{"gene":"PAIP2","run_date":"2026-06-10T05:19:53","timeline":{"discoveries":[{"year":2001,"finding":"Paip2 is a novel PABP-interacting protein that represses translation both in vitro and in vivo by decreasing the affinity of PABP for polyadenylate RNA and disrupting the repeating structure of poly(A) RNP; it preferentially inhibits translation of poly(A)-containing mRNA but not cap- and eIF4G-independent HCV IRES-mediated translation. Paip2 also competes with Paip1 for PABP binding.","method":"In vitro translation assay, in vivo transfection, PABP-poly(A) binding assays, competition binding","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 1-2 / Strong — multiple orthogonal methods (in vitro translation, in vivo assays, binding assays) in a single rigorous study establishing mechanism","pmids":["11172725"],"is_preprint":false},{"year":2001,"finding":"Paip2 contains two binding sites for PABP: a 16-amino-acid C-terminal stretch and a central region. PABP also has two binding regions for Paip2: the RRM region and the C-terminal region. The stoichiometry is 2:1 (Paip2:PABP), with two independent Kd values of 0.66 nM and 74 nM. Only the central Paip2 fragment (binding PABP RRM with high affinity) inhibits PABP-poly(A) binding and translation.","method":"Biacore surface plasmon resonance, far-Western analysis, deletion mapping","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 1 / Strong — quantitative biophysical measurements (Biacore) combined with far-Western analysis, multiple orthogonal methods defining stoichiometry and binding domains","pmids":["11438674"],"is_preprint":false},{"year":2006,"finding":"Paip2 protein stability is regulated by the E3 ubiquitin ligase EDD: upon PABP depletion, Paip2 interacts with EDD, which ubiquitinates Paip2 and targets it for proteasomal degradation. Knockdown of EDD increases Paip2 stability. This establishes a homeostatic feedback loop whereby PABP levels regulate Paip2 turnover.","method":"RNAi knockdown of PABP and EDD, co-immunoprecipitation, ubiquitination assay, protein stability measurements","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 2 / Moderate — reciprocal Co-IP, siRNA knockdown experiments with multiple readouts (ubiquitination assay, protein stability) in a single lab","pmids":["16601676"],"is_preprint":false},{"year":2006,"finding":"Paip2 inhibits translation by a second mechanism: competing with eIF4G for binding to PABP, independent of its ability to disrupt PABP-poly(A) interaction. This was demonstrated by showing Paip2 inhibits translation when PABP is tethered to the 3' end of mRNA (bypassing poly(A) displacement).","method":"In vitro translation assay with tethered PABP, competition binding assay","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1-2 / Moderate — in vitro reconstitution with tethered PABP system and competition binding, demonstrating a distinct second mechanism in a single focused study","pmids":["16772376"],"is_preprint":false},{"year":2006,"finding":"Paip2B (a homolog of Paip2A sharing 59% identity) inhibits translation of capped and polyadenylated mRNAs both in vitro and in vivo by displacing PABP from the poly(A) tail, similar to Paip2A. However, Paip2A is more highly ubiquitinated than Paip2B and is degraded more rapidly by the proteasome.","method":"In vitro translation assay, in vivo overexpression, ubiquitination assay, proteasome inhibitor treatment","journal":"RNA (New York, N.Y.)","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple functional assays (in vitro translation, in vivo, ubiquitination) from a single lab comparing the two paralogs","pmids":["16804161"],"is_preprint":false},{"year":2010,"finding":"Paip2a knockout mice are male-infertile; Paip2a/Paip2b double-KO mice show inhibited translation of mRNAs encoding proteins essential for spermiogenesis in late spermatids. This is caused by aberrant PABP overexpression (due to loss of Paip2-mediated homeostasis), which impairs eIF4E interaction with the 5' cap structure.","method":"Knockout mouse generation, polysome profiling, Western blot, co-immunoprecipitation (eIF4E-cap interaction assay)","journal":"The Journal of clinical investigation","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic KO with specific molecular phenotype (impaired eIF4E-cap interaction), replicated across single and double KO, multiple orthogonal methods","pmids":["20739757"],"is_preprint":false},{"year":2013,"finding":"Poly(A) RNA induces a conformational change in PABP in which RRM1 comes into proximity with RRM4, bending the region between RRM2 and RRM3. Paip2 disrupts this bent structure, converting PABP to an extended conformation and thereby inhibiting PABP-poly(A) binding.","method":"Single-molecule real-time visualization (FRET/single-molecule imaging) of individual PABP molecules","journal":"Nucleic acids research","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — single-molecule imaging approach demonstrating conformational change, single lab, single method","pmids":["24293655"],"is_preprint":false},{"year":2013,"finding":"During HCMV infection, Paip2 accumulates alongside PABP1 and EDD1 (via the viral UL38 mTORC1 activator), increases its association with PABP1, and acts as an innate restriction factor limiting viral protein synthesis. Depleting Paip2 restored eIF4F assembly and promoted viral replication without increasing PABP1.","method":"siRNA depletion of Paip2, co-immunoprecipitation, Western blot, viral replication assay, eIF4F assembly assay","journal":"Genes & development","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal methods (siRNA depletion, Co-IP, viral replication assay) in a single lab establishing a new functional role","pmids":["23964095"],"is_preprint":false},{"year":2019,"finding":"PAIP2 prevents translation termination at premature termination codons by inhibiting PABP activity at its C-terminal domain. PAIP2 inhibits free PABP-stimulated translation termination in vitro; however, once PABP is bound to the poly(A) tail, it becomes insensitive to PAIP2 suppression and efficiently activates translation termination via eRF3a.","method":"In vitro translation termination reconstitution assay, biochemical competition experiments with purified components","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro reconstitution assay with purified components, clear positive and negative conditions tested, single lab","pmids":["30992367"],"is_preprint":false},{"year":2019,"finding":"In Drosophila, nuclear Paip2 is part of an ~300-kDa protein complex and interacts with the mRNA capping factor (Cbp80) and factors of RNA Pol II transcription initiation and early elongation. Paip2 functionally cooperates with Cbp80 to ensure proper Pol II CTD Ser5 phosphorylation at the promoter.","method":"Co-immunoprecipitation, mass spectrometry, ChIP, Pol II CTD phosphorylation assay (Drosophila)","journal":"FEBS letters","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP with mass spectrometry plus functional CTD phosphorylation assay, single lab, Drosophila ortholog","pmids":["31001806"],"is_preprint":false},{"year":2018,"finding":"In Drosophila, Paip2 is present in the nucleus and associates with chromatin at promoter regions of active genes via an RNA-dependent (indirect) interaction, suggesting Paip2 is recruited to mRNAs co-transcriptionally.","method":"Chromatin immunoprecipitation (ChIP), nuclear fractionation, RNase treatment, immunofluorescence in Drosophila tissues","journal":"Cell cycle (Georgetown, Tex.)","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — ChIP and fractionation with RNase sensitivity controls, single lab, Drosophila ortholog","pmids":["29995569"],"is_preprint":false},{"year":2022,"finding":"Paip2A competitively binds the RRM2-RRM3 region of PABPC1 with Kd ~1 nM (comparable to poly(A) affinity). Mechanistically, Paip2A first binds RRM2 of poly(A)-bound PABPC1, and RRM2-anchored Paip2A then displaces RRM3 from poly(A), causing full dissociation of PABPC1 from the poly(A) tail.","method":"Isothermal titration calorimetry (ITC), NMR spectroscopy with structural analysis of RRM-ligand interactions","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — quantitative ITC plus NMR structural characterization, two orthogonal biophysical methods, mechanistic model validated in a single rigorous study","pmids":["35307347"],"is_preprint":false},{"year":2015,"finding":"ROCK inhibitor treatment increases PAIP2 expression via transcriptional upregulation by HNF4A, facilitated by increased ROCK1 nuclear localization and ROCK1 association with HNF4A. Elevated PAIP2 enhances poly(A) shortening of miRNA-targeted mRNAs, globally upregulating miRNA function.","method":"ROCK inhibitor treatment, siRNA knockdown of PAIP2 and ROCK1, reporter assays for miRNA function, co-immunoprecipitation (ROCK1-HNF4A), nuclear fractionation","journal":"Nucleic acids research","confidence":"Medium","confidence_rationale":"Tier 2-3 / Moderate — multiple experiments (Co-IP, nuclear fractionation, functional miRNA assays) from a single lab, but mechanism is indirect","pmids":["26187994"],"is_preprint":false},{"year":2011,"finding":"Paip2 overexpression suppresses Ras(V12)-induced cellular transformation (colony formation in semi-solid matrix and focus formation), and this activity requires Paip2's ability to bind PABP.","method":"Soft-agar colony formation assay, focus formation assay, PABP-binding mutant of Paip2","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2-3 / Weak — functional transformation assays with mutant analysis, single lab, single study","pmids":["21957478"],"is_preprint":false},{"year":2024,"finding":"In Drosophila, Paip2 directly binds ENY2 in vitro and interacts with the ENY2-containing TREX-2 complex in vivo. Paip2 is present at the histone gene locus and histone locus bodies (HLBs). Paip2 knockdown decreases TREX-2 subunit association with histone mRNP particles, suggesting Paip2 facilitates TREX-2 binding to histone mRNPs.","method":"Yeast two-hybrid, in vitro pull-down, co-immunoprecipitation, ChIP, RNA interference knockdown, RNP particle fractionation (Drosophila)","journal":"Molekuliarnaia biologiia","confidence":"Medium","confidence_rationale":"Tier 2-3 / Moderate — multiple methods (yeast two-hybrid, in vitro binding, Co-IP, RNAi knockdown) supporting a new nuclear function in Drosophila ortholog","pmids":["39707855"],"is_preprint":false}],"current_model":"PAIP2 (Paip2A) is a translational repressor that binds PABPC1 at two sites (primarily RRM2-RRM3) with ~1 nM affinity, competitively displacing PABP from the poly(A) tail by a sequential RRM2-anchoring/RRM3-displacement mechanism and also competing with eIF4G for PABP binding; PAIP2 protein stability is homeostatically regulated by the E3 ubiquitin ligase EDD in a PABP-dependent manner, its nuclear form participates in co-transcriptional mRNA processing and Pol II CTD Ser5 phosphorylation in Drosophila, and it is required for proper translational activation during late spermiogenesis in mice."},"narrative":{"mechanistic_narrative":"PAIP2 (Paip2A) is a translational repressor that controls cytoplasmic translation by antagonizing poly(A)-binding protein (PABP/PABPC1) [PMID:11172725]. It binds PABP at two sites via two contact regions on PABP and decreases PABP affinity for polyadenylate RNA, disrupting poly(A) RNP structure and selectively inhibiting translation of poly(A)-containing mRNAs while sparing cap- and eIF4G-independent IRES translation [PMID:11172725, PMID:11438674]. PAIP2 engages the RRM2–RRM3 region of PABPC1 with ~1 nM affinity and displaces it from poly(A) through a sequential mechanism in which RRM2-anchored PAIP2 dislodges RRM3 from the poly(A) tail [PMID:35307347], reversing the bent, poly(A)-induced PABP conformation into an extended state [PMID:24293655]. PAIP2 represses translation by a second, independent route: competing with eIF4G for PABP binding even when PABP is tethered to mRNA [PMID:16772376], and it also blocks free PABP from stimulating eRF3a-dependent translation termination [PMID:30992367]. PAIP2 abundance is set by a homeostatic feedback loop in which the E3 ubiquitin ligase EDD ubiquitinates PAIP2 for proteasomal degradation upon PABP depletion, coupling PAIP2 stability to PABP levels [PMID:16601676]. Genetically, Paip2a/Paip2b loss in mice causes male infertility through aberrant PABP overexpression that impairs eIF4E–cap interaction and blocks the translational activation required for late spermiogenesis [PMID:20739757]. Beyond its cytoplasmic role, a nuclear pool of the Drosophila ortholog associates co-transcriptionally with chromatin at active promoters and cooperates with capping and TREX-2 factors in mRNA processing [PMID:31001806, PMID:29995569, PMID:39707855].","teleology":[{"year":2001,"claim":"Established that PAIP2 is a dedicated PABP-interacting translational repressor that works by lowering PABP affinity for the poly(A) tail, defining the gene's core biological role.","evidence":"In vitro translation assays, in vivo transfection, PABP–poly(A) binding and competition assays","pmids":["11172725"],"confidence":"High","gaps":["Did not define the structural basis or affinity of the PAIP2–PABP interaction","Did not address how PAIP2 levels are regulated in cells"]},{"year":2001,"claim":"Quantified the bivalent PAIP2–PABP architecture, showing two binding sites on each partner with 2:1 stoichiometry and identifying the central PABP-RRM-binding fragment as the active repressive module.","evidence":"Biacore surface plasmon resonance, far-Western, deletion mapping","pmids":["11438674"],"confidence":"High","gaps":["Did not resolve the atomic-level RRM contacts","Did not establish which interaction operates in vivo"]},{"year":2006,"claim":"Revealed that PAIP2 abundance is homeostatically coupled to PABP via EDD-mediated ubiquitination and proteasomal degradation, explaining how repressor and target levels are balanced.","evidence":"RNAi knockdown of PABP and EDD, reciprocal Co-IP, ubiquitination and protein-stability assays","pmids":["16601676"],"confidence":"High","gaps":["Did not identify the ubiquitinated residues on PAIP2","Did not establish how PABP binding shields PAIP2 from EDD"]},{"year":2006,"claim":"Demonstrated a second, poly(A)-displacement-independent repression mechanism whereby PAIP2 competes with eIF4G for PABP, broadening the model beyond simple poly(A) release.","evidence":"In vitro translation with tethered PABP, competition binding","pmids":["16772376"],"confidence":"High","gaps":["Did not quantify the relative contribution of each mechanism in vivo"]},{"year":2006,"claim":"Showed the paralog Paip2B represses translation by the same poly(A)-displacement mechanism but is more stable than the more heavily ubiquitinated Paip2A, distinguishing the two family members.","evidence":"In vitro/in vivo translation assays, ubiquitination assay, proteasome inhibition","pmids":["16804161"],"confidence":"Medium","gaps":["Single-lab paralog comparison","Did not establish distinct physiological roles for Paip2A vs Paip2B"]},{"year":2010,"claim":"Provided in vivo genetic proof that PAIP2-mediated PABP homeostasis is essential, as its loss causes male infertility through PABP overexpression that impairs eIF4E–cap binding during spermiogenesis.","evidence":"Single and double knockout mice, polysome profiling, eIF4E–cap interaction Co-IP","pmids":["20739757"],"confidence":"High","gaps":["Did not define which spermatid mRNAs are directly affected","Did not test roles in non-germline tissues"]},{"year":2011,"claim":"Linked PAIP2's PABP-binding activity to tumor-suppressive function by showing it suppresses Ras-induced transformation in a PABP-binding-dependent manner.","evidence":"Soft-agar colony and focus formation assays with a PABP-binding mutant","pmids":["21957478"],"confidence":"Medium","gaps":["Single study with cell-based transformation readouts only","No in vivo tumor evidence","Downstream mRNA targets not identified"]},{"year":2013,"claim":"Provided a structural rationale for repression by showing poly(A) bends PABP and that PAIP2 disrupts this bent conformation to inhibit poly(A) binding.","evidence":"Single-molecule real-time imaging of individual PABP molecules","pmids":["24293655"],"confidence":"Medium","gaps":["Single method, single lab","Did not map the conformational change to specific RRM contacts"]},{"year":2013,"claim":"Assigned PAIP2 an antiviral role as an innate restriction factor that limits eIF4F assembly and viral protein synthesis during HCMV infection.","evidence":"siRNA depletion, Co-IP, viral replication and eIF4F assembly assays","pmids":["23964095"],"confidence":"Medium","gaps":["Limited to HCMV context","Did not establish breadth across other viruses"]},{"year":2015,"claim":"Connected PAIP2 to miRNA function, showing transcriptional upregulation of PAIP2 via HNF4A enhances poly(A) shortening of miRNA-targeted mRNAs.","evidence":"ROCK inhibitor treatment, siRNA knockdown, miRNA reporter assays, Co-IP, nuclear fractionation","pmids":["26187994"],"confidence":"Medium","gaps":["Mechanistic link is indirect","Did not define how PAIP2 promotes deadenylation mechanistically"]},{"year":2018,"claim":"Identified a nuclear, chromatin-associated pool of Paip2 recruited co-transcriptionally to active promoters via RNA-dependent interaction, extending PAIP2 beyond cytoplasmic translation.","evidence":"ChIP, nuclear fractionation, RNase treatment, immunofluorescence (Drosophila)","pmids":["29995569"],"confidence":"Medium","gaps":["Drosophila ortholog only","Direct chromatin/RNA-binding partners not defined"]},{"year":2019,"claim":"Refined the termination model, showing PAIP2 blocks free PABP from stimulating eRF3a-dependent termination but loses this control once PABP is poly(A)-bound.","evidence":"In vitro translation termination reconstitution with purified components","pmids":["30992367"],"confidence":"High","gaps":["Cellular relevance of premature termination control not established"]},{"year":2019,"claim":"Defined a nuclear Paip2 complex linking it to mRNA capping and Pol II transcription, showing cooperation with Cbp80 for proper CTD Ser5 phosphorylation.","evidence":"Co-IP, mass spectrometry, ChIP, CTD phosphorylation assay (Drosophila)","pmids":["31001806"],"confidence":"Medium","gaps":["Drosophila ortholog only","Whether human PAIP2 has an equivalent nuclear role is untested"]},{"year":2022,"claim":"Resolved the molecular mechanism of poly(A) displacement, showing PAIP2A binds RRM2 first then displaces RRM3 from poly(A) with ~1 nM affinity comparable to poly(A) itself.","evidence":"Isothermal titration calorimetry and NMR structural analysis","pmids":["35307347"],"confidence":"High","gaps":["Did not capture a full-length complex structure","Did not integrate eIF4G-competition mechanism structurally"]},{"year":2024,"claim":"Extended the nuclear function by showing Paip2 binds ENY2 and the TREX-2 complex and facilitates TREX-2 association with histone mRNPs at histone locus bodies.","evidence":"Yeast two-hybrid, in vitro pull-down, Co-IP, ChIP, RNAi, RNP fractionation (Drosophila)","pmids":["39707855"],"confidence":"Medium","gaps":["Drosophila ortholog only","Functional consequence for histone mRNA processing not quantified"]},{"year":null,"claim":"Whether the nuclear, co-transcriptional and TREX-2/histone-locus functions documented for the Drosophila ortholog are conserved in mammalian PAIP2 remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No direct evidence for human PAIP2 nuclear chromatin function","Relationship between cytoplasmic repressor and nuclear roles undefined"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[0,1,3,8,11]},{"term_id":"GO:0045182","term_label":"translation regulator activity","supporting_discovery_ids":[0,3,8]},{"term_id":"GO:0140313","term_label":"molecular sequestering activity","supporting_discovery_ids":[0,11]}],"localization":[{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[0,5]},{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[9,10]}],"pathway":[{"term_id":"R-HSA-8953854","term_label":"Metabolism of RNA","supporting_discovery_ids":[0,8,12]},{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[2]}],"complexes":["TREX-2"],"partners":["PABPC1","EDD/UBR5","EIF4G","PAIP1","ENY2","CBP80"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q9BPZ3","full_name":"Polyadenylate-binding protein-interacting protein 2","aliases":[],"length_aa":127,"mass_kda":15.0,"function":"Acts as a repressor in the regulation of translation initiation of poly(A)-containing mRNAs. Its inhibitory activity on translation is mediated via its action on PABPC1. Displaces the interaction of PABPC1 with poly(A) RNA and competes with PAIP1 for binding to PABPC1. Its association with PABPC1 results in disruption of the cytoplasmic poly(A) RNP structure organization","subcellular_location":"Cytoplasm","url":"https://www.uniprot.org/uniprotkb/Q9BPZ3/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/PAIP2","classification":"Not Classified","n_dependent_lines":9,"n_total_lines":1208,"dependency_fraction":0.0074503311258278145},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/PAIP2","total_profiled":1310},"omim":[{"mim_id":"611018","title":"POLYADENYLATE-BINDING PROTEIN-INTERACTING PROTEIN 2B; PAIP2B","url":"https://www.omim.org/entry/611018"},{"mim_id":"605604","title":"POLYADENYLATE-BINDING PROTEIN-INTERACTING PROTEIN 2; PAIP2","url":"https://www.omim.org/entry/605604"},{"mim_id":"192240","title":"VASCULAR ENDOTHELIAL GROWTH FACTOR A; VEGFA","url":"https://www.omim.org/entry/192240"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Vesicles","reliability":"Supported"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/PAIP2"},"hgnc":{"alias_symbol":["PAIP2A"],"prev_symbol":[]},"alphafold":{"accession":"Q9BPZ3","domains":[{"cath_id":"1.20.5","chopping":"26-76","consensus_level":"medium","plddt":85.7602,"start":26,"end":76}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9BPZ3","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q9BPZ3-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q9BPZ3-F1-predicted_aligned_error_v6.png","plddt_mean":70.81},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=PAIP2","jax_strain_url":"https://www.jax.org/strain/search?query=PAIP2"},"sequence":{"accession":"Q9BPZ3","fasta_url":"https://rest.uniprot.org/uniprotkb/Q9BPZ3.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q9BPZ3/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9BPZ3"}},"corpus_meta":[{"pmid":"11172725","id":"PMC_11172725","title":"Translational repression by a novel partner of human poly(A) binding protein, Paip2.","date":"2001","source":"Molecular cell","url":"https://pubmed.ncbi.nlm.nih.gov/11172725","citation_count":183,"is_preprint":false},{"pmid":"11438674","id":"PMC_11438674","title":"Dual interactions of the translational repressor Paip2 with poly(A) binding protein.","date":"2001","source":"Molecular and cellular biology","url":"https://pubmed.ncbi.nlm.nih.gov/11438674","citation_count":134,"is_preprint":false},{"pmid":"16601676","id":"PMC_16601676","title":"Poly(A) binding protein (PABP) homeostasis is mediated by the stability of its inhibitor, Paip2.","date":"2006","source":"The EMBO journal","url":"https://pubmed.ncbi.nlm.nih.gov/16601676","citation_count":91,"is_preprint":false},{"pmid":"16772376","id":"PMC_16772376","title":"A mechanism of translational repression by competition of Paip2 with eIF4G for poly(A) binding protein (PABP) binding.","date":"2006","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/16772376","citation_count":76,"is_preprint":false},{"pmid":"20739757","id":"PMC_20739757","title":"The poly(A)-binding protein partner Paip2a controls translation during late spermiogenesis in mice.","date":"2010","source":"The Journal of clinical investigation","url":"https://pubmed.ncbi.nlm.nih.gov/20739757","citation_count":59,"is_preprint":false},{"pmid":"16804161","id":"PMC_16804161","title":"Regulation of poly(A) binding protein function in translation: Characterization of the Paip2 homolog, Paip2B.","date":"2006","source":"RNA (New York, N.Y.)","url":"https://pubmed.ncbi.nlm.nih.gov/16804161","citation_count":46,"is_preprint":false},{"pmid":"30992367","id":"PMC_30992367","title":"Polyadenylate-binding protein-interacting proteins PAIP1 and PAIP2 affect translation termination.","date":"2019","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/30992367","citation_count":27,"is_preprint":false},{"pmid":"23964095","id":"PMC_23964095","title":"A new role for the cellular PABP repressor Paip2 as an innate restriction factor capable of limiting productive cytomegalovirus replication.","date":"2013","source":"Genes & development","url":"https://pubmed.ncbi.nlm.nih.gov/23964095","citation_count":21,"is_preprint":false},{"pmid":"22190698","id":"PMC_22190698","title":"PABP interacting protein 2A (PAIP2A) regulates specific key proteins during spermiogenesis in the mouse.","date":"2012","source":"Biology of reproduction","url":"https://pubmed.ncbi.nlm.nih.gov/22190698","citation_count":15,"is_preprint":false},{"pmid":"24293655","id":"PMC_24293655","title":"Poly(A) RNA and Paip2 act as allosteric regulators of poly(A)-binding protein.","date":"2013","source":"Nucleic acids research","url":"https://pubmed.ncbi.nlm.nih.gov/24293655","citation_count":13,"is_preprint":false},{"pmid":"31001806","id":"PMC_31001806","title":"Paip2 cooperates with Cbp80 at an active promoter and participates in RNA Polymerase II phosphorylation in Drosophila.","date":"2019","source":"FEBS letters","url":"https://pubmed.ncbi.nlm.nih.gov/31001806","citation_count":12,"is_preprint":false},{"pmid":"26187994","id":"PMC_26187994","title":"ROCK inhibition enhances microRNA function by promoting deadenylation of targeted mRNAs via increasing PAIP2 expression.","date":"2015","source":"Nucleic acids research","url":"https://pubmed.ncbi.nlm.nih.gov/26187994","citation_count":12,"is_preprint":false},{"pmid":"29995569","id":"PMC_29995569","title":"Paip2 is localized to active promoters and loaded onto nascent mRNA in Drosophila.","date":"2018","source":"Cell cycle (Georgetown, Tex.)","url":"https://pubmed.ncbi.nlm.nih.gov/29995569","citation_count":10,"is_preprint":false},{"pmid":"35307347","id":"PMC_35307347","title":"Paip2A inhibits translation by competitively binding to the RNA recognition motifs of PABPC1 and promoting its dissociation from the poly(A) tail.","date":"2022","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/35307347","citation_count":9,"is_preprint":false},{"pmid":"21957478","id":"PMC_21957478","title":"Suppression of cellular transformation by poly (A) binding protein interacting protein 2 (Paip2).","date":"2011","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/21957478","citation_count":7,"is_preprint":false},{"pmid":"39707855","id":"PMC_39707855","title":"[Drosophila melanogaster Paip2 Binds ENY2 and Interacts with the TREX-2 Complex in Histone mRNP Particles].","date":"2024","source":"Molekuliarnaia biologiia","url":"https://pubmed.ncbi.nlm.nih.gov/39707855","citation_count":1,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":8987,"output_tokens":3847,"usd":0.042333,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":11364,"output_tokens":4917,"usd":0.089872,"stage2_stop_reason":"end_turn"},"total_usd":0.132205,"stage1_batch_id":"msgbatch_013a8chtv3AWyTqv4z4sEF4C","stage2_batch_id":"msgbatch_01AHsuW63vinsvuTgzmQ3n62","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2001,\n      \"finding\": \"Paip2 is a novel PABP-interacting protein that represses translation both in vitro and in vivo by decreasing the affinity of PABP for polyadenylate RNA and disrupting the repeating structure of poly(A) RNP; it preferentially inhibits translation of poly(A)-containing mRNA but not cap- and eIF4G-independent HCV IRES-mediated translation. Paip2 also competes with Paip1 for PABP binding.\",\n      \"method\": \"In vitro translation assay, in vivo transfection, PABP-poly(A) binding assays, competition binding\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Strong — multiple orthogonal methods (in vitro translation, in vivo assays, binding assays) in a single rigorous study establishing mechanism\",\n      \"pmids\": [\"11172725\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"Paip2 contains two binding sites for PABP: a 16-amino-acid C-terminal stretch and a central region. PABP also has two binding regions for Paip2: the RRM region and the C-terminal region. The stoichiometry is 2:1 (Paip2:PABP), with two independent Kd values of 0.66 nM and 74 nM. Only the central Paip2 fragment (binding PABP RRM with high affinity) inhibits PABP-poly(A) binding and translation.\",\n      \"method\": \"Biacore surface plasmon resonance, far-Western analysis, deletion mapping\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — quantitative biophysical measurements (Biacore) combined with far-Western analysis, multiple orthogonal methods defining stoichiometry and binding domains\",\n      \"pmids\": [\"11438674\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Paip2 protein stability is regulated by the E3 ubiquitin ligase EDD: upon PABP depletion, Paip2 interacts with EDD, which ubiquitinates Paip2 and targets it for proteasomal degradation. Knockdown of EDD increases Paip2 stability. This establishes a homeostatic feedback loop whereby PABP levels regulate Paip2 turnover.\",\n      \"method\": \"RNAi knockdown of PABP and EDD, co-immunoprecipitation, ubiquitination assay, protein stability measurements\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal Co-IP, siRNA knockdown experiments with multiple readouts (ubiquitination assay, protein stability) in a single lab\",\n      \"pmids\": [\"16601676\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Paip2 inhibits translation by a second mechanism: competing with eIF4G for binding to PABP, independent of its ability to disrupt PABP-poly(A) interaction. This was demonstrated by showing Paip2 inhibits translation when PABP is tethered to the 3' end of mRNA (bypassing poly(A) displacement).\",\n      \"method\": \"In vitro translation assay with tethered PABP, competition binding assay\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Moderate — in vitro reconstitution with tethered PABP system and competition binding, demonstrating a distinct second mechanism in a single focused study\",\n      \"pmids\": [\"16772376\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"Paip2B (a homolog of Paip2A sharing 59% identity) inhibits translation of capped and polyadenylated mRNAs both in vitro and in vivo by displacing PABP from the poly(A) tail, similar to Paip2A. However, Paip2A is more highly ubiquitinated than Paip2B and is degraded more rapidly by the proteasome.\",\n      \"method\": \"In vitro translation assay, in vivo overexpression, ubiquitination assay, proteasome inhibitor treatment\",\n      \"journal\": \"RNA (New York, N.Y.)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple functional assays (in vitro translation, in vivo, ubiquitination) from a single lab comparing the two paralogs\",\n      \"pmids\": [\"16804161\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Paip2a knockout mice are male-infertile; Paip2a/Paip2b double-KO mice show inhibited translation of mRNAs encoding proteins essential for spermiogenesis in late spermatids. This is caused by aberrant PABP overexpression (due to loss of Paip2-mediated homeostasis), which impairs eIF4E interaction with the 5' cap structure.\",\n      \"method\": \"Knockout mouse generation, polysome profiling, Western blot, co-immunoprecipitation (eIF4E-cap interaction assay)\",\n      \"journal\": \"The Journal of clinical investigation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic KO with specific molecular phenotype (impaired eIF4E-cap interaction), replicated across single and double KO, multiple orthogonal methods\",\n      \"pmids\": [\"20739757\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Poly(A) RNA induces a conformational change in PABP in which RRM1 comes into proximity with RRM4, bending the region between RRM2 and RRM3. Paip2 disrupts this bent structure, converting PABP to an extended conformation and thereby inhibiting PABP-poly(A) binding.\",\n      \"method\": \"Single-molecule real-time visualization (FRET/single-molecule imaging) of individual PABP molecules\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — single-molecule imaging approach demonstrating conformational change, single lab, single method\",\n      \"pmids\": [\"24293655\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"During HCMV infection, Paip2 accumulates alongside PABP1 and EDD1 (via the viral UL38 mTORC1 activator), increases its association with PABP1, and acts as an innate restriction factor limiting viral protein synthesis. Depleting Paip2 restored eIF4F assembly and promoted viral replication without increasing PABP1.\",\n      \"method\": \"siRNA depletion of Paip2, co-immunoprecipitation, Western blot, viral replication assay, eIF4F assembly assay\",\n      \"journal\": \"Genes & development\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal methods (siRNA depletion, Co-IP, viral replication assay) in a single lab establishing a new functional role\",\n      \"pmids\": [\"23964095\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"PAIP2 prevents translation termination at premature termination codons by inhibiting PABP activity at its C-terminal domain. PAIP2 inhibits free PABP-stimulated translation termination in vitro; however, once PABP is bound to the poly(A) tail, it becomes insensitive to PAIP2 suppression and efficiently activates translation termination via eRF3a.\",\n      \"method\": \"In vitro translation termination reconstitution assay, biochemical competition experiments with purified components\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro reconstitution assay with purified components, clear positive and negative conditions tested, single lab\",\n      \"pmids\": [\"30992367\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"In Drosophila, nuclear Paip2 is part of an ~300-kDa protein complex and interacts with the mRNA capping factor (Cbp80) and factors of RNA Pol II transcription initiation and early elongation. Paip2 functionally cooperates with Cbp80 to ensure proper Pol II CTD Ser5 phosphorylation at the promoter.\",\n      \"method\": \"Co-immunoprecipitation, mass spectrometry, ChIP, Pol II CTD phosphorylation assay (Drosophila)\",\n      \"journal\": \"FEBS letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP with mass spectrometry plus functional CTD phosphorylation assay, single lab, Drosophila ortholog\",\n      \"pmids\": [\"31001806\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"In Drosophila, Paip2 is present in the nucleus and associates with chromatin at promoter regions of active genes via an RNA-dependent (indirect) interaction, suggesting Paip2 is recruited to mRNAs co-transcriptionally.\",\n      \"method\": \"Chromatin immunoprecipitation (ChIP), nuclear fractionation, RNase treatment, immunofluorescence in Drosophila tissues\",\n      \"journal\": \"Cell cycle (Georgetown, Tex.)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — ChIP and fractionation with RNase sensitivity controls, single lab, Drosophila ortholog\",\n      \"pmids\": [\"29995569\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Paip2A competitively binds the RRM2-RRM3 region of PABPC1 with Kd ~1 nM (comparable to poly(A) affinity). Mechanistically, Paip2A first binds RRM2 of poly(A)-bound PABPC1, and RRM2-anchored Paip2A then displaces RRM3 from poly(A), causing full dissociation of PABPC1 from the poly(A) tail.\",\n      \"method\": \"Isothermal titration calorimetry (ITC), NMR spectroscopy with structural analysis of RRM-ligand interactions\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — quantitative ITC plus NMR structural characterization, two orthogonal biophysical methods, mechanistic model validated in a single rigorous study\",\n      \"pmids\": [\"35307347\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"ROCK inhibitor treatment increases PAIP2 expression via transcriptional upregulation by HNF4A, facilitated by increased ROCK1 nuclear localization and ROCK1 association with HNF4A. Elevated PAIP2 enhances poly(A) shortening of miRNA-targeted mRNAs, globally upregulating miRNA function.\",\n      \"method\": \"ROCK inhibitor treatment, siRNA knockdown of PAIP2 and ROCK1, reporter assays for miRNA function, co-immunoprecipitation (ROCK1-HNF4A), nuclear fractionation\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 / Moderate — multiple experiments (Co-IP, nuclear fractionation, functional miRNA assays) from a single lab, but mechanism is indirect\",\n      \"pmids\": [\"26187994\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Paip2 overexpression suppresses Ras(V12)-induced cellular transformation (colony formation in semi-solid matrix and focus formation), and this activity requires Paip2's ability to bind PABP.\",\n      \"method\": \"Soft-agar colony formation assay, focus formation assay, PABP-binding mutant of Paip2\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 / Weak — functional transformation assays with mutant analysis, single lab, single study\",\n      \"pmids\": [\"21957478\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"In Drosophila, Paip2 directly binds ENY2 in vitro and interacts with the ENY2-containing TREX-2 complex in vivo. Paip2 is present at the histone gene locus and histone locus bodies (HLBs). Paip2 knockdown decreases TREX-2 subunit association with histone mRNP particles, suggesting Paip2 facilitates TREX-2 binding to histone mRNPs.\",\n      \"method\": \"Yeast two-hybrid, in vitro pull-down, co-immunoprecipitation, ChIP, RNA interference knockdown, RNP particle fractionation (Drosophila)\",\n      \"journal\": \"Molekuliarnaia biologiia\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 / Moderate — multiple methods (yeast two-hybrid, in vitro binding, Co-IP, RNAi knockdown) supporting a new nuclear function in Drosophila ortholog\",\n      \"pmids\": [\"39707855\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"PAIP2 (Paip2A) is a translational repressor that binds PABPC1 at two sites (primarily RRM2-RRM3) with ~1 nM affinity, competitively displacing PABP from the poly(A) tail by a sequential RRM2-anchoring/RRM3-displacement mechanism and also competing with eIF4G for PABP binding; PAIP2 protein stability is homeostatically regulated by the E3 ubiquitin ligase EDD in a PABP-dependent manner, its nuclear form participates in co-transcriptional mRNA processing and Pol II CTD Ser5 phosphorylation in Drosophila, and it is required for proper translational activation during late spermiogenesis in mice.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"PAIP2 (Paip2A) is a translational repressor that controls cytoplasmic translation by antagonizing poly(A)-binding protein (PABP/PABPC1) [#0]. It binds PABP at two sites via two contact regions on PABP and decreases PABP affinity for polyadenylate RNA, disrupting poly(A) RNP structure and selectively inhibiting translation of poly(A)-containing mRNAs while sparing cap- and eIF4G-independent IRES translation [#0, #1]. PAIP2 engages the RRM2–RRM3 region of PABPC1 with ~1 nM affinity and displaces it from poly(A) through a sequential mechanism in which RRM2-anchored PAIP2 dislodges RRM3 from the poly(A) tail [#11], reversing the bent, poly(A)-induced PABP conformation into an extended state [#6]. PAIP2 represses translation by a second, independent route: competing with eIF4G for PABP binding even when PABP is tethered to mRNA [#3], and it also blocks free PABP from stimulating eRF3a-dependent translation termination [#8]. PAIP2 abundance is set by a homeostatic feedback loop in which the E3 ubiquitin ligase EDD ubiquitinates PAIP2 for proteasomal degradation upon PABP depletion, coupling PAIP2 stability to PABP levels [#2]. Genetically, Paip2a/Paip2b loss in mice causes male infertility through aberrant PABP overexpression that impairs eIF4E–cap interaction and blocks the translational activation required for late spermiogenesis [#5]. Beyond its cytoplasmic role, a nuclear pool of the Drosophila ortholog associates co-transcriptionally with chromatin at active promoters and cooperates with capping and TREX-2 factors in mRNA processing [#9, #10, #14].\"\n}\n\n**Note:** Returning the full JSON object below.\n\n{\n  \"mechanistic_narrative\": \"PAIP2 (Paip2A) is a translational repressor that controls cytoplasmic translation by antagonizing poly(A)-binding protein (PABP/PABPC1) [#0]. It binds PABP at two sites via two contact regions on PABP and decreases PABP affinity for polyadenylate RNA, disrupting poly(A) RNP structure and selectively inhibiting translation of poly(A)-containing mRNAs while sparing cap- and eIF4G-independent IRES translation [#0, #1]. PAIP2 engages the RRM2–RRM3 region of PABPC1 with ~1 nM affinity and displaces it from poly(A) through a sequential mechanism in which RRM2-anchored PAIP2 dislodges RRM3 from the poly(A) tail [#11], reversing the bent, poly(A)-induced PABP conformation into an extended state [#6]. PAIP2 represses translation by a second, independent route: competing with eIF4G for PABP binding even when PABP is tethered to mRNA [#3], and it also blocks free PABP from stimulating eRF3a-dependent translation termination [#8]. PAIP2 abundance is set by a homeostatic feedback loop in which the E3 ubiquitin ligase EDD ubiquitinates PAIP2 for proteasomal degradation upon PABP depletion, coupling PAIP2 stability to PABP levels [#2]. Genetically, Paip2a/Paip2b loss in mice causes male infertility through aberrant PABP overexpression that impairs eIF4E–cap interaction and blocks the translational activation required for late spermiogenesis [#5]. Beyond its cytoplasmic role, a nuclear pool of the Drosophila ortholog associates co-transcriptionally with chromatin at active promoters and cooperates with capping and TREX-2 factors in mRNA processing [#9, #10, #14].\",\n  \"teleology\": [\n    {\n      \"year\": 2001,\n      \"claim\": \"Established that PAIP2 is a dedicated PABP-interacting translational repressor that works by lowering PABP affinity for the poly(A) tail, defining the gene's core biological role.\",\n      \"evidence\": \"In vitro translation assays, in vivo transfection, PABP–poly(A) binding and competition assays\",\n      \"pmids\": [\"11172725\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not define the structural basis or affinity of the PAIP2–PABP interaction\", \"Did not address how PAIP2 levels are regulated in cells\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"Quantified the bivalent PAIP2–PABP architecture, showing two binding sites on each partner with 2:1 stoichiometry and identifying the central PABP-RRM-binding fragment as the active repressive module.\",\n      \"evidence\": \"Biacore surface plasmon resonance, far-Western, deletion mapping\",\n      \"pmids\": [\"11438674\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not resolve the atomic-level RRM contacts\", \"Did not establish which interaction operates in vivo\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Revealed that PAIP2 abundance is homeostatically coupled to PABP via EDD-mediated ubiquitination and proteasomal degradation, explaining how repressor and target levels are balanced.\",\n      \"evidence\": \"RNAi knockdown of PABP and EDD, reciprocal Co-IP, ubiquitination and protein-stability assays\",\n      \"pmids\": [\"16601676\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not identify the ubiquitinated residues on PAIP2\", \"Did not establish how PABP binding shields PAIP2 from EDD\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Demonstrated a second, poly(A)-displacement-independent repression mechanism whereby PAIP2 competes with eIF4G for PABP, broadening the model beyond simple poly(A) release.\",\n      \"evidence\": \"In vitro translation with tethered PABP, competition binding\",\n      \"pmids\": [\"16772376\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not quantify the relative contribution of each mechanism in vivo\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Showed the paralog Paip2B represses translation by the same poly(A)-displacement mechanism but is more stable than the more heavily ubiquitinated Paip2A, distinguishing the two family members.\",\n      \"evidence\": \"In vitro/in vivo translation assays, ubiquitination assay, proteasome inhibition\",\n      \"pmids\": [\"16804161\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single-lab paralog comparison\", \"Did not establish distinct physiological roles for Paip2A vs Paip2B\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Provided in vivo genetic proof that PAIP2-mediated PABP homeostasis is essential, as its loss causes male infertility through PABP overexpression that impairs eIF4E–cap binding during spermiogenesis.\",\n      \"evidence\": \"Single and double knockout mice, polysome profiling, eIF4E–cap interaction Co-IP\",\n      \"pmids\": [\"20739757\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not define which spermatid mRNAs are directly affected\", \"Did not test roles in non-germline tissues\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Linked PAIP2's PABP-binding activity to tumor-suppressive function by showing it suppresses Ras-induced transformation in a PABP-binding-dependent manner.\",\n      \"evidence\": \"Soft-agar colony and focus formation assays with a PABP-binding mutant\",\n      \"pmids\": [\"21957478\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single study with cell-based transformation readouts only\", \"No in vivo tumor evidence\", \"Downstream mRNA targets not identified\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Provided a structural rationale for repression by showing poly(A) bends PABP and that PAIP2 disrupts this bent conformation to inhibit poly(A) binding.\",\n      \"evidence\": \"Single-molecule real-time imaging of individual PABP molecules\",\n      \"pmids\": [\"24293655\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single method, single lab\", \"Did not map the conformational change to specific RRM contacts\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Assigned PAIP2 an antiviral role as an innate restriction factor that limits eIF4F assembly and viral protein synthesis during HCMV infection.\",\n      \"evidence\": \"siRNA depletion, Co-IP, viral replication and eIF4F assembly assays\",\n      \"pmids\": [\"23964095\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Limited to HCMV context\", \"Did not establish breadth across other viruses\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Connected PAIP2 to miRNA function, showing transcriptional upregulation of PAIP2 via HNF4A enhances poly(A) shortening of miRNA-targeted mRNAs.\",\n      \"evidence\": \"ROCK inhibitor treatment, siRNA knockdown, miRNA reporter assays, Co-IP, nuclear fractionation\",\n      \"pmids\": [\"26187994\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanistic link is indirect\", \"Did not define how PAIP2 promotes deadenylation mechanistically\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Identified a nuclear, chromatin-associated pool of Paip2 recruited co-transcriptionally to active promoters via RNA-dependent interaction, extending PAIP2 beyond cytoplasmic translation.\",\n      \"evidence\": \"ChIP, nuclear fractionation, RNase treatment, immunofluorescence (Drosophila)\",\n      \"pmids\": [\"29995569\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Drosophila ortholog only\", \"Direct chromatin/RNA-binding partners not defined\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Refined the termination model, showing PAIP2 blocks free PABP from stimulating eRF3a-dependent termination but loses this control once PABP is poly(A)-bound.\",\n      \"evidence\": \"In vitro translation termination reconstitution with purified components\",\n      \"pmids\": [\"30992367\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Cellular relevance of premature termination control not established\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Defined a nuclear Paip2 complex linking it to mRNA capping and Pol II transcription, showing cooperation with Cbp80 for proper CTD Ser5 phosphorylation.\",\n      \"evidence\": \"Co-IP, mass spectrometry, ChIP, CTD phosphorylation assay (Drosophila)\",\n      \"pmids\": [\"31001806\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Drosophila ortholog only\", \"Whether human PAIP2 has an equivalent nuclear role is untested\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Resolved the molecular mechanism of poly(A) displacement, showing PAIP2A binds RRM2 first then displaces RRM3 from poly(A) with ~1 nM affinity comparable to poly(A) itself.\",\n      \"evidence\": \"Isothermal titration calorimetry and NMR structural analysis\",\n      \"pmids\": [\"35307347\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not capture a full-length complex structure\", \"Did not integrate eIF4G-competition mechanism structurally\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Extended the nuclear function by showing Paip2 binds ENY2 and the TREX-2 complex and facilitates TREX-2 association with histone mRNPs at histone locus bodies.\",\n      \"evidence\": \"Yeast two-hybrid, in vitro pull-down, Co-IP, ChIP, RNAi, RNP fractionation (Drosophila)\",\n      \"pmids\": [\"39707855\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Drosophila ortholog only\", \"Functional consequence for histone mRNA processing not quantified\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Whether the nuclear, co-transcriptional and TREX-2/histone-locus functions documented for the Drosophila ortholog are conserved in mammalian PAIP2 remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No direct evidence for human PAIP2 nuclear chromatin function\", \"Relationship between cytoplasmic repressor and nuclear roles undefined\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [0, 1, 3, 8, 11]},\n      {\"term_id\": \"GO:0045182\", \"supporting_discovery_ids\": [0, 3, 8]},\n      {\"term_id\": \"GO:0140313\", \"supporting_discovery_ids\": [0, 11]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [0, 5]},\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [9, 10]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-72766\", \"supporting_discovery_ids\": [0]},\n      {\"term_id\": \"R-HSA-8953854\", \"supporting_discovery_ids\": [0, 8, 12]},\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [2]}\n    ],\n    \"complexes\": [\"TREX-2\"],\n    \"partners\": [\"PABPC1\", \"EDD/UBR5\", \"eIF4G\", \"PAIP1\", \"ENY2\", \"Cbp80\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":7,"faith_total":7,"faith_pct":100.0}}