{"gene":"CDIPT","run_date":"2026-06-09T22:57:18","timeline":{"discoveries":[{"year":1996,"finding":"Rat phosphatidylinositol synthase (CDIPT/PIS) cDNA was cloned by functional complementation of the yeast pis mutation; the encoded 213-amino acid protein catalyzes formation of phosphatidylinositol and CMP from CDP-diacylglycerol and myo-inositol (EC 2.7.8.11), and is highly homologous to yeast phosphatidylinositol synthase.","method":"Functional complementation of yeast pis mutant with rat brain cDNA library; sequence analysis","journal":"FEBS letters","confidence":"High","confidence_rationale":"Tier 1 / Moderate — functional complementation (in vivo enzymatic rescue) with sequence verification; single lab but definitive demonstration of enzymatic identity","pmids":["8804431"],"is_preprint":false},{"year":1988,"finding":"Expression of the S. cerevisiae PIS gene (ortholog of CDIPT) in E. coli reconstituted phosphatidylinositol synthase activity; cells accumulated phosphatidylinositol (~4% of total phospholipids) at the expense of phosphatidylglycerol when supplemented with myo-inositol, directly demonstrating the enzymatic function of PIS in phosphatidylinositol biosynthesis.","method":"Heterologous expression in E. coli with lacZ fusion; phospholipid compositional analysis by labeling","journal":"Journal of bacteriology","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vivo enzymatic reconstitution in heterologous host with quantitative phospholipid analysis; foundational biochemical demonstration","pmids":["2844726"],"is_preprint":false},{"year":1995,"finding":"Mutation of His114 in the yeast Pis1 phosphatidylinositol synthase to Gln increased Km for myo-inositol; site-directed mutagenesis at codon 114 showed that Ala, Thr, and Leu substitutions supported growth while Asp, Lys, and Tyr substitutions did not; all mutant enzymes showed greatly reduced in vitro activity, identifying His114 as critical for catalytic function.","method":"Isolation of mutant PIS allele; oligonucleotide-mediated site-directed mutagenesis; in vitro enzyme activity assay in E. coli expression system; in vivo yeast growth assay","journal":"FEMS microbiology letters","confidence":"High","confidence_rationale":"Tier 1 / Moderate — active-site mutagenesis combined with both in vitro enzymatic assay and in vivo complementation; single lab but multiple orthogonal methods","pmids":["7896081"],"is_preprint":false},{"year":2005,"finding":"Zinc depletion in S. cerevisiae increases phosphatidylinositol synthase (Pis1p) activity, PIS1 mRNA, and Pis1p protein levels via a transcriptional mechanism; this regulation is mediated by the zinc-responsive transcription factor Zap1p, which directly binds a UAS zinc-responsive element in the PIS1 promoter. Mutations in this element abolished Zap1p-DNA interaction in vitro and zinc-mediated PIS1 regulation in vivo.","method":"Zinc depletion experiments; PIS1-lacZ reporter assay; zap1Δ and zrt1Δzrt2Δ mutant analysis; EMSA with GST-Zap1p and PIS1 promoter; site-directed mutagenesis of UAS zinc-responsive element","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — multiple orthogonal methods including EMSA, reporter assays, genetic mutants, and mutagenesis; single lab but comprehensive mechanistic dissection","pmids":["15980062"],"is_preprint":false},{"year":2003,"finding":"PIS1 promoter analysis in S. cerevisiae identified three upstream activating sequence (UAS) elements required for expression; deletion of UAS1 or UAS2 reduced expression ~45%, while deletion of UAS3 reduced it ~84%. UAS3 contains a Rox1p binding site; PIS1 expression is repressed under aerobic conditions in a Rox1p-dependent manner, and phosphatidylinositol levels are elevated under anaerobic conditions.","method":"Promoter deletion analysis; PIS1-cat reporter gene assays; rox1Δ mutant analysis; aerobic/anaerobic growth conditions","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — reporter gene deletion analysis with genetic (rox1Δ) validation; single lab, two orthogonal approaches","pmids":["12890676"],"is_preprint":false},{"year":2008,"finding":"PIS1 expression in S. cerevisiae is induced twofold by inositol through a mechanism requiring the transcriptional regulator Ume6p (but not the canonical Ino2p/Ino4p activators, though Ino4p is required for full expression); chromatin immunoprecipitation confirmed that Ume6p directly binds the PIS1 promoter and acts as a positive regulator.","method":"PIS1 reporter assays in ino2Δ, ino4Δ, ume6Δ mutants; chromatin immunoprecipitation (ChIP)","journal":"Molecular microbiology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic epistasis with reporter assays plus ChIP confirmation; single lab, two orthogonal methods","pmids":["19019152"],"is_preprint":false},{"year":2009,"finding":"Regulated reduction of PIS1 expression in S. cerevisiae (using a GAL1-PIS1 strain) demonstrated that phosphatidylinositol content correlates with PIS1 expression; as little as 4% phosphatidylinositol is sufficient for cell growth. Reduced PIS1 expression caused derepression of INO1, CHO1, and INO2, and overproduction of inositol (Opi- phenotype), consistent with phosphatidic acid acting as the regulatory signal.","method":"GAL1-inducible PIS1 expression system; phospholipid composition analysis; INO1/CHO1/INO2 reporter assays; inositol excretion assay","journal":"FEMS yeast research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — conditional expression system with multiple biochemical and genetic readouts; single lab, multiple orthogonal methods","pmids":["19456874"],"is_preprint":false},{"year":2006,"finding":"The PIS1 promoter in S. cerevisiae contains three upstream ATG codons in-frame with three stop codons located before the authentic start codon; mutation of the first ATG (ATG1) caused the largest increase in PIS1-lacZ reporter expression. RT-PCR confirmed that at least some PIS1 transcripts include all upstream AUG codons, and these negatively regulate PIS1 expression.","method":"Site-directed mutagenesis of upstream ATG codons; PIS1 promoter-lacZ reporter assays; RT-PCR","journal":"Biochemical and biophysical research communications","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — mutagenesis of translational control elements combined with reporter assays and RT-PCR; single lab","pmids":["16997274"],"is_preprint":false},{"year":2015,"finding":"The active site (CAPT motif) of yeast phosphatidylinositol synthase Pis1 faces the cytosol; cysteine accessibility experiments using membrane-impermeant and membrane-permeant maleimide reagents on native and Cys-free versions of Pis1 demonstrated cytosolic orientation of the catalytic domain. The central 84% of the Pis1 sequence aligns with six transmembrane helices of archaeal CAPT family crystal structures. Mild non-denaturing detergent (dodecylmaltoside at 0.05%) altered active-site Cys accessibility, and low concentrations inactivated the enzyme, indicating strong sensitivity of Pis1 structure to the lipid environment.","method":"Cysteine accessibility with membrane-permeant (NEM) and non-permeant maleimides; Cys-free Pis1 mutagenesis; in vitro enzyme activity assay; structural alignment to archaeal CAPT crystal structures","journal":"Biochimica et biophysica acta","confidence":"High","confidence_rationale":"Tier 1 / Moderate — topology mapped by cysteine accessibility with multiple maleimide reagents and Cys-free background, combined with enzymatic activity assays and structural homology modeling; single lab but multiple orthogonal methods","pmids":["25687304"],"is_preprint":false},{"year":2011,"finding":"Loss of cdipt function in zebrafish (hi559 insertional mutant) abrogates de novo phosphatidylinositol synthesis, causing hepatomegaly, macrovesicular steatosis, ballooning, and necroapoptosis. cdipt-deficient hepatocytes display marked ER architectural disruption and upregulation of ER stress markers (atf6, hspa5, calr, xbp1), revealing a mechanistic link between CDIPT-dependent phosphatidylinositol synthesis, ER stress, and hepatic steatosis.","method":"Zebrafish insertional mutant (cdipthi559Tg/+); phospholipid synthesis assay; microarray gene expression profiling with GSEA; ER stress marker RT-PCR; ultrastructural EM; tunicamycin ER stress induction in wild-type as phenocopy","journal":"Hepatology (Baltimore, Md.)","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic loss-of-function with multiple orthogonal readouts (lipid synthesis, transcriptomics, EM ultrastructure, pharmacological phenocopy); single lab but comprehensive","pmids":["21488074"],"is_preprint":false},{"year":2022,"finding":"In Candida albicans, phosphatidylinositol synthase Pis1 localizes to the endoplasmic reticulum (demonstrated by GFP tagging); PIS1 is essential for normal growth. Overexpression of PIS1 increased sensitivity to ER stress and cell wall stress, downregulated ER stress response and cell wall integrity genes, enhanced secretion of extracellular hydrolases, and increased fungal virulence in a mouse infection model.","method":"GFP tagging and live-cell imaging for ER localization; MET3 promoter-regulated knockdown; PIS1 overexpression; ER stress/cell wall stress assays; mouse infection virulence model; gene expression analysis","journal":"Fungal genetics and biology : FG & B","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct ER localization by GFP imaging, essential gene validation by conditional knockdown, and overexpression with multiple functional readouts; single lab","pmids":["35227874"],"is_preprint":false}],"current_model":"CDIPT (phosphatidylinositol synthase) is an endoplasmic reticulum-resident enzyme whose cytosol-facing active site (CAPT motif) catalyzes the CDP-diacylglycerol- and myo-inositol-dependent synthesis of phosphatidylinositol and CMP; a conserved His residue (His114 in yeast) is critical for catalysis, expression is transcriptionally regulated by zinc (via Zap1p), oxygen (via Rox1p), inositol (via Ume6p), and upstream AUG-mediated translational attenuation, and loss of CDIPT function in vivo (zebrafish and Candida models) abolishes de novo phosphatidylinositol synthesis, triggers ER stress, and causes downstream pathologies including hepatic steatosis."},"narrative":{"mechanistic_narrative":"CDIPT is the endoplasmic reticulum-resident phosphatidylinositol synthase that catalyzes de novo synthesis of phosphatidylinositol and CMP from CDP-diacylglycerol and myo-inositol (EC 2.7.8.11), as established by functional complementation of the yeast pis mutant with rat cDNA and by reconstitution of enzymatic activity in heterologous hosts [PMID:8804431, PMID:2844726]. The catalytic CAPT-motif active site faces the cytosol, the enzyme aligns with six transmembrane helices of the archaeal CAPT family, and its structure and activity are strongly sensitive to the surrounding lipid environment [PMID:25687304]; a conserved histidine (His114 in yeast) is critical for catalysis, with substitutions raising the Km for myo-inositol or abolishing activity [PMID:7896081]. Expression of the yeast ortholog PIS1 is multiply controlled — induced by zinc depletion via direct Zap1p binding to a promoter zinc-responsive element [PMID:15980062], repressed aerobically through a Rox1p site [PMID:12890676], induced by inositol via Ume6p [PMID:19019152], and attenuated by upstream in-frame AUG codons in the transcript [PMID:16997274] — and phosphatidylinositol content tracks PIS1 expression, with phosphatidic acid serving as the regulatory signal coupling synthesis to inositol homeostasis [PMID:19456874]. Loss of CDIPT function in vivo abolishes de novo phosphatidylinositol synthesis, disrupts ER architecture, triggers the ER stress response, and produces hepatic steatosis in zebrafish [PMID:21488074], while the enzyme is essential for normal growth and modulates ER/cell-wall stress responses and virulence in Candida albicans [PMID:35227874].","teleology":[{"year":1988,"claim":"Established that the PIS gene product is itself the catalytic phosphatidylinositol synthase, resolving whether PIS encoded the enzyme or a regulator.","evidence":"Heterologous expression of S. cerevisiae PIS in E. coli with phospholipid compositional analysis","pmids":["2844726"],"confidence":"High","gaps":["No mammalian gene identified at this point","Active-site residues and topology unmapped"]},{"year":1995,"claim":"Identified His114 as a catalytically critical residue, providing the first residue-level mechanistic insight into the active site.","evidence":"Site-directed mutagenesis of yeast Pis1 with in vitro activity assays and in vivo growth complementation","pmids":["7896081"],"confidence":"High","gaps":["No structure to place His114 in catalytic mechanism","Role in substrate binding vs catalysis not fully resolved"]},{"year":1996,"claim":"Cloned the mammalian (rat) ortholog and confirmed conserved enzymatic identity, extending the yeast biochemistry to vertebrates.","evidence":"Functional complementation of yeast pis mutant with rat brain cDNA library and sequence analysis","pmids":["8804431"],"confidence":"High","gaps":["No characterization of mammalian regulation or physiology","Subcellular localization not directly demonstrated"]},{"year":2003,"claim":"Defined oxygen-responsive transcriptional control via Rox1p, linking phosphatidylinositol synthesis to aerobic/anaerobic state.","evidence":"PIS1 promoter deletion and reporter assays with rox1Δ mutant analysis under aerobic/anaerobic conditions in yeast","pmids":["12890676"],"confidence":"Medium","gaps":["Direct Rox1p binding not shown by EMSA/ChIP here","Conservation of oxygen regulation in mammals untested"]},{"year":2005,"claim":"Showed zinc availability regulates PIS1 transcription through direct Zap1p binding, connecting phospholipid synthesis to metal homeostasis.","evidence":"Zinc depletion, reporter assays, zap1Δ mutants, EMSA, and promoter element mutagenesis in yeast","pmids":["15980062"],"confidence":"High","gaps":["Physiological rationale for zinc coupling not fully defined","Mammalian relevance unknown"]},{"year":2006,"claim":"Revealed translational attenuation of PIS1 by upstream in-frame AUG codons, adding a post-transcriptional layer of expression control.","evidence":"Mutagenesis of upstream ATG codons, promoter-lacZ reporter assays, and RT-PCR in yeast","pmids":["16997274"],"confidence":"Medium","gaps":["Mechanism of ribosome reinitiation/leaky scanning not dissected","Conservation of uORF control unknown"]},{"year":2008,"claim":"Identified inositol-responsive induction via Ume6p, integrating PIS1 into inositol-dependent regulation of phospholipid genes.","evidence":"Reporter assays in ino2Δ/ino4Δ/ume6Δ mutants with ChIP confirmation of Ume6p promoter binding in yeast","pmids":["19019152"],"confidence":"Medium","gaps":["Ume6p acting as positive rather than typical repressor not mechanistically explained","Crosstalk with Ino2/Ino4 pathway incomplete"]},{"year":2009,"claim":"Demonstrated that phosphatidylinositol content tracks PIS1 dosage and that altered synthesis feeds back on inositol regulatory genes through phosphatidic acid signaling.","evidence":"GAL1-inducible PIS1 expression, phospholipid analysis, INO1/CHO1/INO2 reporters, and inositol excretion assays in yeast","pmids":["19456874"],"confidence":"Medium","gaps":["Direct demonstration that phosphatidic acid is the signal not shown","Minimal phosphatidylinositol threshold for specific pathways undefined"]},{"year":2011,"claim":"Connected loss of CDIPT-dependent phosphatidylinositol synthesis to ER stress and hepatic steatosis in a vertebrate, establishing physiological consequence of enzyme deficiency.","evidence":"Zebrafish cdipt insertional mutant with lipid synthesis assays, transcriptomics, EM ultrastructure, and tunicamycin phenocopy","pmids":["21488074"],"confidence":"High","gaps":["Causal chain from phosphatidylinositol loss to specific ER stress arms not dissected","Human disease association not established here"]},{"year":2015,"claim":"Mapped the cytosolic orientation of the CAPT catalytic domain and demonstrated lipid-environment dependence, defining the enzyme's membrane topology.","evidence":"Cysteine accessibility with permeant/non-permeant maleimides, Cys-free Pis1, activity assays, and structural alignment to archaeal CAPT structures","pmids":["25687304"],"confidence":"High","gaps":["No experimental high-resolution structure of the eukaryotic enzyme","Mechanism of lipid-dependent inactivation unresolved"]},{"year":2022,"claim":"Confirmed ER localization and essentiality of the enzyme in a fungal pathogen and linked its dosage to stress responses and virulence.","evidence":"GFP imaging, conditional knockdown, overexpression with ER/cell-wall stress assays, and mouse infection model in Candida albicans","pmids":["35227874"],"confidence":"Medium","gaps":["Molecular basis linking PIS1 dosage to virulence not defined","Relevance of overexpression phenotypes to native regulation unclear"]},{"year":null,"claim":"How CDIPT regulation, topology, and lipid sensitivity operate in mammalian cells and whether loss-of-function causes human disease remain to be established.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No mammalian regulatory mechanisms characterized in the corpus","No human Mendelian disease link in the timeline","No high-resolution structure of the eukaryotic enzyme"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0016740","term_label":"transferase activity","supporting_discovery_ids":[0,1,2,8]}],"localization":[{"term_id":"GO:0005783","term_label":"endoplasmic reticulum","supporting_discovery_ids":[9,10]}],"pathway":[{"term_id":"R-HSA-1430728","term_label":"Metabolism","supporting_discovery_ids":[0,1,6]}],"complexes":[],"partners":[],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"O14735","full_name":"CDP-diacylglycerol--inositol 3-phosphatidyltransferase","aliases":["Phosphatidylinositol synthase","PI synthase","PtdIns synthase"],"length_aa":213,"mass_kda":23.5,"function":"Catalyzes the biosynthesis of phosphatidylinositol (PtdIns) as well as PtdIns:inositol exchange reaction. May thus act to reduce an excessive cellular PtdIns content. The exchange activity is due to the reverse reaction of PtdIns synthase and is dependent on CMP, which is tightly bound to the enzyme","subcellular_location":"Endoplasmic reticulum membrane; Cell membrane","url":"https://www.uniprot.org/uniprotkb/O14735/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":true,"resolved_as":"","url":"https://depmap.org/portal/gene/CDIPT","classification":"Common Essential","n_dependent_lines":1005,"n_total_lines":1208,"dependency_fraction":0.831953642384106},"opencell":{"profiled":true,"resolved_as":"","ensg_id":"ENSG00000103502","cell_line_id":"CID000347","localizations":[{"compartment":"er","grade":3},{"compartment":"vesicles","grade":3},{"compartment":"golgi","grade":2}],"interactors":[{"gene":"PPP1R9B","stoichiometry":0.2},{"gene":"AGPAT6","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/target/CID000347","total_profiled":1310},"omim":[{"mim_id":"605893","title":"CDP-DIACYLGLYCEROL-INOSITOL 3-PHOSPHATIDYLTRANSFERASE; CDIPT","url":"https://www.omim.org/entry/605893"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Nucleoplasm","reliability":"Approved"},{"location":"Nuclear membrane","reliability":"Approved"},{"location":"Plasma membrane","reliability":"Approved"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/CDIPT"},"hgnc":{"alias_symbol":["PIS1","PIS"],"prev_symbol":[]},"alphafold":{"accession":"O14735","domains":[{"cath_id":"-","chopping":"1-86","consensus_level":"medium","plddt":93.6391,"start":1,"end":86},{"cath_id":"-","chopping":"90-213","consensus_level":"medium","plddt":86.8904,"start":90,"end":213}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/O14735","model_url":"https://alphafold.ebi.ac.uk/files/AF-O14735-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-O14735-F1-predicted_aligned_error_v6.png","plddt_mean":90.0},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=CDIPT","jax_strain_url":"https://www.jax.org/strain/search?query=CDIPT"},"sequence":{"accession":"O14735","fasta_url":"https://rest.uniprot.org/uniprotkb/O14735.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/O14735/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/O14735"}},"corpus_meta":[{"pmid":"2388320","id":"PMC_2388320","title":"The 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Mutations in this element abolished Zap1p-DNA interaction in vitro and zinc-mediated PIS1 regulation in vivo.\",\n      \"method\": \"Zinc depletion experiments; PIS1-lacZ reporter assay; zap1Δ and zrt1Δzrt2Δ mutant analysis; EMSA with GST-Zap1p and PIS1 promoter; site-directed mutagenesis of UAS zinc-responsive element\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — multiple orthogonal methods including EMSA, reporter assays, genetic mutants, and mutagenesis; single lab but comprehensive mechanistic dissection\",\n      \"pmids\": [\"15980062\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"PIS1 promoter analysis in S. cerevisiae identified three upstream activating sequence (UAS) elements required for expression; deletion of UAS1 or UAS2 reduced expression ~45%, while deletion of UAS3 reduced it ~84%. UAS3 contains a Rox1p binding site; PIS1 expression is repressed under aerobic conditions in a Rox1p-dependent manner, and phosphatidylinositol levels are elevated under anaerobic conditions.\",\n      \"method\": \"Promoter deletion analysis; PIS1-cat reporter gene assays; rox1Δ mutant analysis; aerobic/anaerobic growth conditions\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reporter gene deletion analysis with genetic (rox1Δ) validation; single lab, two orthogonal approaches\",\n      \"pmids\": [\"12890676\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"PIS1 expression in S. cerevisiae is induced twofold by inositol through a mechanism requiring the transcriptional regulator Ume6p (but not the canonical Ino2p/Ino4p activators, though Ino4p is required for full expression); chromatin immunoprecipitation confirmed that Ume6p directly binds the PIS1 promoter and acts as a positive regulator.\",\n      \"method\": \"PIS1 reporter assays in ino2Δ, ino4Δ, ume6Δ mutants; chromatin immunoprecipitation (ChIP)\",\n      \"journal\": \"Molecular microbiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic epistasis with reporter assays plus ChIP confirmation; single lab, two orthogonal methods\",\n      \"pmids\": [\"19019152\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"Regulated reduction of PIS1 expression in S. cerevisiae (using a GAL1-PIS1 strain) demonstrated that phosphatidylinositol content correlates with PIS1 expression; as little as 4% phosphatidylinositol is sufficient for cell growth. Reduced PIS1 expression caused derepression of INO1, CHO1, and INO2, and overproduction of inositol (Opi- phenotype), consistent with phosphatidic acid acting as the regulatory signal.\",\n      \"method\": \"GAL1-inducible PIS1 expression system; phospholipid composition analysis; INO1/CHO1/INO2 reporter assays; inositol excretion assay\",\n      \"journal\": \"FEMS yeast research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — conditional expression system with multiple biochemical and genetic readouts; single lab, multiple orthogonal methods\",\n      \"pmids\": [\"19456874\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"The PIS1 promoter in S. cerevisiae contains three upstream ATG codons in-frame with three stop codons located before the authentic start codon; mutation of the first ATG (ATG1) caused the largest increase in PIS1-lacZ reporter expression. RT-PCR confirmed that at least some PIS1 transcripts include all upstream AUG codons, and these negatively regulate PIS1 expression.\",\n      \"method\": \"Site-directed mutagenesis of upstream ATG codons; PIS1 promoter-lacZ reporter assays; RT-PCR\",\n      \"journal\": \"Biochemical and biophysical research communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — mutagenesis of translational control elements combined with reporter assays and RT-PCR; single lab\",\n      \"pmids\": [\"16997274\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"The active site (CAPT motif) of yeast phosphatidylinositol synthase Pis1 faces the cytosol; cysteine accessibility experiments using membrane-impermeant and membrane-permeant maleimide reagents on native and Cys-free versions of Pis1 demonstrated cytosolic orientation of the catalytic domain. The central 84% of the Pis1 sequence aligns with six transmembrane helices of archaeal CAPT family crystal structures. Mild non-denaturing detergent (dodecylmaltoside at 0.05%) altered active-site Cys accessibility, and low concentrations inactivated the enzyme, indicating strong sensitivity of Pis1 structure to the lipid environment.\",\n      \"method\": \"Cysteine accessibility with membrane-permeant (NEM) and non-permeant maleimides; Cys-free Pis1 mutagenesis; in vitro enzyme activity assay; structural alignment to archaeal CAPT crystal structures\",\n      \"journal\": \"Biochimica et biophysica acta\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — topology mapped by cysteine accessibility with multiple maleimide reagents and Cys-free background, combined with enzymatic activity assays and structural homology modeling; single lab but multiple orthogonal methods\",\n      \"pmids\": [\"25687304\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Loss of cdipt function in zebrafish (hi559 insertional mutant) abrogates de novo phosphatidylinositol synthesis, causing hepatomegaly, macrovesicular steatosis, ballooning, and necroapoptosis. cdipt-deficient hepatocytes display marked ER architectural disruption and upregulation of ER stress markers (atf6, hspa5, calr, xbp1), revealing a mechanistic link between CDIPT-dependent phosphatidylinositol synthesis, ER stress, and hepatic steatosis.\",\n      \"method\": \"Zebrafish insertional mutant (cdipthi559Tg/+); phospholipid synthesis assay; microarray gene expression profiling with GSEA; ER stress marker RT-PCR; ultrastructural EM; tunicamycin ER stress induction in wild-type as phenocopy\",\n      \"journal\": \"Hepatology (Baltimore, Md.)\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic loss-of-function with multiple orthogonal readouts (lipid synthesis, transcriptomics, EM ultrastructure, pharmacological phenocopy); single lab but comprehensive\",\n      \"pmids\": [\"21488074\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"In Candida albicans, phosphatidylinositol synthase Pis1 localizes to the endoplasmic reticulum (demonstrated by GFP tagging); PIS1 is essential for normal growth. Overexpression of PIS1 increased sensitivity to ER stress and cell wall stress, downregulated ER stress response and cell wall integrity genes, enhanced secretion of extracellular hydrolases, and increased fungal virulence in a mouse infection model.\",\n      \"method\": \"GFP tagging and live-cell imaging for ER localization; MET3 promoter-regulated knockdown; PIS1 overexpression; ER stress/cell wall stress assays; mouse infection virulence model; gene expression analysis\",\n      \"journal\": \"Fungal genetics and biology : FG & B\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct ER localization by GFP imaging, essential gene validation by conditional knockdown, and overexpression with multiple functional readouts; single lab\",\n      \"pmids\": [\"35227874\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"CDIPT (phosphatidylinositol synthase) is an endoplasmic reticulum-resident enzyme whose cytosol-facing active site (CAPT motif) catalyzes the CDP-diacylglycerol- and myo-inositol-dependent synthesis of phosphatidylinositol and CMP; a conserved His residue (His114 in yeast) is critical for catalysis, expression is transcriptionally regulated by zinc (via Zap1p), oxygen (via Rox1p), inositol (via Ume6p), and upstream AUG-mediated translational attenuation, and loss of CDIPT function in vivo (zebrafish and Candida models) abolishes de novo phosphatidylinositol synthesis, triggers ER stress, and causes downstream pathologies including hepatic steatosis.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"CDIPT is the endoplasmic reticulum-resident phosphatidylinositol synthase that catalyzes de novo synthesis of phosphatidylinositol and CMP from CDP-diacylglycerol and myo-inositol (EC 2.7.8.11), as established by functional complementation of the yeast pis mutant with rat cDNA and by reconstitution of enzymatic activity in heterologous hosts [#0, #1]. The catalytic CAPT-motif active site faces the cytosol, the enzyme aligns with six transmembrane helices of the archaeal CAPT family, and its structure and activity are strongly sensitive to the surrounding lipid environment [#8]; a conserved histidine (His114 in yeast) is critical for catalysis, with substitutions raising the Km for myo-inositol or abolishing activity [#2]. Expression of the yeast ortholog PIS1 is multiply controlled — induced by zinc depletion via direct Zap1p binding to a promoter zinc-responsive element [#3], repressed aerobically through a Rox1p site [#4], induced by inositol via Ume6p [#5], and attenuated by upstream in-frame AUG codons in the transcript [#7] — and phosphatidylinositol content tracks PIS1 expression, with phosphatidic acid serving as the regulatory signal coupling synthesis to inositol homeostasis [#6]. Loss of CDIPT function in vivo abolishes de novo phosphatidylinositol synthesis, disrupts ER architecture, triggers the ER stress response, and produces hepatic steatosis in zebrafish [#9], while the enzyme is essential for normal growth and modulates ER/cell-wall stress responses and virulence in Candida albicans [#10].\",\n  \"teleology\": [\n    {\n      \"year\": 1988,\n      \"claim\": \"Established that the PIS gene product is itself the catalytic phosphatidylinositol synthase, resolving whether PIS encoded the enzyme or a regulator.\",\n      \"evidence\": \"Heterologous expression of S. cerevisiae PIS in E. coli with phospholipid compositional analysis\",\n      \"pmids\": [\"2844726\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No mammalian gene identified at this point\", \"Active-site residues and topology unmapped\"]\n    },\n    {\n      \"year\": 1995,\n      \"claim\": \"Identified His114 as a catalytically critical residue, providing the first residue-level mechanistic insight into the active site.\",\n      \"evidence\": \"Site-directed mutagenesis of yeast Pis1 with in vitro activity assays and in vivo growth complementation\",\n      \"pmids\": [\"7896081\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No structure to place His114 in catalytic mechanism\", \"Role in substrate binding vs catalysis not fully resolved\"]\n    },\n    {\n      \"year\": 1996,\n      \"claim\": \"Cloned the mammalian (rat) ortholog and confirmed conserved enzymatic identity, extending the yeast biochemistry to vertebrates.\",\n      \"evidence\": \"Functional complementation of yeast pis mutant with rat brain cDNA library and sequence analysis\",\n      \"pmids\": [\"8804431\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No characterization of mammalian regulation or physiology\", \"Subcellular localization not directly demonstrated\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Defined oxygen-responsive transcriptional control via Rox1p, linking phosphatidylinositol synthesis to aerobic/anaerobic state.\",\n      \"evidence\": \"PIS1 promoter deletion and reporter assays with rox1\\u0394 mutant analysis under aerobic/anaerobic conditions in yeast\",\n      \"pmids\": [\"12890676\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct Rox1p binding not shown by EMSA/ChIP here\", \"Conservation of oxygen regulation in mammals untested\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Showed zinc availability regulates PIS1 transcription through direct Zap1p binding, connecting phospholipid synthesis to metal homeostasis.\",\n      \"evidence\": \"Zinc depletion, reporter assays, zap1\\u0394 mutants, EMSA, and promoter element mutagenesis in yeast\",\n      \"pmids\": [\"15980062\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Physiological rationale for zinc coupling not fully defined\", \"Mammalian relevance unknown\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Revealed translational attenuation of PIS1 by upstream in-frame AUG codons, adding a post-transcriptional layer of expression control.\",\n      \"evidence\": \"Mutagenesis of upstream ATG codons, promoter-lacZ reporter assays, and RT-PCR in yeast\",\n      \"pmids\": [\"16997274\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism of ribosome reinitiation/leaky scanning not dissected\", \"Conservation of uORF control unknown\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Identified inositol-responsive induction via Ume6p, integrating PIS1 into inositol-dependent regulation of phospholipid genes.\",\n      \"evidence\": \"Reporter assays in ino2\\u0394/ino4\\u0394/ume6\\u0394 mutants with ChIP confirmation of Ume6p promoter binding in yeast\",\n      \"pmids\": [\"19019152\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Ume6p acting as positive rather than typical repressor not mechanistically explained\", \"Crosstalk with Ino2/Ino4 pathway incomplete\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Demonstrated that phosphatidylinositol content tracks PIS1 dosage and that altered synthesis feeds back on inositol regulatory genes through phosphatidic acid signaling.\",\n      \"evidence\": \"GAL1-inducible PIS1 expression, phospholipid analysis, INO1/CHO1/INO2 reporters, and inositol excretion assays in yeast\",\n      \"pmids\": [\"19456874\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct demonstration that phosphatidic acid is the signal not shown\", \"Minimal phosphatidylinositol threshold for specific pathways undefined\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Connected loss of CDIPT-dependent phosphatidylinositol synthesis to ER stress and hepatic steatosis in a vertebrate, establishing physiological consequence of enzyme deficiency.\",\n      \"evidence\": \"Zebrafish cdipt insertional mutant with lipid synthesis assays, transcriptomics, EM ultrastructure, and tunicamycin phenocopy\",\n      \"pmids\": [\"21488074\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Causal chain from phosphatidylinositol loss to specific ER stress arms not dissected\", \"Human disease association not established here\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Mapped the cytosolic orientation of the CAPT catalytic domain and demonstrated lipid-environment dependence, defining the enzyme's membrane topology.\",\n      \"evidence\": \"Cysteine accessibility with permeant/non-permeant maleimides, Cys-free Pis1, activity assays, and structural alignment to archaeal CAPT structures\",\n      \"pmids\": [\"25687304\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No experimental high-resolution structure of the eukaryotic enzyme\", \"Mechanism of lipid-dependent inactivation unresolved\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Confirmed ER localization and essentiality of the enzyme in a fungal pathogen and linked its dosage to stress responses and virulence.\",\n      \"evidence\": \"GFP imaging, conditional knockdown, overexpression with ER/cell-wall stress assays, and mouse infection model in Candida albicans\",\n      \"pmids\": [\"35227874\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Molecular basis linking PIS1 dosage to virulence not defined\", \"Relevance of overexpression phenotypes to native regulation unclear\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How CDIPT regulation, topology, and lipid sensitivity operate in mammalian cells and whether loss-of-function causes human disease remain to be established.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No mammalian regulatory mechanisms characterized in the corpus\", \"No human Mendelian disease link in the timeline\", \"No high-resolution structure of the eukaryotic enzyme\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0016740\", \"supporting_discovery_ids\": [0, 1, 2, 8]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005783\", \"supporting_discovery_ids\": [9, 10]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-1430728\", \"supporting_discovery_ids\": [0, 1, 6]}\n    ],\n    \"complexes\": [],\n    \"partners\": [],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":4,"faith_total":4,"faith_pct":100.0}}