{"gene":"PIH1D1","run_date":"2026-04-28T19:45:44","timeline":{"discoveries":[{"year":2008,"finding":"Pih1/Nop17 (yeast ortholog of PIH1D1) forms part of the R2TP complex (with Rvb1, Rvb2, and Tah1) and this complex is required for correct accumulation of box C/D and box H/ACA small nucleolar ribonucleoproteins; Hsp90 together with Tah1 stabilizes the otherwise unstable Pih1 protein.","method":"Genetic interaction screens, co-immunoprecipitation, yeast genetics, in vivo snoRNA accumulation assays","journal":"The Journal of cell biology","confidence":"High","confidence_rationale":"Tier 2 — reciprocal Co-IP, functional snoRNP accumulation assays, multiple orthogonal methods, highly cited foundational study","pmids":["18268103"],"is_preprint":false},{"year":2010,"finding":"The Pih1-Tah1 heterodimer (yeast orthologs) binds Hsp90 with similar affinity and stoichiometry as Tah1 alone but inhibits Hsp90 ATPase activity; Pih1 alone is unstable and degraded from its N terminus, while the Pih1-Tah1 complex is stable. The region within Pih1 responsible for Tah1 interaction and Hsp90 ATPase inhibition was identified.","method":"Analytical ultracentrifugation, microcalorimetry (ITC), noncovalent mass spectrometry, ATPase assays","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — multiple rigorous biophysical methods, in vitro enzymatic assay, mutagenesis-guided domain mapping","pmids":["20663878"],"is_preprint":false},{"year":2011,"finding":"Tah1 (yeast ortholog of RPAP3) binds the C terminus of Pih1 through its C-helix and unstructured region; the C terminus of Pih1 destabilizes the protein in vitro and in vivo, whereas Tah1 binding forms a stable complex. NMR structure of Tah1 reveals two TPR motifs plus a C-helix binding the Hsp90 EEVD C-terminal motif via a two-carboxylate clamp.","method":"NMR structure determination, co-immunoprecipitation, in vitro binding assays, in vivo stability assays","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 — NMR structure with functional validation of binding and stability, multiple orthogonal methods","pmids":["22179618"],"is_preprint":false},{"year":2012,"finding":"The C terminus of Pih1 (yeast ortholog) contains multiple degron/destabilization elements including two intrinsically disordered regions; IDR2 mediates Tah1 binding. Pih1 N-terminal domain (residues 1–195/1–230) binds Rvb1/Rvb2 heterocomplex, and the sequence between the two disordered regions enhances this binding. Pih1(1–230) complements full-length Pih1 function at 37°C.","method":"Site-directed mutagenesis, in vitro and in vivo stability assays, co-immunoprecipitation, yeast complementation","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 — mutagenesis combined with in vivo and in vitro binding assays, multiple orthogonal methods","pmids":["23139418"],"is_preprint":false},{"year":2014,"finding":"PIH1D1 contains a phosphopeptide-binding domain (PIH-N) that preferentially binds highly acidic phosphorylated proteins. A co-crystal structure of PIH-N with a TEL2 phosphopeptide reveals that Lys57 and Lys64 in PIH1D1, together with a conserved DpSDD motif in TEL2, are essential for binding. Proteomic analysis identified multiple R2TP substrates recruited via this phosphorylation-dependent mechanism (CK2 phosphorylation-dependent recognition).","method":"X-ray crystallography (co-crystal structure), site-directed mutagenesis, proteomic/MS interactome analysis, in vitro binding assays","journal":"Cell reports","confidence":"High","confidence_rationale":"Tier 1 — crystal structure plus mutagenesis plus proteomic validation, two independent papers confirm same mechanism","pmids":["24656813"],"is_preprint":false},{"year":2014,"finding":"PIH1D1 contains a domain specific for binding CK2 phosphorylation sites, mediating recruitment of TEL2 (and the TTT complex) to the Hsp90/R2TP system; structural and biochemical analysis defined Hsp90-Tah1-Pih1, Hsp90-Spagh (RPAP3), and PIH1D1-TEL2 complex architectures.","method":"X-ray crystallography (multiple complex structures), biochemical binding assays, isothermal titration calorimetry","journal":"Structure","confidence":"High","confidence_rationale":"Tier 1 — crystal structures of multiple complexes with functional biochemical validation, confirms findings of PMID:24656813","pmids":["24794838"],"is_preprint":false},{"year":2013,"finding":"Human PIH1D1 specifically co-immunoprecipitates Raptor (mTORC1-specific) but not Rictor (mTORC2-specific); knockdown of PIH1D1 decreases mTORC1 assembly, S6 kinase phosphorylation, and rRNA transcription without affecting mTORC2.","method":"Co-immunoprecipitation, siRNA knockdown, S6K phosphorylation assay, rRNA transcription assay","journal":"FEBS letters","confidence":"Medium","confidence_rationale":"Tier 2 — Co-IP plus functional KD phenotype, but single lab with moderate methods","pmids":["24036451"],"is_preprint":false},{"year":2012,"finding":"Human PIH1 (PIH1D1) directly interacts with histone H4 and recruits the Brg1-SWI/SNF complex (via SNF5) to rRNA gene promoters, mediates DNase I-hypersensitive chromatin remodeling at the core promoter, promotes RNA Pol I occupancy and rRNA transcription initiation, and displaces TIP5 (a NoRC silencing component) from the core region.","method":"Co-immunoprecipitation, ChIP assays, DNase I hypersensitivity assay, siRNA knockdown, in vitro binding","journal":"Journal of molecular cell biology","confidence":"Medium","confidence_rationale":"Tier 2 — multiple ChIP and functional assays, single lab","pmids":["22368283"],"is_preprint":false},{"year":2009,"finding":"PIH1D1 interacts with SNF5 (a core subunit of the SWI/SNF chromatin remodeling complex) and stabilizes SNF5 by attenuating its proteasome-mediated degradation.","method":"Co-immunoprecipitation, cycloheximide chase, proteasome inhibitor (MG132) treatment, plasmid overexpression","journal":"Acta Academiae Medicinae Sinicae","confidence":"Low","confidence_rationale":"Tier 3 — single lab, single method set, limited mechanistic depth","pmids":["20078948"],"is_preprint":false},{"year":2010,"finding":"PIH1D1 interacts with both RPAP3 and Monad (Reptin/RUVBL2) in human cells; siRNA-mediated knockdown of PIH1D1 enhances doxorubicin-induced apoptosis and caspase-3 activation, placing PIH1D1 as a modulator of the apoptosis pathway.","method":"Co-immunoprecipitation, siRNA knockdown, caspase-3 activation assay","journal":"Biochemical and biophysical research communications","confidence":"Low","confidence_rationale":"Tier 3 — single Co-IP and KD phenotype, no pathway placement beyond apoptosis modulation","pmids":["21078300"],"is_preprint":false},{"year":2012,"finding":"RPAP3 isoform 1 (but not isoform 2) interacts with PIH1D1 to form the R2TP complex; knockdown of RPAP3 isoform 1 downregulates PIH1D1 protein level without affecting PIH1D1 mRNA, indicating post-transcriptional stabilization of PIH1D1 by RPAP3 isoform 1.","method":"Co-immunoprecipitation, siRNA knockdown, RT-PCR, Western blot","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 3 + Moderate — co-IP plus mRNA/protein level dissection provides mechanistic insight into complex composition and PIH1D1 stability","pmids":["23159623"],"is_preprint":false},{"year":2015,"finding":"Yeast Pih1 (PIH1D1 ortholog) directly interacts with snoRNP assembly factor Rsa1p (NUFIP1) and snoRNP core protein Nop58p; these two interactions are mutually exclusive. NMR and ITC mapping identified the binding domains. Tah1p (RPAP3) can stabilize Pih1p in the absence of Hsp82 (Hsp90) activity during stationary phase, via direct contacts between the Pih1p CS domain and Tah1p C-terminal tail forming two intermolecular β-sheets.","method":"NMR structure, ITC, co-expression in E. coli, in vivo and in vitro binding assays","journal":"Journal of molecular biology","confidence":"High","confidence_rationale":"Tier 1 — NMR solution structure plus ITC plus co-expression reconstitution, multiple orthogonal methods","pmids":["26210662"],"is_preprint":false},{"year":2016,"finding":"Yeast Pih1 (PIH1D1 ortholog) undergoes ubiquitin-independent proteasomal degradation mediated by direct interaction between the Pih1 C-terminal fragment and the C-terminal 30 amino acids of proteasome subunit Rpn8; this interaction is specifically revealed when Hsp90 co-chaperone Tah1 is depleted.","method":"Co-immunoprecipitation, truncation mutagenesis, in vitro and in vivo degradation assays, GFP-fusion reporter degradation assay","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 — in vitro and in vivo degradation assays with mutagenesis, identifying specific proteasome subunit mediating ubiquitin-independent degradation","pmids":["27053109"],"is_preprint":false},{"year":2015,"finding":"Yeast Nop17/Pih1 (PIH1D1 ortholog) interacts with Nop58 in an ATP-dependent manner with respect to Rvb1/2; the R2TP complex reduces Nop58 affinity for snoRNA, facilitating binding of other snoRNP subunits during box C/D snoRNP assembly.","method":"In vitro binding assays, domain mapping, ATP dependency experiments","journal":"BMC molecular biology","confidence":"Medium","confidence_rationale":"Tier 3 — in vitro binding with domain mapping, single lab, moderate mechanistic resolution","pmids":["25888478"],"is_preprint":false},{"year":2025,"finding":"In Trypanosoma brucei, PIH1D1 (a DNAAF PIH-family protein) concentrates at co-translational assembly sites on translating outer dynein arm heavy chains (HCs); loss of PIH1D1 reduces HC protein levels and leaves the IC-LC complex stranded in the cytoplasm, indicating PIH1D1 generates specialized compartments for co-translational folding of HCs and their assembly with other ODA subunits.","method":"Live imaging, genetic knockout, immunofluorescence, ribosome profiling/co-translational assembly assays in T. brucei","journal":"bioRxiv","confidence":"Low","confidence_rationale":"Tier 3 — preprint, single organism model distant from mammalian system, no peer review","pmids":["bio_10.1101_2025.07.26.666928"],"is_preprint":true}],"current_model":"PIH1D1 is the substrate-recognition subunit of the R2TP co-chaperone complex (with RPAP3/Tah1, RUVBL1/Rvb1, and RUVBL2/Rvb2) that bridges client proteins to Hsp90: its N-terminal PIH-N domain binds CK2-phosphorylated DpSDD motifs on substrates such as TEL2 (defined by co-crystal structure and mutagenesis), its C-terminal CS domain interacts with RPAP3 to form a stable heterodimer that inhibits Hsp90 ATPase activity, and together the complex directs assembly of box C/D and H/ACA snoRNPs, mTORC1, RNA Pol II, and PIKK complexes; when not protected by RPAP3/Hsp90, PIH1D1 is degraded via ubiquitin-independent proteasomal degradation mediated by direct binding to proteasome subunit Rpn8."},"narrative":{"teleology":[{"year":2008,"claim":"Identification of Pih1 as a core subunit of the R2TP complex established that an Hsp90-associated co-chaperone machinery is required for snoRNP biogenesis, answering why box C/D and H/ACA snoRNP accumulation depends on Hsp90.","evidence":"Genetic interaction screens, reciprocal Co-IP, and snoRNA accumulation assays in S. cerevisiae","pmids":["18268103"],"confidence":"High","gaps":["Mechanism by which R2TP remodels snoRNP precursors was unknown","Human complex composition unverified at this stage","Substrate recognition mode of Pih1 undefined"]},{"year":2010,"claim":"Biophysical characterization of the Pih1–Tah1 heterodimer revealed that Pih1 is inherently unstable and that the heterodimer inhibits Hsp90 ATPase activity, establishing that R2TP modulates the chaperone cycle rather than passively recruiting Hsp90.","evidence":"Analytical ultracentrifugation, ITC, noncovalent mass spectrometry, and ATPase assays with purified yeast proteins","pmids":["20663878"],"confidence":"High","gaps":["Structural basis of Pih1–Tah1 interaction not yet resolved","Functional consequence of ATPase inhibition on substrate assembly unclear"]},{"year":2011,"claim":"NMR structure of Tah1 and mapping of its Pih1-binding interface showed that Tah1 engages Pih1's destabilizing C-terminus to form a stable complex, explaining how R2TP integrity is maintained.","evidence":"NMR structure determination with binding and stability assays in yeast","pmids":["22179618"],"confidence":"High","gaps":["Full-length Pih1 structure unavailable","Role of intrinsically disordered regions in Pih1 function unresolved"]},{"year":2012,"claim":"Domain dissection of Pih1 identified that its N-terminal domain binds Rvb1/Rvb2 while disordered C-terminal elements contain degron and Tah1-binding functions, defining the modular architecture that separates substrate engagement from complex stabilization.","evidence":"Site-directed mutagenesis, Co-IP, and yeast complementation assays","pmids":["23139418"],"confidence":"High","gaps":["Identity of substrates recognized by the N-terminal domain not determined","Phosphorylation-dependent recognition not yet discovered"]},{"year":2012,"claim":"Demonstration that PIH1D1 binds histone H4, recruits Brg1–SWI/SNF to rDNA promoters, and promotes RNA Pol I occupancy expanded PIH1D1 function beyond snoRNP assembly to transcriptional regulation of rRNA genes.","evidence":"ChIP, DNase I hypersensitivity, Co-IP, and siRNA knockdown in human cells","pmids":["22368283"],"confidence":"Medium","gaps":["Whether this chromatin-remodeling role is R2TP-dependent or independent was not tested","Relevance to non-rDNA loci unknown","Single lab finding not independently confirmed"]},{"year":2012,"claim":"Showing that RPAP3 isoform 1 specifically stabilizes PIH1D1 at the post-transcriptional level confirmed the Pih1 stability paradigm in human cells and identified isoform specificity within the R2TP complex.","evidence":"Co-IP, siRNA knockdown with RT-PCR and Western blot in human cells","pmids":["23159623"],"confidence":"Medium","gaps":["Mechanism of post-transcriptional stabilization (folding vs. degradation shielding) not resolved","Isoform 2 function unexplored"]},{"year":2013,"claim":"Co-IP of PIH1D1 with Raptor but not Rictor, and reduced mTORC1 assembly upon PIH1D1 knockdown, established that R2TP specifically promotes mTORC1 but not mTORC2 assembly, broadening the client repertoire beyond snoRNPs.","evidence":"Co-IP, siRNA knockdown, S6K phosphorylation assay in human cells","pmids":["24036451"],"confidence":"Medium","gaps":["Direct versus indirect nature of PIH1D1–Raptor interaction not resolved","Whether TEL2/TTT mediates this interaction was not tested at this stage"]},{"year":2014,"claim":"Co-crystal structures of the PIH-N domain with a TEL2 phosphopeptide, together with proteomic identification of CK2-phosphorylated substrates, established the molecular basis of phospho-dependent substrate recognition — the central mechanistic step of how R2TP selects its clients.","evidence":"X-ray crystallography, site-directed mutagenesis, ITC, and proteomic/MS analysis","pmids":["24656813","24794838"],"confidence":"High","gaps":["Structural view of the full R2TP complex with a client protein not available","Not all proteomic hits validated as bona fide assembly substrates"]},{"year":2015,"claim":"NMR and ITC studies showing mutually exclusive binding of Pih1 to Rsa1 (NUFIP1) and Nop58 revealed a hand-off mechanism in snoRNP assembly, and showed that Tah1 can stabilize Pih1 independently of Hsp90 activity.","evidence":"NMR structure, ITC, and co-expression reconstitution in yeast/E. coli","pmids":["26210662"],"confidence":"High","gaps":["Whether the hand-off mechanism is conserved in human cells not tested","Kinetics of the hand-off in vivo not measured"]},{"year":2015,"claim":"ATP-dependent interaction of Pih1 with Nop58 via Rvb1/2 and reduced Nop58–snoRNA affinity by R2TP clarified how the complex actively remodels RNP intermediates rather than acting as a passive scaffold.","evidence":"In vitro binding assays with ATP dependency experiments in yeast","pmids":["25888478"],"confidence":"Medium","gaps":["Precise stoichiometry of the remodeling intermediate unknown","Whether Rvb1/2 ATPase activity is the driving force not directly demonstrated"]},{"year":2016,"claim":"Discovery that Pih1 undergoes ubiquitin-independent proteasomal degradation via direct binding to proteasome subunit Rpn8 explained the mechanistic basis of Pih1 instability and how R2TP disassembly leads to rapid PIH1D1 turnover.","evidence":"Co-IP, truncation mutagenesis, and in vitro/in vivo degradation assays in yeast","pmids":["27053109"],"confidence":"High","gaps":["Whether this ubiquitin-independent degradation pathway operates in mammalian cells not established","Structural basis of the Pih1–Rpn8 interaction not resolved"]},{"year":null,"claim":"A full structural view of the human R2TP complex engaged with a client during active assembly, and the relative contributions of PIH1D1's rDNA chromatin-remodeling function versus its canonical R2TP role, remain unresolved.","evidence":"","pmids":[],"confidence":"Low","gaps":["No cryo-EM or crystal structure of a complete human R2TP–client assembly","Relative in vivo importance of R2TP-independent functions (rDNA regulation, apoptosis modulation) not determined","Full catalog of bona fide PIH1D1-dependent assembly clients in human cells is incomplete"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[0,4,5,6]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[1,11]},{"term_id":"GO:0042393","term_label":"histone binding","supporting_discovery_ids":[7]}],"localization":[{"term_id":"GO:0005730","term_label":"nucleolus","supporting_discovery_ids":[7]},{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[7,8]}],"pathway":[{"term_id":"R-HSA-8953854","term_label":"Metabolism of RNA","supporting_discovery_ids":[0,11,13]},{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[4,5,12]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[6]},{"term_id":"R-HSA-74160","term_label":"Gene expression (Transcription)","supporting_discovery_ids":[7]}],"complexes":["R2TP"],"partners":["RPAP3","RUVBL1","RUVBL2","TEL2","NOP58","NUFIP1","SMARCB1","RPTOR"],"other_free_text":[]},"mechanistic_narrative":"PIH1D1 is the substrate-recognition subunit of the R2TP co-chaperone complex (with RPAP3/Tah1, RUVBL1, and RUVBL2) that couples Hsp90 chaperone activity to the assembly of macromolecular complexes including box C/D and H/ACA snoRNPs, mTORC1, and PIKK signaling complexes [PMID:18268103, PMID:24036451]. Its N-terminal PIH-N domain recognizes CK2-phosphorylated DpSDD motifs on substrates such as TEL2, as defined by co-crystal structures and mutagenesis of key residues Lys57 and Lys64, while its C-terminal CS domain heterodimerizes with RPAP3 and inhibits Hsp90 ATPase activity [PMID:24656813, PMID:24794838, PMID:20663878]. PIH1D1 is intrinsically unstable: RPAP3 binding stabilizes the protein post-translationally, and in the absence of this protection PIH1D1 undergoes ubiquitin-independent proteasomal degradation mediated by direct interaction of its C-terminal region with proteasome subunit Rpn8 [PMID:23159623, PMID:27053109]. PIH1D1 also participates in rRNA gene transcription by recruiting the Brg1–SWI/SNF chromatin remodeling complex to rDNA promoters, promoting RNA Pol I occupancy and displacing the silencing factor TIP5 [PMID:22368283]."},"prefetch_data":{"uniprot":{"accession":"Q9NWS0","full_name":"PIH1 domain-containing protein 1","aliases":["Nucleolar protein 17 homolog"],"length_aa":290,"mass_kda":32.4,"function":"Involved in the assembly of C/D box small nucleolar ribonucleoprotein (snoRNP) particles (PubMed:17636026). Recruits the SWI/SNF complex to the core promoter of rRNA genes and enhances pre-rRNA transcription (PubMed:22368283, PubMed:24036451). Mediates interaction of TELO2 with the R2TP complex which is necessary for the stability of MTOR and SMG1 (PubMed:20864032). Positively regulates the assembly and activity of the mTORC1 complex (PubMed:24036451)","subcellular_location":"Nucleus","url":"https://www.uniprot.org/uniprotkb/Q9NWS0/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/PIH1D1","classification":"Not Classified","n_dependent_lines":29,"n_total_lines":1208,"dependency_fraction":0.024006622516556293},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[{"gene":"POLR2A","stoichiometry":10.0},{"gene":"POLR2H","stoichiometry":10.0},{"gene":"POLR2B","stoichiometry":4.0},{"gene":"POLR2E","stoichiometry":4.0},{"gene":"FKBP5","stoichiometry":0.2},{"gene":"NOP58","stoichiometry":0.2},{"gene":"POLR1C","stoichiometry":0.2},{"gene":"POLR2J","stoichiometry":0.2},{"gene":"PTGES3","stoichiometry":0.2},{"gene":"RPAP2","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/search/PIH1D1","total_profiled":1310},"omim":[{"mim_id":"611480","title":"PIH1 DOMAIN-CONTAINING PROTEIN 1; PIH1D1","url":"https://www.omim.org/entry/611480"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Cytosol","reliability":"Approved"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/PIH1D1"},"hgnc":{"alias_symbol":["FLJ20643","Pih1","MOT48","DNAAF14"],"prev_symbol":["NOP17"]},"alphafold":{"accession":"Q9NWS0","domains":[{"cath_id":"-","chopping":"47-180","consensus_level":"high","plddt":88.928,"start":47,"end":180},{"cath_id":"2.60.40.790","chopping":"210-285","consensus_level":"high","plddt":86.3489,"start":210,"end":285}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9NWS0","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q9NWS0-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q9NWS0-F1-predicted_aligned_error_v6.png","plddt_mean":78.75},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=PIH1D1","jax_strain_url":"https://www.jax.org/strain/search?query=PIH1D1"},"sequence":{"accession":"Q9NWS0","fasta_url":"https://rest.uniprot.org/uniprotkb/Q9NWS0.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q9NWS0/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9NWS0"}},"corpus_meta":[{"pmid":"18268103","id":"PMC_18268103","title":"Molecular chaperone Hsp90 stabilizes Pih1/Nop17 to maintain R2TP complex activity that regulates snoRNA accumulation.","date":"2008","source":"The Journal of cell biology","url":"https://pubmed.ncbi.nlm.nih.gov/18268103","citation_count":150,"is_preprint":false},{"pmid":"24794838","id":"PMC_24794838","title":"Structural basis for phosphorylation-dependent recruitment of Tel2 to Hsp90 by Pih1.","date":"2014","source":"Structure (London, England : 1993)","url":"https://pubmed.ncbi.nlm.nih.gov/24794838","citation_count":76,"is_preprint":false},{"pmid":"24656813","id":"PMC_24656813","title":"Phosphorylation-dependent PIH1D1 interactions define substrate specificity of the R2TP cochaperone complex.","date":"2014","source":"Cell reports","url":"https://pubmed.ncbi.nlm.nih.gov/24656813","citation_count":71,"is_preprint":false},{"pmid":"20663878","id":"PMC_20663878","title":"The Pih1-Tah1 cochaperone complex inhibits Hsp90 molecular chaperone ATPase activity.","date":"2010","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/20663878","citation_count":60,"is_preprint":false},{"pmid":"22179618","id":"PMC_22179618","title":"Structure of minimal tetratricopeptide repeat domain protein Tah1 reveals mechanism of its interaction with Pih1 and Hsp90.","date":"2011","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/22179618","citation_count":42,"is_preprint":false},{"pmid":"24036451","id":"PMC_24036451","title":"PIH1D1 interacts with mTOR complex 1 and enhances ribosome RNA transcription.","date":"2013","source":"FEBS letters","url":"https://pubmed.ncbi.nlm.nih.gov/24036451","citation_count":25,"is_preprint":false},{"pmid":"26210662","id":"PMC_26210662","title":"Structure/Function Analysis of Protein-Protein Interactions Developed by the Yeast Pih1 Platform Protein and Its Partners in Box C/D snoRNP Assembly.","date":"2015","source":"Journal of molecular biology","url":"https://pubmed.ncbi.nlm.nih.gov/26210662","citation_count":25,"is_preprint":false},{"pmid":"21078300","id":"PMC_21078300","title":"PIH1D1, a subunit of R2TP complex, inhibits doxorubicin-induced apoptosis.","date":"2010","source":"Biochemical and biophysical research communications","url":"https://pubmed.ncbi.nlm.nih.gov/21078300","citation_count":23,"is_preprint":false},{"pmid":"23159623","id":"PMC_23159623","title":"RPAP3 splicing variant isoform 1 interacts with PIH1D1 to compose R2TP complex for cell survival.","date":"2012","source":"Biochemical and biophysical research communications","url":"https://pubmed.ncbi.nlm.nih.gov/23159623","citation_count":21,"is_preprint":false},{"pmid":"23139418","id":"PMC_23139418","title":"The stability of the small nucleolar ribonucleoprotein (snoRNP) assembly protein Pih1 in Saccharomyces cerevisiae is modulated by its C terminus.","date":"2012","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/23139418","citation_count":20,"is_preprint":false},{"pmid":"25888478","id":"PMC_25888478","title":"Nop17 is a key R2TP factor for the assembly and maturation of box C/D snoRNP complex.","date":"2015","source":"BMC molecular biology","url":"https://pubmed.ncbi.nlm.nih.gov/25888478","citation_count":19,"is_preprint":false},{"pmid":"33141819","id":"PMC_33141819","title":"Mutations in PIH proteins MOT48, TWI1 and PF13 define common and unique steps for preassembly of each, different ciliary dynein.","date":"2020","source":"PLoS genetics","url":"https://pubmed.ncbi.nlm.nih.gov/33141819","citation_count":15,"is_preprint":false},{"pmid":"22368283","id":"PMC_22368283","title":"Human PIH1 associates with histone H4 to mediate the glucose-dependent enhancement of pre-rRNA synthesis.","date":"2012","source":"Journal of molecular cell biology","url":"https://pubmed.ncbi.nlm.nih.gov/22368283","citation_count":13,"is_preprint":false},{"pmid":"27053109","id":"PMC_27053109","title":"The Proteasome Subunit Rpn8 Interacts with the Small Nucleolar RNA Protein (snoRNP) Assembly Protein Pih1 and Mediates Its Ubiquitin-independent Degradation in Saccharomyces cerevisiae.","date":"2016","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/27053109","citation_count":6,"is_preprint":false},{"pmid":"20078948","id":"PMC_20078948","title":"[Effect of PIH1D1 on the degradation of its binding protein SNF5].","date":"2009","source":"Zhongguo yi xue ke xue yuan xue bao. Acta Academiae Medicinae Sinicae","url":"https://pubmed.ncbi.nlm.nih.gov/20078948","citation_count":1,"is_preprint":false},{"pmid":"41424038","id":"PMC_41424038","title":"PIH1D1 and RPAP3, Components of the PAQosome: Emerging Roles in Cellular Physiology.","date":"2025","source":"Molecular and cellular biology","url":"https://pubmed.ncbi.nlm.nih.gov/41424038","citation_count":1,"is_preprint":false},{"pmid":"41819055","id":"PMC_41819055","title":"Methylated PIH1D1 as a Heart-Specific Biomarker for Anthracycline-Induced Cardiac Remodeling in Breast Cancer Patients.","date":"2026","source":"JACC. Basic to translational science","url":"https://pubmed.ncbi.nlm.nih.gov/41819055","citation_count":0,"is_preprint":false},{"pmid":null,"id":"bio_10.1101_2025.07.26.666928","title":"Spatiotemporal regulation of ciliary outer dynein arm biogenesis and the role of PIH homologs","date":"2025-07-30","source":"bioRxiv","url":"https://doi.org/10.1101/2025.07.26.666928","citation_count":0,"is_preprint":true},{"pmid":null,"id":"bio_10.1101_2025.09.11.675549","title":"CCDC103-mediated assembly of the R2C complex links RUVBL1-RUVBL2 to Primary Ciliary Dyskinesia","date":"2025-09-13","source":"bioRxiv","url":"https://doi.org/10.1101/2025.09.11.675549","citation_count":0,"is_preprint":true}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":9948,"output_tokens":3864,"usd":0.043902},"stage2":{"model":"claude-opus-4-6","input_tokens":7279,"output_tokens":2985,"usd":0.16653},"total_usd":0.210432,"stage1_batch_id":"msgbatch_01SUR8NDzVrNmyszWyJeCct7","stage2_batch_id":"msgbatch_01G7Yfutko3cDWzejrwH5AMx","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2008,\n      \"finding\": \"Pih1/Nop17 (yeast ortholog of PIH1D1) forms part of the R2TP complex (with Rvb1, Rvb2, and Tah1) and this complex is required for correct accumulation of box C/D and box H/ACA small nucleolar ribonucleoproteins; Hsp90 together with Tah1 stabilizes the otherwise unstable Pih1 protein.\",\n      \"method\": \"Genetic interaction screens, co-immunoprecipitation, yeast genetics, in vivo snoRNA accumulation assays\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal Co-IP, functional snoRNP accumulation assays, multiple orthogonal methods, highly cited foundational study\",\n      \"pmids\": [\"18268103\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"The Pih1-Tah1 heterodimer (yeast orthologs) binds Hsp90 with similar affinity and stoichiometry as Tah1 alone but inhibits Hsp90 ATPase activity; Pih1 alone is unstable and degraded from its N terminus, while the Pih1-Tah1 complex is stable. The region within Pih1 responsible for Tah1 interaction and Hsp90 ATPase inhibition was identified.\",\n      \"method\": \"Analytical ultracentrifugation, microcalorimetry (ITC), noncovalent mass spectrometry, ATPase assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — multiple rigorous biophysical methods, in vitro enzymatic assay, mutagenesis-guided domain mapping\",\n      \"pmids\": [\"20663878\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Tah1 (yeast ortholog of RPAP3) binds the C terminus of Pih1 through its C-helix and unstructured region; the C terminus of Pih1 destabilizes the protein in vitro and in vivo, whereas Tah1 binding forms a stable complex. NMR structure of Tah1 reveals two TPR motifs plus a C-helix binding the Hsp90 EEVD C-terminal motif via a two-carboxylate clamp.\",\n      \"method\": \"NMR structure determination, co-immunoprecipitation, in vitro binding assays, in vivo stability assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — NMR structure with functional validation of binding and stability, multiple orthogonal methods\",\n      \"pmids\": [\"22179618\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"The C terminus of Pih1 (yeast ortholog) contains multiple degron/destabilization elements including two intrinsically disordered regions; IDR2 mediates Tah1 binding. Pih1 N-terminal domain (residues 1–195/1–230) binds Rvb1/Rvb2 heterocomplex, and the sequence between the two disordered regions enhances this binding. Pih1(1–230) complements full-length Pih1 function at 37°C.\",\n      \"method\": \"Site-directed mutagenesis, in vitro and in vivo stability assays, co-immunoprecipitation, yeast complementation\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — mutagenesis combined with in vivo and in vitro binding assays, multiple orthogonal methods\",\n      \"pmids\": [\"23139418\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"PIH1D1 contains a phosphopeptide-binding domain (PIH-N) that preferentially binds highly acidic phosphorylated proteins. A co-crystal structure of PIH-N with a TEL2 phosphopeptide reveals that Lys57 and Lys64 in PIH1D1, together with a conserved DpSDD motif in TEL2, are essential for binding. Proteomic analysis identified multiple R2TP substrates recruited via this phosphorylation-dependent mechanism (CK2 phosphorylation-dependent recognition).\",\n      \"method\": \"X-ray crystallography (co-crystal structure), site-directed mutagenesis, proteomic/MS interactome analysis, in vitro binding assays\",\n      \"journal\": \"Cell reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — crystal structure plus mutagenesis plus proteomic validation, two independent papers confirm same mechanism\",\n      \"pmids\": [\"24656813\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"PIH1D1 contains a domain specific for binding CK2 phosphorylation sites, mediating recruitment of TEL2 (and the TTT complex) to the Hsp90/R2TP system; structural and biochemical analysis defined Hsp90-Tah1-Pih1, Hsp90-Spagh (RPAP3), and PIH1D1-TEL2 complex architectures.\",\n      \"method\": \"X-ray crystallography (multiple complex structures), biochemical binding assays, isothermal titration calorimetry\",\n      \"journal\": \"Structure\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — crystal structures of multiple complexes with functional biochemical validation, confirms findings of PMID:24656813\",\n      \"pmids\": [\"24794838\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Human PIH1D1 specifically co-immunoprecipitates Raptor (mTORC1-specific) but not Rictor (mTORC2-specific); knockdown of PIH1D1 decreases mTORC1 assembly, S6 kinase phosphorylation, and rRNA transcription without affecting mTORC2.\",\n      \"method\": \"Co-immunoprecipitation, siRNA knockdown, S6K phosphorylation assay, rRNA transcription assay\",\n      \"journal\": \"FEBS letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — Co-IP plus functional KD phenotype, but single lab with moderate methods\",\n      \"pmids\": [\"24036451\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Human PIH1 (PIH1D1) directly interacts with histone H4 and recruits the Brg1-SWI/SNF complex (via SNF5) to rRNA gene promoters, mediates DNase I-hypersensitive chromatin remodeling at the core promoter, promotes RNA Pol I occupancy and rRNA transcription initiation, and displaces TIP5 (a NoRC silencing component) from the core region.\",\n      \"method\": \"Co-immunoprecipitation, ChIP assays, DNase I hypersensitivity assay, siRNA knockdown, in vitro binding\",\n      \"journal\": \"Journal of molecular cell biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — multiple ChIP and functional assays, single lab\",\n      \"pmids\": [\"22368283\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"PIH1D1 interacts with SNF5 (a core subunit of the SWI/SNF chromatin remodeling complex) and stabilizes SNF5 by attenuating its proteasome-mediated degradation.\",\n      \"method\": \"Co-immunoprecipitation, cycloheximide chase, proteasome inhibitor (MG132) treatment, plasmid overexpression\",\n      \"journal\": \"Acta Academiae Medicinae Sinicae\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — single lab, single method set, limited mechanistic depth\",\n      \"pmids\": [\"20078948\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"PIH1D1 interacts with both RPAP3 and Monad (Reptin/RUVBL2) in human cells; siRNA-mediated knockdown of PIH1D1 enhances doxorubicin-induced apoptosis and caspase-3 activation, placing PIH1D1 as a modulator of the apoptosis pathway.\",\n      \"method\": \"Co-immunoprecipitation, siRNA knockdown, caspase-3 activation assay\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — single Co-IP and KD phenotype, no pathway placement beyond apoptosis modulation\",\n      \"pmids\": [\"21078300\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"RPAP3 isoform 1 (but not isoform 2) interacts with PIH1D1 to form the R2TP complex; knockdown of RPAP3 isoform 1 downregulates PIH1D1 protein level without affecting PIH1D1 mRNA, indicating post-transcriptional stabilization of PIH1D1 by RPAP3 isoform 1.\",\n      \"method\": \"Co-immunoprecipitation, siRNA knockdown, RT-PCR, Western blot\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 + Moderate — co-IP plus mRNA/protein level dissection provides mechanistic insight into complex composition and PIH1D1 stability\",\n      \"pmids\": [\"23159623\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Yeast Pih1 (PIH1D1 ortholog) directly interacts with snoRNP assembly factor Rsa1p (NUFIP1) and snoRNP core protein Nop58p; these two interactions are mutually exclusive. NMR and ITC mapping identified the binding domains. Tah1p (RPAP3) can stabilize Pih1p in the absence of Hsp82 (Hsp90) activity during stationary phase, via direct contacts between the Pih1p CS domain and Tah1p C-terminal tail forming two intermolecular β-sheets.\",\n      \"method\": \"NMR structure, ITC, co-expression in E. coli, in vivo and in vitro binding assays\",\n      \"journal\": \"Journal of molecular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — NMR solution structure plus ITC plus co-expression reconstitution, multiple orthogonal methods\",\n      \"pmids\": [\"26210662\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"Yeast Pih1 (PIH1D1 ortholog) undergoes ubiquitin-independent proteasomal degradation mediated by direct interaction between the Pih1 C-terminal fragment and the C-terminal 30 amino acids of proteasome subunit Rpn8; this interaction is specifically revealed when Hsp90 co-chaperone Tah1 is depleted.\",\n      \"method\": \"Co-immunoprecipitation, truncation mutagenesis, in vitro and in vivo degradation assays, GFP-fusion reporter degradation assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — in vitro and in vivo degradation assays with mutagenesis, identifying specific proteasome subunit mediating ubiquitin-independent degradation\",\n      \"pmids\": [\"27053109\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Yeast Nop17/Pih1 (PIH1D1 ortholog) interacts with Nop58 in an ATP-dependent manner with respect to Rvb1/2; the R2TP complex reduces Nop58 affinity for snoRNA, facilitating binding of other snoRNP subunits during box C/D snoRNP assembly.\",\n      \"method\": \"In vitro binding assays, domain mapping, ATP dependency experiments\",\n      \"journal\": \"BMC molecular biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — in vitro binding with domain mapping, single lab, moderate mechanistic resolution\",\n      \"pmids\": [\"25888478\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"In Trypanosoma brucei, PIH1D1 (a DNAAF PIH-family protein) concentrates at co-translational assembly sites on translating outer dynein arm heavy chains (HCs); loss of PIH1D1 reduces HC protein levels and leaves the IC-LC complex stranded in the cytoplasm, indicating PIH1D1 generates specialized compartments for co-translational folding of HCs and their assembly with other ODA subunits.\",\n      \"method\": \"Live imaging, genetic knockout, immunofluorescence, ribosome profiling/co-translational assembly assays in T. brucei\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 — preprint, single organism model distant from mammalian system, no peer review\",\n      \"pmids\": [\"bio_10.1101_2025.07.26.666928\"],\n      \"is_preprint\": true\n    }\n  ],\n  \"current_model\": \"PIH1D1 is the substrate-recognition subunit of the R2TP co-chaperone complex (with RPAP3/Tah1, RUVBL1/Rvb1, and RUVBL2/Rvb2) that bridges client proteins to Hsp90: its N-terminal PIH-N domain binds CK2-phosphorylated DpSDD motifs on substrates such as TEL2 (defined by co-crystal structure and mutagenesis), its C-terminal CS domain interacts with RPAP3 to form a stable heterodimer that inhibits Hsp90 ATPase activity, and together the complex directs assembly of box C/D and H/ACA snoRNPs, mTORC1, RNA Pol II, and PIKK complexes; when not protected by RPAP3/Hsp90, PIH1D1 is degraded via ubiquitin-independent proteasomal degradation mediated by direct binding to proteasome subunit Rpn8.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"PIH1D1 is the substrate-recognition subunit of the R2TP co-chaperone complex (with RPAP3/Tah1, RUVBL1, and RUVBL2) that couples Hsp90 chaperone activity to the assembly of macromolecular complexes including box C/D and H/ACA snoRNPs, mTORC1, and PIKK signaling complexes [PMID:18268103, PMID:24036451]. Its N-terminal PIH-N domain recognizes CK2-phosphorylated DpSDD motifs on substrates such as TEL2, as defined by co-crystal structures and mutagenesis of key residues Lys57 and Lys64, while its C-terminal CS domain heterodimerizes with RPAP3 and inhibits Hsp90 ATPase activity [PMID:24656813, PMID:24794838, PMID:20663878]. PIH1D1 is intrinsically unstable: RPAP3 binding stabilizes the protein post-translationally, and in the absence of this protection PIH1D1 undergoes ubiquitin-independent proteasomal degradation mediated by direct interaction of its C-terminal region with proteasome subunit Rpn8 [PMID:23159623, PMID:27053109]. PIH1D1 also participates in rRNA gene transcription by recruiting the Brg1–SWI/SNF chromatin remodeling complex to rDNA promoters, promoting RNA Pol I occupancy and displacing the silencing factor TIP5 [PMID:22368283].\",\n  \"teleology\": [\n    {\n      \"year\": 2008,\n      \"claim\": \"Identification of Pih1 as a core subunit of the R2TP complex established that an Hsp90-associated co-chaperone machinery is required for snoRNP biogenesis, answering why box C/D and H/ACA snoRNP accumulation depends on Hsp90.\",\n      \"evidence\": \"Genetic interaction screens, reciprocal Co-IP, and snoRNA accumulation assays in S. cerevisiae\",\n      \"pmids\": [\"18268103\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism by which R2TP remodels snoRNP precursors was unknown\", \"Human complex composition unverified at this stage\", \"Substrate recognition mode of Pih1 undefined\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Biophysical characterization of the Pih1–Tah1 heterodimer revealed that Pih1 is inherently unstable and that the heterodimer inhibits Hsp90 ATPase activity, establishing that R2TP modulates the chaperone cycle rather than passively recruiting Hsp90.\",\n      \"evidence\": \"Analytical ultracentrifugation, ITC, noncovalent mass spectrometry, and ATPase assays with purified yeast proteins\",\n      \"pmids\": [\"20663878\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of Pih1–Tah1 interaction not yet resolved\", \"Functional consequence of ATPase inhibition on substrate assembly unclear\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"NMR structure of Tah1 and mapping of its Pih1-binding interface showed that Tah1 engages Pih1's destabilizing C-terminus to form a stable complex, explaining how R2TP integrity is maintained.\",\n      \"evidence\": \"NMR structure determination with binding and stability assays in yeast\",\n      \"pmids\": [\"22179618\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Full-length Pih1 structure unavailable\", \"Role of intrinsically disordered regions in Pih1 function unresolved\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Domain dissection of Pih1 identified that its N-terminal domain binds Rvb1/Rvb2 while disordered C-terminal elements contain degron and Tah1-binding functions, defining the modular architecture that separates substrate engagement from complex stabilization.\",\n      \"evidence\": \"Site-directed mutagenesis, Co-IP, and yeast complementation assays\",\n      \"pmids\": [\"23139418\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Identity of substrates recognized by the N-terminal domain not determined\", \"Phosphorylation-dependent recognition not yet discovered\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Demonstration that PIH1D1 binds histone H4, recruits Brg1–SWI/SNF to rDNA promoters, and promotes RNA Pol I occupancy expanded PIH1D1 function beyond snoRNP assembly to transcriptional regulation of rRNA genes.\",\n      \"evidence\": \"ChIP, DNase I hypersensitivity, Co-IP, and siRNA knockdown in human cells\",\n      \"pmids\": [\"22368283\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether this chromatin-remodeling role is R2TP-dependent or independent was not tested\", \"Relevance to non-rDNA loci unknown\", \"Single lab finding not independently confirmed\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Showing that RPAP3 isoform 1 specifically stabilizes PIH1D1 at the post-transcriptional level confirmed the Pih1 stability paradigm in human cells and identified isoform specificity within the R2TP complex.\",\n      \"evidence\": \"Co-IP, siRNA knockdown with RT-PCR and Western blot in human cells\",\n      \"pmids\": [\"23159623\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism of post-transcriptional stabilization (folding vs. degradation shielding) not resolved\", \"Isoform 2 function unexplored\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Co-IP of PIH1D1 with Raptor but not Rictor, and reduced mTORC1 assembly upon PIH1D1 knockdown, established that R2TP specifically promotes mTORC1 but not mTORC2 assembly, broadening the client repertoire beyond snoRNPs.\",\n      \"evidence\": \"Co-IP, siRNA knockdown, S6K phosphorylation assay in human cells\",\n      \"pmids\": [\"24036451\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct versus indirect nature of PIH1D1–Raptor interaction not resolved\", \"Whether TEL2/TTT mediates this interaction was not tested at this stage\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Co-crystal structures of the PIH-N domain with a TEL2 phosphopeptide, together with proteomic identification of CK2-phosphorylated substrates, established the molecular basis of phospho-dependent substrate recognition — the central mechanistic step of how R2TP selects its clients.\",\n      \"evidence\": \"X-ray crystallography, site-directed mutagenesis, ITC, and proteomic/MS analysis\",\n      \"pmids\": [\"24656813\", \"24794838\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural view of the full R2TP complex with a client protein not available\", \"Not all proteomic hits validated as bona fide assembly substrates\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"NMR and ITC studies showing mutually exclusive binding of Pih1 to Rsa1 (NUFIP1) and Nop58 revealed a hand-off mechanism in snoRNP assembly, and showed that Tah1 can stabilize Pih1 independently of Hsp90 activity.\",\n      \"evidence\": \"NMR structure, ITC, and co-expression reconstitution in yeast/E. coli\",\n      \"pmids\": [\"26210662\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether the hand-off mechanism is conserved in human cells not tested\", \"Kinetics of the hand-off in vivo not measured\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"ATP-dependent interaction of Pih1 with Nop58 via Rvb1/2 and reduced Nop58–snoRNA affinity by R2TP clarified how the complex actively remodels RNP intermediates rather than acting as a passive scaffold.\",\n      \"evidence\": \"In vitro binding assays with ATP dependency experiments in yeast\",\n      \"pmids\": [\"25888478\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Precise stoichiometry of the remodeling intermediate unknown\", \"Whether Rvb1/2 ATPase activity is the driving force not directly demonstrated\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Discovery that Pih1 undergoes ubiquitin-independent proteasomal degradation via direct binding to proteasome subunit Rpn8 explained the mechanistic basis of Pih1 instability and how R2TP disassembly leads to rapid PIH1D1 turnover.\",\n      \"evidence\": \"Co-IP, truncation mutagenesis, and in vitro/in vivo degradation assays in yeast\",\n      \"pmids\": [\"27053109\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether this ubiquitin-independent degradation pathway operates in mammalian cells not established\", \"Structural basis of the Pih1–Rpn8 interaction not resolved\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"A full structural view of the human R2TP complex engaged with a client during active assembly, and the relative contributions of PIH1D1's rDNA chromatin-remodeling function versus its canonical R2TP role, remain unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No cryo-EM or crystal structure of a complete human R2TP–client assembly\", \"Relative in vivo importance of R2TP-independent functions (rDNA regulation, apoptosis modulation) not determined\", \"Full catalog of bona fide PIH1D1-dependent assembly clients in human cells is incomplete\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [0, 4, 5, 6]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [1, 11]},\n      {\"term_id\": \"GO:0042393\", \"supporting_discovery_ids\": [7]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005730\", \"supporting_discovery_ids\": [7]},\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [7, 8]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-8953854\", \"supporting_discovery_ids\": [0, 11, 13]},\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [4, 5, 12]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [6]},\n      {\"term_id\": \"R-HSA-74160\", \"supporting_discovery_ids\": [7]}\n    ],\n    \"complexes\": [\n      \"R2TP\"\n    ],\n    \"partners\": [\n      \"RPAP3\",\n      \"RUVBL1\",\n      \"RUVBL2\",\n      \"TEL2\",\n      \"NOP58\",\n      \"NUFIP1\",\n      \"SMARCB1\",\n      \"RPTOR\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}