{"gene":"TG_247460","gene_symbol":"PCNA1","run_date":"2026-09-08T12:58:25","timeline":{"discoveries":[{"year":2000,"finding":"TgPCNA1 encodes a ~40 kDa protein expressed in T. gondii tachyzoites; two distinct PCNA genes (TgPCNA1 and TgPCNA2) exist in T. gondii genomic DNA, likely arising from gene duplication in the common ancestor of apicomplexans. TgPCNA1 and PfPCNA1 share 49% amino acid identity, higher than intraspecies PCNA pairs (27–30%).","method":"cDNA library screening, Southern blot, Northern blot, Western blot with specific antibodies, phylogenetic analysis","journal":"Molecular and biochemical parasitology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal methods (Southern, Northern, Western blot) in a single study establishing gene identity and protein expression, but no functional reconstitution or localization with functional consequence","pmids":["10960171"],"is_preprint":false,"attribution":[{"species":"Toxoplasma gondii","strain":"Type I"},{"species":"Toxoplasma gondii","strain":"Type II"},{"species":"Toxoplasma gondii","strain":"Type III"}]},{"year":2005,"finding":"TgPCNA1 is constitutively concentrated in the nucleus throughout all cell cycle phases in tachyzoites, including during S-phase where it displays a punctate pattern consistent with assembly into replication foci.","method":"Indirect immunofluorescence with TgPCNA1-GFP fusion protein and cell cycle staging","journal":"Molecular and biochemical parasitology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct live-cell and immunofluorescence localization across cell cycle phases, single lab","pmids":["15878790"],"is_preprint":false,"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2005,"finding":"Heterologous expression of TgPCNA1, but not TgPCNA2, complemented a POL30 (PCNA) cold-sensitive yeast mutant, indicating TgPCNA1 is functionally equivalent to canonical eukaryotic PCNA and likely serves as the major replisomal factor in T. gondii.","method":"Yeast complementation assay using cold-sensitive POL30 mutant strain","journal":"Molecular and biochemical parasitology","confidence":"High","confidence_rationale":"Tier 1 / Moderate — functional complementation in a defined genetic background with a clear phenotypic readout; single lab but direct functional test","pmids":["15878790"],"is_preprint":false,"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2005,"finding":"The TgPCNA1 gene could not be disrupted in tachyzoites, indicating it is essential for tachyzoite stage growth, consistent with its role as the primary replisomal PCNA.","method":"Gene disruption/knockout attempts in transgenic parasites","journal":"Molecular and biochemical parasitology","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — failure to disrupt the gene is consistent with essentiality but relies on a negative genetic result in a single lab study","pmids":["15878790"],"is_preprint":false,"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2025,"finding":"TgPCNA1 tagged with NeonGreen exhibits varied, dynamic subcellular localization across cell cycle phases, with DNA replication (detected by TgPCNA1 signal) initiating at or near centromeric regions and following a bell-shaped dynamic. TgPCNA1 was validated as a functional FUCCI probe for marking the S-phase in T. gondii tachyzoites.","method":"Quantitative live-cell imaging and immunofluorescence microscopy using TgPCNA1-NeonGreen in the auxin-induced degradation parental strain (ToxoFUCCIS system)","journal":"mBio","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct live-cell imaging with functional validation as a cell cycle marker, single lab with quantitative microscopy","pmids":["40590555"],"is_preprint":false,"attribution":[{"species":"Toxoplasma gondii","strain":""}]}],"current_model":"TgPCNA1 is an essential, nuclear-localized proliferating cell nuclear antigen in Toxoplasma gondii tachyzoites that functions as the primary replisomal clamp (as demonstrated by yeast complementation), localizes constitutively in the nucleus with punctate replication foci during S-phase initiating near centromeres, and is distinguished from the non-essential TgPCNA2 paralog by its continuous nuclear presence throughout the cell cycle and its indispensability for tachyzoite growth."},"narrative":{"mechanistic_narrative":"TgPCNA1 is the primary replisomal proliferating cell nuclear antigen of Toxoplasma gondii, functioning as the essential DNA replication clamp in the tachyzoite stage [PMID:10960171, PMID:15878790]. It is one of two PCNA paralogs (TgPCNA1 and TgPCNA2) that arose from an ancestral apicomplexan gene duplication [PMID:10960171]. Heterologous expression of TgPCNA1, but not TgPCNA2, rescues a cold-sensitive yeast POL30 mutant, establishing it as the functional equivalent of canonical eukaryotic PCNA and the major replisomal factor [PMID:15878790]. TgPCNA1 is constitutively nuclear across all cell cycle phases and reorganizes into punctate replication foci during S-phase, with DNA replication initiating at or near centromeric regions [PMID:15878790, PMID:40590555]. The gene cannot be disrupted in tachyzoites, indicating it is essential for growth [PMID:15878790], and its S-phase-specific dynamics have been exploited to build it into a FUCCI cell cycle probe [PMID:40590555]. Beyond its role as a replication clamp, the interacting partners and post-translational regulation of TgPCNA1 have not been characterized in the available corpus.","teleology":[{"year":2000,"claim":"Establishing that T. gondii carries two distinct PCNA genes defined the genetic architecture of the parasite's replication clamp machinery and raised the question of functional division between the paralogs.","evidence":"cDNA library screening with Southern, Northern, and Western blotting plus phylogenetic analysis of TgPCNA1/TgPCNA2 in tachyzoites","pmids":["10960171"],"confidence":"Medium","gaps":["Did not determine which paralog is the functional replisomal clamp","No localization or essentiality data","Roles of the two paralogs left undefined"],"attribution":[{"species":"Toxoplasma gondii","strain":"Type I"},{"species":"Toxoplasma gondii","strain":"Type II"},{"species":"Toxoplasma gondii","strain":"Type III"}]},{"year":2005,"claim":"Yeast complementation resolved which paralog is the canonical clamp by showing TgPCNA1, but not TgPCNA2, restores POL30 function, assigning TgPCNA1 the role of major replisomal PCNA.","evidence":"Complementation of a cold-sensitive POL30 yeast mutant with heterologously expressed TgPCNA1 vs TgPCNA2","pmids":["15878790"],"confidence":"High","gaps":["Does not identify the T. gondii replication partners loaded by the clamp","Complementation in yeast does not resolve native replisome composition"],"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2005,"claim":"Localization and knockout attempts tied TgPCNA1's molecular identity to cell biology by showing it is constitutively nuclear, forms S-phase replication foci, and is refractory to disruption, marking it as essential.","evidence":"TgPCNA1-GFP immunofluorescence across cell cycle stages and gene disruption attempts in tachyzoites","pmids":["15878790"],"confidence":"Medium","gaps":["Essentiality inferred from failure to disrupt, a negative genetic result","Mechanism of continuous nuclear retention unknown","Foci not mapped to specific replication origins"],"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":2025,"claim":"Quantitative live-cell imaging refined the spatiotemporal picture, showing TgPCNA1-marked replication initiates near centromeres with bell-shaped dynamics and validating it as an S-phase FUCCI reporter.","evidence":"TgPCNA1-NeonGreen live-cell imaging and immunofluorescence in the ToxoFUCCIS auxin-degron background","pmids":["40590555"],"confidence":"Medium","gaps":["Molecular basis of centromere-proximal replication initiation not defined","Does not identify clamp-loading or interacting factors"],"attribution":[{"species":"Toxoplasma gondii","strain":""}]},{"year":null,"claim":"The interactome, clamp-loading mechanism, and post-translational regulation that distinguish TgPCNA1 function and control its centromere-proximal replication dynamics remain undefined.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No replisomal or PIP-box partners identified","No structural model of the T. gondii clamp","Functional division of labor between TgPCNA1 and TgPCNA2 not mechanistically resolved"],"attribution":[{"species":"Toxoplasma gondii","strain":""}]}],"mechanism_profile":{"molecular_activity":[],"localization":[],"pathway":[],"complexes":[],"partners":[],"other_free_text":["TgPCNA1 is a ~40 kDa PCNA paralog arising from an ancestral apicomplexan gene duplication; shares 49% identity with PfPCNA1 [#0].","Essential in tachyzoites — gene could not be disrupted [#3].","Distinguished from the non-essential paralog TgPCNA2, which fails to complement yeast POL30 [#2].","Validated as an S-phase FUCCI reporter in the ToxoFUCCIS auxin-degron system [#4]."]},"strain_conflicts":[]},"prefetch_data":{},"corpus_meta":[{"pmid":"10960171","id":"PMC_10960171","title":"Two genes encoding unique proliferating-cell-nuclear-antigens are expressed in Toxoplasma gondii.","date":"2000","source":"Molecular and biochemical parasitology","url":"https://pubmed.ncbi.nlm.nih.gov/10960171","citation_count":21,"is_preprint":false},{"pmid":"15878790","id":"PMC_15878790","title":"Biochemical and genetic analysis of the distinct proliferating cell nuclear antigens of Toxoplasma gondii.","date":"2005","source":"Molecular and biochemical parasitology","url":"https://pubmed.ncbi.nlm.nih.gov/15878790","citation_count":20,"is_preprint":false},{"pmid":"40590555","id":"PMC_40590555","title":"Deciphering cell cycle organization of Toxoplasma endodyogeny.","date":"2025","source":"mBio","url":"https://pubmed.ncbi.nlm.nih.gov/40590555","citation_count":5,"is_preprint":false},{"pmid":"41607704","id":"PMC_41607704","title":"Assessing the Toxoplasma Tachyzoite Cell Cycle Phases Using Fluorescent Ubiquitination-Based Cell Cycle Indicator.","date":"2026","source":"Bio-protocol","url":"https://pubmed.ncbi.nlm.nih.gov/41607704","citation_count":0,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":4592,"output_tokens":1421,"usd":0.017545,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":6495,"output_tokens":2470,"usd":0.047113,"stage2_stop_reason":"end_turn"},"total_usd":0.064658,"stage1_batch_id":"msgbatch_01TEPNZ4MCzJ7xtsNwosiDRk","stage2_batch_id":"msgbatch_01FQShM7n1sfCr4pWTDShmki","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2000,\n      \"finding\": \"TgPCNA1 encodes a ~40 kDa protein expressed in T. gondii tachyzoites; two distinct PCNA genes (TgPCNA1 and TgPCNA2) exist in T. gondii genomic DNA, likely arising from gene duplication in the common ancestor of apicomplexans. TgPCNA1 and PfPCNA1 share 49% amino acid identity, higher than intraspecies PCNA pairs (27–30%).\",\n      \"method\": \"cDNA library screening, Southern blot, Northern blot, Western blot with specific antibodies, phylogenetic analysis\",\n      \"journal\": \"Molecular and biochemical parasitology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal methods (Southern, Northern, Western blot) in a single study establishing gene identity and protein expression, but no functional reconstitution or localization with functional consequence\",\n      \"pmids\": [\"10960171\"],\n      \"is_preprint\": false,\n      \"attribution\": [\n        {\"species\": \"Toxoplasma gondii\", \"strain\": \"Type I\"},\n        {\"species\": \"Toxoplasma gondii\", \"strain\": \"Type II\"},\n        {\"species\": \"Toxoplasma gondii\", \"strain\": \"Type III\"}\n      ]\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"TgPCNA1 is constitutively concentrated in the nucleus throughout all cell cycle phases in tachyzoites, including during S-phase where it displays a punctate pattern consistent with assembly into replication foci.\",\n      \"method\": \"Indirect immunofluorescence with TgPCNA1-GFP fusion protein and cell cycle staging\",\n      \"journal\": \"Molecular and biochemical parasitology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct live-cell and immunofluorescence localization across cell cycle phases, single lab\",\n      \"pmids\": [\"15878790\"],\n      \"is_preprint\": false,\n      \"attribution\": [\n        {\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}\n      ]\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Heterologous expression of TgPCNA1, but not TgPCNA2, complemented a POL30 (PCNA) cold-sensitive yeast mutant, indicating TgPCNA1 is functionally equivalent to canonical eukaryotic PCNA and likely serves as the major replisomal factor in T. gondii.\",\n      \"method\": \"Yeast complementation assay using cold-sensitive POL30 mutant strain\",\n      \"journal\": \"Molecular and biochemical parasitology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — functional complementation in a defined genetic background with a clear phenotypic readout; single lab but direct functional test\",\n      \"pmids\": [\"15878790\"],\n      \"is_preprint\": false,\n      \"attribution\": [\n        {\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}\n      ]\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"The TgPCNA1 gene could not be disrupted in tachyzoites, indicating it is essential for tachyzoite stage growth, consistent with its role as the primary replisomal PCNA.\",\n      \"method\": \"Gene disruption/knockout attempts in transgenic parasites\",\n      \"journal\": \"Molecular and biochemical parasitology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — failure to disrupt the gene is consistent with essentiality but relies on a negative genetic result in a single lab study\",\n      \"pmids\": [\"15878790\"],\n      \"is_preprint\": false,\n      \"attribution\": [\n        {\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}\n      ]\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"TgPCNA1 tagged with NeonGreen exhibits varied, dynamic subcellular localization across cell cycle phases, with DNA replication (detected by TgPCNA1 signal) initiating at or near centromeric regions and following a bell-shaped dynamic. TgPCNA1 was validated as a functional FUCCI probe for marking the S-phase in T. gondii tachyzoites.\",\n      \"method\": \"Quantitative live-cell imaging and immunofluorescence microscopy using TgPCNA1-NeonGreen in the auxin-induced degradation parental strain (ToxoFUCCIS system)\",\n      \"journal\": \"mBio\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct live-cell imaging with functional validation as a cell cycle marker, single lab with quantitative microscopy\",\n      \"pmids\": [\"40590555\"],\n      \"is_preprint\": false,\n      \"attribution\": [\n        {\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}\n      ]\n    }\n  ],\n  \"current_model\": \"TgPCNA1 is an essential, nuclear-localized proliferating cell nuclear antigen in Toxoplasma gondii tachyzoites that functions as the primary replisomal clamp (as demonstrated by yeast complementation), localizes constitutively in the nucleus with punctate replication foci during S-phase initiating near centromeres, and is distinguished from the non-essential TgPCNA2 paralog by its continuous nuclear presence throughout the cell cycle and its indispensability for tachyzoite growth.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"TgPCNA1 is the primary replisomal proliferating cell nuclear antigen of Toxoplasma gondii, functioning as the essential DNA replication clamp in the tachyzoite stage [#0, #2]. It is one of two PCNA paralogs (TgPCNA1 and TgPCNA2) that arose from an ancestral apicomplexan gene duplication [#0]. Heterologous expression of TgPCNA1, but not TgPCNA2, rescues a cold-sensitive yeast POL30 mutant, establishing it as the functional equivalent of canonical eukaryotic PCNA and the major replisomal factor [#2]. TgPCNA1 is constitutively nuclear across all cell cycle phases and reorganizes into punctate replication foci during S-phase, with DNA replication initiating at or near centromeric regions [#1, #4]. The gene cannot be disrupted in tachyzoites, indicating it is essential for growth [#3], and its S-phase-specific dynamics have been exploited to build it into a FUCCI cell cycle probe [#4]. Beyond its role as a replication clamp, the interacting partners and post-translational regulation of TgPCNA1 have not been characterized in the available corpus.\",\n  \"teleology\": [\n    {\n      \"year\": 2000,\n      \"claim\": \"Establishing that T. gondii carries two distinct PCNA genes defined the genetic architecture of the parasite's replication clamp machinery and raised the question of functional division between the paralogs.\",\n      \"evidence\": \"cDNA library screening with Southern, Northern, and Western blotting plus phylogenetic analysis of TgPCNA1/TgPCNA2 in tachyzoites\",\n      \"pmids\": [\"10960171\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Did not determine which paralog is the functional replisomal clamp\", \"No localization or essentiality data\", \"Roles of the two paralogs left undefined\"],\n      \"attribution\": [\n        {\"species\": \"Toxoplasma gondii\", \"strain\": \"Type I\"},\n        {\"species\": \"Toxoplasma gondii\", \"strain\": \"Type II\"},\n        {\"species\": \"Toxoplasma gondii\", \"strain\": \"Type III\"}\n      ]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Yeast complementation resolved which paralog is the canonical clamp by showing TgPCNA1, but not TgPCNA2, restores POL30 function, assigning TgPCNA1 the role of major replisomal PCNA.\",\n      \"evidence\": \"Complementation of a cold-sensitive POL30 yeast mutant with heterologously expressed TgPCNA1 vs TgPCNA2\",\n      \"pmids\": [\"15878790\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Does not identify the T. gondii replication partners loaded by the clamp\", \"Complementation in yeast does not resolve native replisome composition\"],\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Localization and knockout attempts tied TgPCNA1's molecular identity to cell biology by showing it is constitutively nuclear, forms S-phase replication foci, and is refractory to disruption, marking it as essential.\",\n      \"evidence\": \"TgPCNA1-GFP immunofluorescence across cell cycle stages and gene disruption attempts in tachyzoites\",\n      \"pmids\": [\"15878790\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Essentiality inferred from failure to disrupt, a negative genetic result\", \"Mechanism of continuous nuclear retention unknown\", \"Foci not mapped to specific replication origins\"],\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Quantitative live-cell imaging refined the spatiotemporal picture, showing TgPCNA1-marked replication initiates near centromeres with bell-shaped dynamics and validating it as an S-phase FUCCI reporter.\",\n      \"evidence\": \"TgPCNA1-NeonGreen live-cell imaging and immunofluorescence in the ToxoFUCCIS auxin-degron background\",\n      \"pmids\": [\"40590555\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Molecular basis of centromere-proximal replication initiation not defined\", \"Does not identify clamp-loading or interacting factors\"],\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"The interactome, clamp-loading mechanism, and post-translational regulation that distinguish TgPCNA1 function and control its centromere-proximal replication dynamics remain undefined.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No replisomal or PIP-box partners identified\", \"No structural model of the T. gondii clamp\", \"Functional division of labor between TgPCNA1 and TgPCNA2 not mechanistically resolved\"],\n      \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0043142\", \"supporting_discovery_ids\": [2], \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]},\n      {\"term_id\": \"GO:0030337\", \"supporting_discovery_ids\": [2, 1], \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [1, 4], \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]},\n      {\"term_id\": \"GO:0043596\", \"supporting_discovery_ids\": [1, 4], \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"GO:0006260\", \"supporting_discovery_ids\": [2, 4], \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]},\n      {\"term_id\": \"GO:0006261\", \"supporting_discovery_ids\": [1, 4], \"attribution\": [{\"species\": \"Toxoplasma gondii\", \"strain\": \"\"}]}\n    ],\n    \"complexes\": [],\n    \"partners\": [],\n    \"other_free_text\": [\n      \"TgPCNA1 is a ~40 kDa PCNA paralog arising from an ancestral apicomplexan gene duplication; shares 49% identity with PfPCNA1 [#0].\",\n      \"Essential in tachyzoites — gene could not be disrupted [#3].\",\n      \"Distinguished from the non-essential paralog TgPCNA2, which fails to complement yeast POL30 [#2].\",\n      \"Validated as an S-phase FUCCI reporter in the ToxoFUCCIS auxin-degron system [#4].\"\n    ]\n  },\n  \"strain_conflicts\": []\n}","audit_flag":null,"strains":[{"strain":"ME49","gene_id":"TGME49_247460","name":"PCNA1","product":"proliferating cell nuclear antigen PCNA1","uniprot_acc":"A0A125YTT1","chromosome":"TGME49_chrXII","start_pos":3353427},{"strain":"GT1","gene_id":"TGGT1_247460","name":null,"product":"proliferating cell nuclear antigen PCNA1","uniprot_acc":null,"chromosome":"TGGT1_chrXII","start_pos":3286520},{"strain":"RH88","gene_id":"TGRH88_061550","name":null,"product":"proliferating cell nuclear antigen PCNA1","uniprot_acc":null,"chromosome":"CM023093","start_pos":3407952},{"strain":"VEG","gene_id":"TGVEG_247460","name":null,"product":"proliferating cell nuclear antigen PCNA1","uniprot_acc":"B9PPR0","chromosome":"TGVEG_chrXII","start_pos":3325721}]}