knock-ins in HCT116 with TT-seq/ChIP-seq; in vitro Xrn2 activity assays with Co-IP and genome-wide readouts\",\n      \"pmids\": [\"39854452\", \"40250441\", \"39746995\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How phospho-marks are spatially ordered across the gene not fully resolved\", \"Direct structure of SPT5-Xrn2 stimulation absent\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How the full set of SPT5 phosphorylation marks, arginine methylation, and condensate/phase behavior are integrated kinetically to switch SPT5 between pausing, elongation, processing, and termination across distinct gene architectures remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No unified quantitative model linking each PTM to a defined cycle step\", \"Condensate-based regulation (SEC/LEDGF) characterized only in single labs\", \"Crosstalk between methylation and phosphorylation in vivo undefined\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0003723\", \"supporting_discovery_ids\": [28, 37, 26]},\n      {\"term_id\": \"GO:0003677\", \"supporting_discovery_ids\": [26, 37]},\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [11, 21, 8]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [0, 13, 38]},\n      {\"term_id\": \"GO:0140110\", \"supporting_discovery_ids\": [0, 3, 16]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [2]},\n      {\"term_id\": \"GO:0000228\", \"supporting_discovery_ids\": [4]},\n      {\"term_id\": \"GO:0005654\", \"supporting_discovery_ids\": [4, 1]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-74160\", \"supporting_discovery_ids\": [0, 1, 16, 27]},\n      {\"term_id\": \"R-HSA-4839726\", \"supporting_discovery_ids\": [9, 10, 30, 45]},\n      {\"term_id\": \"R-HSA-8953854\", \"supporting_discovery_ids\": [8, 34, 38, 20]},\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [15, 35]}\n    ],\n    \"complexes\": [\"DSIF (SPT4-SPT5)\"],\n    \"partners\": [\"SUPT4H1\", \"POLR2A\", \"RTF1\", \"XRN2\", \"MYC\", \"AICDA\", \"ARMC5\", \"MSL1\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":8,"faith_total":8,"faith_pct":100.0}}