{"gene":"DBF4B","run_date":"2026-06-09T22:57:19","timeline":{"discoveries":[{"year":2002,"finding":"DBF4B (Drf1/ASKL1) is a novel regulatory subunit of human CDC7 kinase: it binds CDC7 and activates its kinase activity, establishing that human CDC7 can be activated by alternative regulatory subunits analogous to cyclins activating CDKs.","method":"Co-immunoprecipitation, in vitro kinase assay","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 2 / Moderate — direct binding and kinase activation demonstrated by co-IP and in vitro kinase assay in a single focused study; independently replicated by multiple subsequent papers","pmids":["12065429"],"is_preprint":false},{"year":2005,"finding":"DBF4B (Drf1/ASKL1) binds and activates human CDC7, and the CDC7-ASKL1 complex phosphorylates MCM2. ASKL1 protein levels oscillate during the cell cycle, peaking at late S to G2/M phases, and the protein localizes predominantly to the nuclear-soluble (non-chromatin-bound) fraction.","method":"Co-immunoprecipitation, in vitro kinase assay, siRNA knockdown, cell-cycle synchronization, subcellular fractionation","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal methods (kinase assay, fractionation, siRNA) in a single focused study establishing substrate (MCM2), localization, and cell-cycle function","pmids":["15668232"],"is_preprint":false},{"year":2005,"finding":"In Xenopus egg extracts, Cdc7-Drf1 is far more abundant than Cdc7-Dbf4, and immunodepletion of Drf1 (but not Dbf4) severely inhibits Mcm4 phosphorylation and DNA replication, identifying Drf1 as the essential, developmentally regulated activator of Cdc7 in early vertebrate embryos. After gastrulation, Drf1 levels decline and Cdc7-Dbf4 becomes dominant.","method":"Immunodepletion from Xenopus egg extracts, in vitro kinase assay, DNA replication assay","journal":"Genes & development","confidence":"High","confidence_rationale":"Tier 2 / Strong — immunodepletion with functional rescue, replicated by at least two independent labs using Xenopus egg extracts","pmids":["16204181"],"is_preprint":false},{"year":2003,"finding":"Xenopus Drf1 forms an active complex with Cdc7. Under replication block (aphidicolin), Drf1 accumulates on chromatin in a checkpoint-dependent manner requiring ATR and Claspin; this accumulation is blocked by caffeine or depletion of ATR/Claspin. Drf1 promotes Cdc45 loading onto chromatin, and loss of Drf1 reduces Cdc45 chromatin association.","method":"Xenopus egg extract immunodepletion, chromatin binding assays, caffeine/ATR/Claspin depletion epistasis","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Moderate — genetic epistasis (depletion of ATR, Claspin) combined with chromatin fractionation showing Drf1's checkpoint-regulated chromatin accumulation and functional consequence on Cdc45 loading","pmids":["12897072"],"is_preprint":false},{"year":2006,"finding":"In Xenopus egg extracts, Cdc7/Drf1 complex is required for pre-replication complex (pre-RC) activation (but not assembly) and for DNA replication initiation. Cdc7/Drf1 chromatin binding is entirely dependent on pre-RC assembly, whereas Cdc7/Dbf4 chromatin binding has a pre-RC-independent step. Depletion of Cdc7/Drf1 inhibits DNA replication; depletion of Cdc7/Dbf4 has little effect in egg extracts.","method":"Immunodepletion from Xenopus egg extracts, chromatin binding assays, DNA replication assay","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — immunodepletion with functional readout (DNA replication), replicated across multiple independent labs using the same system","pmids":["16507577"],"is_preprint":false},{"year":2008,"finding":"Cdc7-Drf1 (DDK) complex formation, chromatin association, and kinase activity are NOT inhibited during DNA-damage-induced S-phase checkpoint in Xenopus egg extracts and mammalian cells. Instead, DDK (including Drf1-containing complexes) downregulates ATR-Chk1 checkpoint signaling; overexpression of the DDK regulatory subunit overrides replication inhibition caused by DNA-damaging agents, placing DDK as an upstream attenuator of the S-phase checkpoint.","method":"Xenopus egg extracts, kinase assays, overexpression in HeLa cells, checkpoint signaling assays","journal":"Molecular cell","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal methods (egg extracts + mammalian cells) but Drf1-specific contribution not fully separated from Dbf4 in all experiments","pmids":["19111665"],"is_preprint":false},{"year":2008,"finding":"The Cdc7-Drf1 kinase (DDK) exists in a stable complex with Scc2-Scc4 in Xenopus egg extracts. DDK is required to tether Scc2-Scc4 to pre-replication complexes on chromatin, thereby enabling cohesin loading; catalytically inactive DDK cannot rescue this function, demonstrating that DDK kinase activity is required for Scc2-Scc4 chromatin recruitment.","method":"Co-immunoprecipitation, immunodepletion from Xenopus egg extracts, chromatin binding assays, catalytic mutant rescue","journal":"Genes & development","confidence":"High","confidence_rationale":"Tier 1-2 / Moderate — stable complex demonstrated by co-IP, functional requirement shown by immunodepletion with catalytic-dead rescue, multiple orthogonal methods in one study","pmids":["18628396"],"is_preprint":false},{"year":2010,"finding":"DBF4B (Drf1)-dependent kinase (DDK) directly interacts with and phosphorylates Claspin in vitro. The interaction requires a conserved binding motif on Claspin (corresponding to the first repeat of the Chk1-binding domain), with Asp861 and Gln866 being essential. Claspin mutants unable to bind DDK associate with and activate Chk1 normally but support slower DNA replication, indicating that DDK-Claspin interaction mediates a checkpoint-independent role in DNA replication.","method":"In vitro kinase assay, direct in vitro binding assay, site-directed mutagenesis, Xenopus egg extract reconstitution","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro reconstitution of direct binding and phosphorylation, mutagenesis of critical residues, functional validation in egg extracts; single lab but multiple orthogonal methods","pmids":["20190277"],"is_preprint":false},{"year":2017,"finding":"In Xenopus laevis, developmental activation of Chk1 at the mid-blastula transition (MBT) triggers SCFβ-TRCP-dependent proteasomal degradation of Drf1, which is the primary mechanism by which Chk1 blocks cell-cycle progression in the early embryo. Loss of Drf1 is essential for cell-cycle elongation at the blastula-to-gastrula stage.","method":"Xenopus laevis embryo manipulation, Chk1 activation/inhibition, proteasome inhibitor experiments, genetic epistasis","journal":"Developmental cell","confidence":"High","confidence_rationale":"Tier 2 / Moderate — genetic epistasis (Chk1 activation → Drf1 degradation) with SCFβ-TRCP pathway placement and functional rescue, multiple orthogonal approaches in one focused study","pmids":["28697335"],"is_preprint":false},{"year":2017,"finding":"SRSF1 promotes inclusion of DBF4B exon 6 by directly binding DBF4B pre-mRNA; the full-length DBF4B isoform (DBF4B-FL containing exon 6) is required for cancer cell proliferation and genomic stability. Overexpression of DBF4B-FL rescues DNA damage and growth defects caused by SRSF1 knockdown, placing DBF4B-FL downstream of SRSF1 in a pathway controlling genomic integrity.","method":"siRNA knockdown, overexpression rescue, in vitro/in vivo tumorigenic assays, RNA-binding assay (SRSF1 binding to DBF4B pre-mRNA)","journal":"Cell reports","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — rescue experiment (DBF4B-FL overexpression) and knockdown phenotype provide pathway placement, but mechanistic detail of how DBF4B-FL maintains genomic stability is not fully resolved","pmids":["29262322"],"is_preprint":false},{"year":2024,"finding":"In human cells, DRF1 (DBF4B)-deficient cells generated by genome editing are viable but show signs of genomic instability, indicating DRF1 can independently support CDC7 for bulk DNA replication. However, CDC7 function at replication forks is entirely dependent on DBF4 and NOT on DRF1; DBF4-deficient cells show altered replication efficiency and partial deficiency in MCM helicase phosphorylation, whereas DRF1 loss does not affect these fork-associated functions.","method":"CRISPR/Cas9 genome editing to generate isogenic DBF4- or DRF1-deficient cell lines, DNA replication assays, MCM phosphorylation assays, replication timing analysis","journal":"The Journal of cell biology","confidence":"High","confidence_rationale":"Tier 2 / Moderate — isogenic genome-edited cell lines with multiple functional readouts; rigorous negative result (DRF1 not required at forks) from a focused mechanistic study","pmids":["38865090"],"is_preprint":false}],"current_model":"DBF4B (Drf1/ASKL1) is a vertebrate-specific, cell-cycle-regulated activating subunit of CDC7 kinase that promotes DNA replication initiation by binding CDC7, enabling phosphorylation of MCM substrates (MCM2, MCM4), and tethering the Scc2-Scc4 cohesin loader to pre-replication complexes; it is the dominant CDC7 activator in early vertebrate embryos and Xenopus egg extracts (where it is far more abundant than DBF4), its chromatin association is regulated by an ATR/Claspin-dependent intra-S checkpoint, and at the mid-blastula transition it is targeted for SCFβ-TRCP-dependent degradation downstream of Chk1, though in human somatic cells CDC7 activity at replication forks depends primarily on DBF4 rather than DBF4B."},"narrative":{"mechanistic_narrative":"DBF4B (Drf1/ASKL1) is a vertebrate cell-cycle-regulated activating subunit of the CDC7 kinase (DDK) that drives DNA replication initiation, functioning analogously to a cyclin in CDK activation [PMID:12065429]. It binds and activates human CDC7 to phosphorylate MCM-helicase substrates including MCM2 and MCM4, with its protein levels oscillating to peak in late S to G2/M and the protein residing predominantly in the nuclear-soluble fraction [PMID:15668232, PMID:16204181]. In early vertebrate embryos and Xenopus egg extracts, Cdc7-Drf1 is far more abundant than Cdc7-Dbf4 and is the essential activator of CDC7 for pre-replication-complex activation, Cdc45 loading, and replication initiation, while its chromatin recruitment is entirely dependent on pre-RC assembly [PMID:16204181, PMID:12897072, PMID:16507577]. Beyond initiation, DDK forms a stable complex with the cohesin loader Scc2-Scc4 and uses its kinase activity to tether Scc2-Scc4 to pre-replication complexes, coupling replication licensing to cohesin loading [PMID:18628396]. DDK also directly binds and phosphorylates Claspin through a conserved motif and acts as an upstream attenuator of the ATR-Chk1 S-phase checkpoint, supporting a checkpoint-independent role in replication [PMID:19111665, PMID:20190277]. At the mid-blastula transition, developmental Chk1 activation triggers SCFβ-TRCP-dependent degradation of Drf1 to elongate the cell cycle [PMID:28697335]. In human somatic cells the two activators are functionally separable: CDC7 activity at replication forks depends on DBF4 rather than DBF4B, although DBF4B can independently support bulk replication and its loss produces genomic instability [PMID:38865090]; a full-length DBF4B isoform generated by SRSF1-promoted exon-6 inclusion is required for cancer-cell proliferation and genomic stability [PMID:29262322].","teleology":[{"year":2002,"claim":"Established that human CDC7 is not activated by a single dedicated subunit but can be turned on by an alternative regulatory partner, defining DBF4B as a cyclin-like CDC7 activator.","evidence":"Co-immunoprecipitation and in vitro kinase assay of human CDC7-DBF4B","pmids":["12065429"],"confidence":"High","gaps":["No substrate identified in this study","Cell-cycle and developmental roles not yet addressed"]},{"year":2005,"claim":"Defined the substrate and cell-cycle behavior of human DBF4B, showing the CDC7-DBF4B complex phosphorylates MCM2 and that DBF4B oscillates and is largely non-chromatin-bound.","evidence":"Co-IP, in vitro kinase assay, siRNA, cell-cycle synchronization and subcellular fractionation in human cells","pmids":["15668232"],"confidence":"High","gaps":["Relative importance versus DBF4 not resolved","Chromatin-recruitment mechanism unclear given non-chromatin localization"]},{"year":2003,"claim":"Showed Drf1 chromatin accumulation is governed by an ATR/Claspin-dependent checkpoint and feeds into Cdc45 loading, linking the CDC7 activator to replication initiation control.","evidence":"Xenopus egg extract immunodepletion, chromatin binding, and caffeine/ATR/Claspin epistasis","pmids":["12897072"],"confidence":"High","gaps":["Direct kinase targets at Cdc45 loading step not defined","Does not establish Drf1 dominance over Dbf4"]},{"year":2005,"claim":"Identified Drf1 as the dominant, developmentally regulated CDC7 activator in early vertebrate embryos, where Dbf4 is dispensable for replication.","evidence":"Immunodepletion with functional MCM4 phosphorylation and DNA replication readouts in Xenopus egg extracts","pmids":["16204181"],"confidence":"High","gaps":["Mechanism of post-gastrulation Drf1 decline not defined here","Somatic-cell relevance untested"]},{"year":2006,"claim":"Distinguished the chromatin-loading requirements of the two activators, showing Cdc7/Drf1 binding is strictly pre-RC-dependent and required for pre-RC activation rather than assembly.","evidence":"Immunodepletion, chromatin binding and DNA replication assays in Xenopus egg extracts","pmids":["16507577"],"confidence":"High","gaps":["Molecular basis of the Dbf4 pre-RC-independent loading step unknown","Does not address fork-associated functions"]},{"year":2008,"claim":"Revealed an unexpected role for DDK as an upstream attenuator of the ATR-Chk1 S-phase checkpoint rather than a checkpoint target.","evidence":"Xenopus egg extracts, kinase assays, and DDK-subunit overexpression in HeLa checkpoint assays","pmids":["19111665"],"confidence":"Medium","gaps":["Drf1-specific contribution not fully separated from Dbf4","Direct checkpoint substrate of DDK not identified here"]},{"year":2008,"claim":"Connected DDK kinase activity to sister-chromatid cohesion by showing it stably binds and tethers the Scc2-Scc4 cohesin loader to pre-RCs.","evidence":"Co-IP, immunodepletion, chromatin binding and catalytic-dead rescue in Xenopus egg extracts","pmids":["18628396"],"confidence":"High","gaps":["Phosphorylation target mediating Scc2-Scc4 recruitment not defined","Human-cell confirmation absent"]},{"year":2010,"claim":"Provided a molecular basis for the DDK-checkpoint interface by mapping a direct DDK-Claspin interaction motif and separating a checkpoint-independent replication role.","evidence":"In vitro binding/kinase assays, site-directed mutagenesis (Asp861/Gln866) and egg extract reconstitution","pmids":["20190277"],"confidence":"High","gaps":["Functional Claspin phosphosites not mapped","In vivo consequence in somatic cells untested"]},{"year":2017,"claim":"Explained how the developmental cell-cycle slowdown is enforced: Chk1 directs SCFβ-TRCP-dependent degradation of Drf1 at the mid-blastula transition.","evidence":"Xenopus embryo manipulation, Chk1 activation/inhibition, proteasome inhibition and genetic epistasis","pmids":["28697335"],"confidence":"High","gaps":["Degron and direct E3 contact sites on Drf1 not defined","Whether somatic DBF4B is similarly regulated unknown"]},{"year":2017,"claim":"Linked DBF4B isoform choice to cancer cell biology, showing SRSF1-driven exon-6 inclusion produces a full-length DBF4B required for proliferation and genomic stability.","evidence":"siRNA knockdown, overexpression rescue, tumorigenic assays and SRSF1 RNA-binding assay","pmids":["29262322"],"confidence":"Medium","gaps":["Mechanism by which DBF4B-FL maintains genomic stability unresolved","Splice-variant difference in CDC7 activation not characterized"]},{"year":2024,"claim":"Resolved the division of labor between the two activators in human cells, showing CDC7 fork function depends on DBF4 while DBF4B can independently support bulk replication.","evidence":"Isogenic CRISPR/Cas9 DBF4- and DRF1-deficient cell lines with replication, MCM phosphorylation and replication-timing assays","pmids":["38865090"],"confidence":"High","gaps":["The non-fork replication functions DBF4B supports are not defined","Source of genomic instability in DRF1-deficient cells unclear"]},{"year":null,"claim":"How DBF4B-specific (versus DBF4) substrate selection, chromatin targeting, and genome-stability functions are determined in human somatic cells remains unresolved.","evidence":"","pmids":[],"confidence":"High","gaps":["DBF4B-specific substrates beyond MCM2 not defined in human cells","Structural basis for distinct DBF4 vs DBF4B fork dependence unknown","Disease relevance of DBF4B-FL isoform not mechanistically established"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[1,2,6,7]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[0,2]},{"term_id":"GO:0016740","term_label":"transferase activity","supporting_discovery_ids":[1,7]}],"localization":[{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[1]},{"term_id":"GO:0000228","term_label":"nuclear chromosome","supporting_discovery_ids":[3,4,6]}],"pathway":[{"term_id":"R-HSA-69306","term_label":"DNA Replication","supporting_discovery_ids":[2,3,4,10]},{"term_id":"R-HSA-1640170","term_label":"Cell Cycle","supporting_discovery_ids":[1,8]},{"term_id":"R-HSA-8953897","term_label":"Cellular responses to stimuli","supporting_discovery_ids":[3,5,7]}],"complexes":["CDC7-DBF4B (DDK)","DDK-Scc2-Scc4"],"partners":["CDC7","MCM2","MCM4","CDC45","SCC2","SCC4","CLASPIN","SRSF1"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q8NFT6","full_name":"Protein DBF4 homolog B","aliases":["Activator of S phase kinase-like protein 1","ASK-like protein 1","Chiffon homolog B","Dbf4-related factor 1"],"length_aa":615,"mass_kda":67.2,"function":"Regulatory subunit for CDC7 which activates its kinase activity thereby playing a central role in DNA replication and cell proliferation. Required for progression of S and M phases. The complex CDC7-DBF4B selectively phosphorylates MCM2 subunit at 'Ser-40' and then is involved in regulating the initiation of DNA replication during cell cycle","subcellular_location":"Nucleus","url":"https://www.uniprot.org/uniprotkb/Q8NFT6/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/DBF4B","classification":"Not Classified","n_dependent_lines":26,"n_total_lines":1208,"dependency_fraction":0.02152317880794702},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/DBF4B","total_profiled":1310},"omim":[{"mim_id":"611661","title":"DBF4 ZINC FINGER B; DBF4B","url":"https://www.omim.org/entry/611661"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Nucleoplasm","reliability":"Supported"},{"location":"Vesicles","reliability":"Additional"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in many","driving_tissues":[],"url":"https://www.proteinatlas.org/search/DBF4B"},"hgnc":{"alias_symbol":["FLJ13087","DRF1","ASKL1","chifb","ZDBF1B"],"prev_symbol":[]},"alphafold":{"accession":"Q8NFT6","domains":[{"cath_id":"3.40.50.10190","chopping":"48-101_170-198","consensus_level":"medium","plddt":89.7189,"start":48,"end":198},{"cath_id":"-","chopping":"298-332","consensus_level":"medium","plddt":94.9374,"start":298,"end":332}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q8NFT6","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q8NFT6-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q8NFT6-F1-predicted_aligned_error_v6.png","plddt_mean":54.84},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=DBF4B","jax_strain_url":"https://www.jax.org/strain/search?query=DBF4B"},"sequence":{"accession":"Q8NFT6","fasta_url":"https://rest.uniprot.org/uniprotkb/Q8NFT6.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q8NFT6/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q8NFT6"}},"corpus_meta":[{"pmid":"12676083","id":"PMC_12676083","title":"Disruption of the Diaphanous-related formin Drf1 gene encoding mDia1 reveals a role for Drf3 as an effector for Cdc42.","date":"2003","source":"Current biology : CB","url":"https://pubmed.ncbi.nlm.nih.gov/12676083","citation_count":205,"is_preprint":false},{"pmid":"18628396","id":"PMC_18628396","title":"Cdc7-Drf1 kinase links chromosome cohesion to the initiation of DNA replication in Xenopus egg extracts.","date":"2008","source":"Genes & development","url":"https://pubmed.ncbi.nlm.nih.gov/18628396","citation_count":99,"is_preprint":false},{"pmid":"17699759","id":"PMC_17699759","title":"Myeloproliferative defects following targeting of the Drf1 gene encoding the mammalian diaphanous related formin mDia1.","date":"2007","source":"Cancer research","url":"https://pubmed.ncbi.nlm.nih.gov/17699759","citation_count":71,"is_preprint":false},{"pmid":"12065429","id":"PMC_12065429","title":"Drf1, a novel regulatory subunit for human Cdc7 kinase.","date":"2002","source":"The EMBO journal","url":"https://pubmed.ncbi.nlm.nih.gov/12065429","citation_count":69,"is_preprint":false},{"pmid":"29262322","id":"PMC_29262322","title":"SRSF1 Prevents DNA Damage and Promotes Tumorigenesis through Regulation of DBF4B Pre-mRNA Splicing.","date":"2017","source":"Cell reports","url":"https://pubmed.ncbi.nlm.nih.gov/29262322","citation_count":63,"is_preprint":false},{"pmid":"15668232","id":"PMC_15668232","title":"A second human Dbf4/ASK-related protein, Drf1/ASKL1, is required for efficient progression of S and M phases.","date":"2005","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/15668232","citation_count":56,"is_preprint":false},{"pmid":"16204181","id":"PMC_16204181","title":"Cdc7-Drf1 is a developmentally regulated protein kinase required for the initiation of vertebrate DNA replication.","date":"2005","source":"Genes & development","url":"https://pubmed.ncbi.nlm.nih.gov/16204181","citation_count":56,"is_preprint":false},{"pmid":"19111665","id":"PMC_19111665","title":"The role of Dbf4/Drf1-dependent kinase Cdc7 in DNA-damage checkpoint control.","date":"2008","source":"Molecular cell","url":"https://pubmed.ncbi.nlm.nih.gov/19111665","citation_count":51,"is_preprint":false},{"pmid":"12897072","id":"PMC_12897072","title":"Xenopus Drf1, a regulator of Cdc7, displays checkpoint-dependent accumulation on chromatin during an S-phase arrest.","date":"2003","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/12897072","citation_count":48,"is_preprint":false},{"pmid":"28697335","id":"PMC_28697335","title":"Chk1 Inhibition of the Replication Factor Drf1 Guarantees Cell-Cycle Elongation at the Xenopus laevis Mid-blastula Transition.","date":"2017","source":"Developmental cell","url":"https://pubmed.ncbi.nlm.nih.gov/28697335","citation_count":34,"is_preprint":false},{"pmid":"16507577","id":"PMC_16507577","title":"Xenopus CDC7/DRF1 complex is required for the initiation of DNA replication.","date":"2006","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/16507577","citation_count":25,"is_preprint":false},{"pmid":"20190277","id":"PMC_20190277","title":"Drf1-dependent kinase interacts with Claspin through a conserved protein motif.","date":"2010","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/20190277","citation_count":5,"is_preprint":false},{"pmid":"38865090","id":"PMC_38865090","title":"DBF4, not DRF1, is the crucial regulator of CDC7 kinase at replication forks.","date":"2024","source":"The Journal of cell biology","url":"https://pubmed.ncbi.nlm.nih.gov/38865090","citation_count":2,"is_preprint":false},{"pmid":"30821612","id":"PMC_30821612","title":"Search for transcription factors affecting productivity of the polyketide FR901512 in filamentous fungal sp. No. 14919 and identification of Drf1, a novel negative regulator of the biosynthetic gene cluster.","date":"2019","source":"Bioscience, biotechnology, and biochemistry","url":"https://pubmed.ncbi.nlm.nih.gov/30821612","citation_count":2,"is_preprint":false},{"pmid":null,"id":"bio_10.1101_2024.09.19.24313988","title":"Molecular Characterization of Pediatric B-cell Acute Lymphoblastic Leukemia using Integrative Transcriptomics: A Multicenter Study in Argentina","date":"2024-09-22","source":"bioRxiv","url":"https://doi.org/10.1101/2024.09.19.24313988","citation_count":0,"is_preprint":true}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":8822,"output_tokens":3155,"usd":0.036895,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":10593,"output_tokens":3712,"usd":0.072883,"stage2_stop_reason":"end_turn"},"total_usd":0.109778,"stage1_batch_id":"msgbatch_01ACAxJQabDsht39JXeWG22d","stage2_batch_id":"msgbatch_01QEU22A9U5sbPTgsMzTmvSf","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2002,\n      \"finding\": \"DBF4B (Drf1/ASKL1) is a novel regulatory subunit of human CDC7 kinase: it binds CDC7 and activates its kinase activity, establishing that human CDC7 can be activated by alternative regulatory subunits analogous to cyclins activating CDKs.\",\n      \"method\": \"Co-immunoprecipitation, in vitro kinase assay\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct binding and kinase activation demonstrated by co-IP and in vitro kinase assay in a single focused study; independently replicated by multiple subsequent papers\",\n      \"pmids\": [\"12065429\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"DBF4B (Drf1/ASKL1) binds and activates human CDC7, and the CDC7-ASKL1 complex phosphorylates MCM2. ASKL1 protein levels oscillate during the cell cycle, peaking at late S to G2/M phases, and the protein localizes predominantly to the nuclear-soluble (non-chromatin-bound) fraction.\",\n      \"method\": \"Co-immunoprecipitation, in vitro kinase assay, siRNA knockdown, cell-cycle synchronization, subcellular fractionation\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal methods (kinase assay, fractionation, siRNA) in a single focused study establishing substrate (MCM2), localization, and cell-cycle function\",\n      \"pmids\": [\"15668232\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"In Xenopus egg extracts, Cdc7-Drf1 is far more abundant than Cdc7-Dbf4, and immunodepletion of Drf1 (but not Dbf4) severely inhibits Mcm4 phosphorylation and DNA replication, identifying Drf1 as the essential, developmentally regulated activator of Cdc7 in early vertebrate embryos. After gastrulation, Drf1 levels decline and Cdc7-Dbf4 becomes dominant.\",\n      \"method\": \"Immunodepletion from Xenopus egg extracts, in vitro kinase assay, DNA replication assay\",\n      \"journal\": \"Genes & development\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — immunodepletion with functional rescue, replicated by at least two independent labs using Xenopus egg extracts\",\n      \"pmids\": [\"16204181\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"Xenopus Drf1 forms an active complex with Cdc7. Under replication block (aphidicolin), Drf1 accumulates on chromatin in a checkpoint-dependent manner requiring ATR and Claspin; this accumulation is blocked by caffeine or depletion of ATR/Claspin. Drf1 promotes Cdc45 loading onto chromatin, and loss of Drf1 reduces Cdc45 chromatin association.\",\n      \"method\": \"Xenopus egg extract immunodepletion, chromatin binding assays, caffeine/ATR/Claspin depletion epistasis\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic epistasis (depletion of ATR, Claspin) combined with chromatin fractionation showing Drf1's checkpoint-regulated chromatin accumulation and functional consequence on Cdc45 loading\",\n      \"pmids\": [\"12897072\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"In Xenopus egg extracts, Cdc7/Drf1 complex is required for pre-replication complex (pre-RC) activation (but not assembly) and for DNA replication initiation. Cdc7/Drf1 chromatin binding is entirely dependent on pre-RC assembly, whereas Cdc7/Dbf4 chromatin binding has a pre-RC-independent step. Depletion of Cdc7/Drf1 inhibits DNA replication; depletion of Cdc7/Dbf4 has little effect in egg extracts.\",\n      \"method\": \"Immunodepletion from Xenopus egg extracts, chromatin binding assays, DNA replication assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — immunodepletion with functional readout (DNA replication), replicated across multiple independent labs using the same system\",\n      \"pmids\": [\"16507577\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Cdc7-Drf1 (DDK) complex formation, chromatin association, and kinase activity are NOT inhibited during DNA-damage-induced S-phase checkpoint in Xenopus egg extracts and mammalian cells. Instead, DDK (including Drf1-containing complexes) downregulates ATR-Chk1 checkpoint signaling; overexpression of the DDK regulatory subunit overrides replication inhibition caused by DNA-damaging agents, placing DDK as an upstream attenuator of the S-phase checkpoint.\",\n      \"method\": \"Xenopus egg extracts, kinase assays, overexpression in HeLa cells, checkpoint signaling assays\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal methods (egg extracts + mammalian cells) but Drf1-specific contribution not fully separated from Dbf4 in all experiments\",\n      \"pmids\": [\"19111665\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"The Cdc7-Drf1 kinase (DDK) exists in a stable complex with Scc2-Scc4 in Xenopus egg extracts. DDK is required to tether Scc2-Scc4 to pre-replication complexes on chromatin, thereby enabling cohesin loading; catalytically inactive DDK cannot rescue this function, demonstrating that DDK kinase activity is required for Scc2-Scc4 chromatin recruitment.\",\n      \"method\": \"Co-immunoprecipitation, immunodepletion from Xenopus egg extracts, chromatin binding assays, catalytic mutant rescue\",\n      \"journal\": \"Genes & development\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Moderate — stable complex demonstrated by co-IP, functional requirement shown by immunodepletion with catalytic-dead rescue, multiple orthogonal methods in one study\",\n      \"pmids\": [\"18628396\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"DBF4B (Drf1)-dependent kinase (DDK) directly interacts with and phosphorylates Claspin in vitro. The interaction requires a conserved binding motif on Claspin (corresponding to the first repeat of the Chk1-binding domain), with Asp861 and Gln866 being essential. Claspin mutants unable to bind DDK associate with and activate Chk1 normally but support slower DNA replication, indicating that DDK-Claspin interaction mediates a checkpoint-independent role in DNA replication.\",\n      \"method\": \"In vitro kinase assay, direct in vitro binding assay, site-directed mutagenesis, Xenopus egg extract reconstitution\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro reconstitution of direct binding and phosphorylation, mutagenesis of critical residues, functional validation in egg extracts; single lab but multiple orthogonal methods\",\n      \"pmids\": [\"20190277\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"In Xenopus laevis, developmental activation of Chk1 at the mid-blastula transition (MBT) triggers SCFβ-TRCP-dependent proteasomal degradation of Drf1, which is the primary mechanism by which Chk1 blocks cell-cycle progression in the early embryo. Loss of Drf1 is essential for cell-cycle elongation at the blastula-to-gastrula stage.\",\n      \"method\": \"Xenopus laevis embryo manipulation, Chk1 activation/inhibition, proteasome inhibitor experiments, genetic epistasis\",\n      \"journal\": \"Developmental cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic epistasis (Chk1 activation → Drf1 degradation) with SCFβ-TRCP pathway placement and functional rescue, multiple orthogonal approaches in one focused study\",\n      \"pmids\": [\"28697335\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"SRSF1 promotes inclusion of DBF4B exon 6 by directly binding DBF4B pre-mRNA; the full-length DBF4B isoform (DBF4B-FL containing exon 6) is required for cancer cell proliferation and genomic stability. Overexpression of DBF4B-FL rescues DNA damage and growth defects caused by SRSF1 knockdown, placing DBF4B-FL downstream of SRSF1 in a pathway controlling genomic integrity.\",\n      \"method\": \"siRNA knockdown, overexpression rescue, in vitro/in vivo tumorigenic assays, RNA-binding assay (SRSF1 binding to DBF4B pre-mRNA)\",\n      \"journal\": \"Cell reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — rescue experiment (DBF4B-FL overexpression) and knockdown phenotype provide pathway placement, but mechanistic detail of how DBF4B-FL maintains genomic stability is not fully resolved\",\n      \"pmids\": [\"29262322\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"In human cells, DRF1 (DBF4B)-deficient cells generated by genome editing are viable but show signs of genomic instability, indicating DRF1 can independently support CDC7 for bulk DNA replication. However, CDC7 function at replication forks is entirely dependent on DBF4 and NOT on DRF1; DBF4-deficient cells show altered replication efficiency and partial deficiency in MCM helicase phosphorylation, whereas DRF1 loss does not affect these fork-associated functions.\",\n      \"method\": \"CRISPR/Cas9 genome editing to generate isogenic DBF4- or DRF1-deficient cell lines, DNA replication assays, MCM phosphorylation assays, replication timing analysis\",\n      \"journal\": \"The Journal of cell biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — isogenic genome-edited cell lines with multiple functional readouts; rigorous negative result (DRF1 not required at forks) from a focused mechanistic study\",\n      \"pmids\": [\"38865090\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"DBF4B (Drf1/ASKL1) is a vertebrate-specific, cell-cycle-regulated activating subunit of CDC7 kinase that promotes DNA replication initiation by binding CDC7, enabling phosphorylation of MCM substrates (MCM2, MCM4), and tethering the Scc2-Scc4 cohesin loader to pre-replication complexes; it is the dominant CDC7 activator in early vertebrate embryos and Xenopus egg extracts (where it is far more abundant than DBF4), its chromatin association is regulated by an ATR/Claspin-dependent intra-S checkpoint, and at the mid-blastula transition it is targeted for SCFβ-TRCP-dependent degradation downstream of Chk1, though in human somatic cells CDC7 activity at replication forks depends primarily on DBF4 rather than DBF4B.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"DBF4B (Drf1/ASKL1) is a vertebrate cell-cycle-regulated activating subunit of the CDC7 kinase (DDK) that drives DNA replication initiation, functioning analogously to a cyclin in CDK activation [#0]. It binds and activates human CDC7 to phosphorylate MCM-helicase substrates including MCM2 and MCM4, with its protein levels oscillating to peak in late S to G2/M and the protein residing predominantly in the nuclear-soluble fraction [#1, #2]. In early vertebrate embryos and Xenopus egg extracts, Cdc7-Drf1 is far more abundant than Cdc7-Dbf4 and is the essential activator of CDC7 for pre-replication-complex activation, Cdc45 loading, and replication initiation, while its chromatin recruitment is entirely dependent on pre-RC assembly [#2, #3, #4]. Beyond initiation, DDK forms a stable complex with the cohesin loader Scc2-Scc4 and uses its kinase activity to tether Scc2-Scc4 to pre-replication complexes, coupling replication licensing to cohesin loading [#6]. DDK also directly binds and phosphorylates Claspin through a conserved motif and acts as an upstream attenuator of the ATR-Chk1 S-phase checkpoint, supporting a checkpoint-independent role in replication [#5, #7]. At the mid-blastula transition, developmental Chk1 activation triggers SCF\\u03b2-TRCP-dependent degradation of Drf1 to elongate the cell cycle [#8]. In human somatic cells the two activators are functionally separable: CDC7 activity at replication forks depends on DBF4 rather than DBF4B, although DBF4B can independently support bulk replication and its loss produces genomic instability [#10]; a full-length DBF4B isoform generated by SRSF1-promoted exon-6 inclusion is required for cancer-cell proliferation and genomic stability [#9].\",\n  \"teleology\": [\n    {\n      \"year\": 2002,\n      \"claim\": \"Established that human CDC7 is not activated by a single dedicated subunit but can be turned on by an alternative regulatory partner, defining DBF4B as a cyclin-like CDC7 activator.\",\n      \"evidence\": \"Co-immunoprecipitation and in vitro kinase assay of human CDC7-DBF4B\",\n      \"pmids\": [\"12065429\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No substrate identified in this study\", \"Cell-cycle and developmental roles not yet addressed\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Defined the substrate and cell-cycle behavior of human DBF4B, showing the CDC7-DBF4B complex phosphorylates MCM2 and that DBF4B oscillates and is largely non-chromatin-bound.\",\n      \"evidence\": \"Co-IP, in vitro kinase assay, siRNA, cell-cycle synchronization and subcellular fractionation in human cells\",\n      \"pmids\": [\"15668232\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Relative importance versus DBF4 not resolved\", \"Chromatin-recruitment mechanism unclear given non-chromatin localization\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Showed Drf1 chromatin accumulation is governed by an ATR/Claspin-dependent checkpoint and feeds into Cdc45 loading, linking the CDC7 activator to replication initiation control.\",\n      \"evidence\": \"Xenopus egg extract immunodepletion, chromatin binding, and caffeine/ATR/Claspin epistasis\",\n      \"pmids\": [\"12897072\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct kinase targets at Cdc45 loading step not defined\", \"Does not establish Drf1 dominance over Dbf4\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Identified Drf1 as the dominant, developmentally regulated CDC7 activator in early vertebrate embryos, where Dbf4 is dispensable for replication.\",\n      \"evidence\": \"Immunodepletion with functional MCM4 phosphorylation and DNA replication readouts in Xenopus egg extracts\",\n      \"pmids\": [\"16204181\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism of post-gastrulation Drf1 decline not defined here\", \"Somatic-cell relevance untested\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Distinguished the chromatin-loading requirements of the two activators, showing Cdc7/Drf1 binding is strictly pre-RC-dependent and required for pre-RC activation rather than assembly.\",\n      \"evidence\": \"Immunodepletion, chromatin binding and DNA replication assays in Xenopus egg extracts\",\n      \"pmids\": [\"16507577\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular basis of the Dbf4 pre-RC-independent loading step unknown\", \"Does not address fork-associated functions\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Revealed an unexpected role for DDK as an upstream attenuator of the ATR-Chk1 S-phase checkpoint rather than a checkpoint target.\",\n      \"evidence\": \"Xenopus egg extracts, kinase assays, and DDK-subunit overexpression in HeLa checkpoint assays\",\n      \"pmids\": [\"19111665\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Drf1-specific contribution not fully separated from Dbf4\", \"Direct checkpoint substrate of DDK not identified here\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Connected DDK kinase activity to sister-chromatid cohesion by showing it stably binds and tethers the Scc2-Scc4 cohesin loader to pre-RCs.\",\n      \"evidence\": \"Co-IP, immunodepletion, chromatin binding and catalytic-dead rescue in Xenopus egg extracts\",\n      \"pmids\": [\"18628396\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Phosphorylation target mediating Scc2-Scc4 recruitment not defined\", \"Human-cell confirmation absent\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Provided a molecular basis for the DDK-checkpoint interface by mapping a direct DDK-Claspin interaction motif and separating a checkpoint-independent replication role.\",\n      \"evidence\": \"In vitro binding/kinase assays, site-directed mutagenesis (Asp861/Gln866) and egg extract reconstitution\",\n      \"pmids\": [\"20190277\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Functional Claspin phosphosites not mapped\", \"In vivo consequence in somatic cells untested\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Explained how the developmental cell-cycle slowdown is enforced: Chk1 directs SCF\\u03b2-TRCP-dependent degradation of Drf1 at the mid-blastula transition.\",\n      \"evidence\": \"Xenopus embryo manipulation, Chk1 activation/inhibition, proteasome inhibition and genetic epistasis\",\n      \"pmids\": [\"28697335\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Degron and direct E3 contact sites on Drf1 not defined\", \"Whether somatic DBF4B is similarly regulated unknown\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Linked DBF4B isoform choice to cancer cell biology, showing SRSF1-driven exon-6 inclusion produces a full-length DBF4B required for proliferation and genomic stability.\",\n      \"evidence\": \"siRNA knockdown, overexpression rescue, tumorigenic assays and SRSF1 RNA-binding assay\",\n      \"pmids\": [\"29262322\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism by which DBF4B-FL maintains genomic stability unresolved\", \"Splice-variant difference in CDC7 activation not characterized\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Resolved the division of labor between the two activators in human cells, showing CDC7 fork function depends on DBF4 while DBF4B can independently support bulk replication.\",\n      \"evidence\": \"Isogenic CRISPR/Cas9 DBF4- and DRF1-deficient cell lines with replication, MCM phosphorylation and replication-timing assays\",\n      \"pmids\": [\"38865090\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"The non-fork replication functions DBF4B supports are not defined\", \"Source of genomic instability in DRF1-deficient cells unclear\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How DBF4B-specific (versus DBF4) substrate selection, chromatin targeting, and genome-stability functions are determined in human somatic cells remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\"DBF4B-specific substrates beyond MCM2 not defined in human cells\", \"Structural basis for distinct DBF4 vs DBF4B fork dependence unknown\", \"Disease relevance of DBF4B-FL isoform not mechanistically established\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [1, 2, 6, 7]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [0, 2]},\n      {\"term_id\": \"GO:0016740\", \"supporting_discovery_ids\": [1, 7]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [1]},\n      {\"term_id\": \"GO:0000228\", \"supporting_discovery_ids\": [3, 4, 6]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-69306\", \"supporting_discovery_ids\": [2, 3, 4, 10]},\n      {\"term_id\": \"R-HSA-1640170\", \"supporting_discovery_ids\": [1, 8]},\n      {\"term_id\": \"R-HSA-8953897\", \"supporting_discovery_ids\": [3, 5, 7]}\n    ],\n    \"complexes\": [\"CDC7-DBF4B (DDK)\", \"DDK-Scc2-Scc4\"],\n    \"partners\": [\"CDC7\", \"MCM2\", \"MCM4\", \"CDC45\", \"Scc2\", \"Scc4\", \"Claspin\", \"SRSF1\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":7,"faith_total":7,"faith_pct":100.0}}