{"uniprot":"Q6VB84","gene":"FOXD4L3","name":"Forkhead box protein D4-like 3","organism":"Homo sapiens (Human)","status":"dark","length":417,"sequence":"MNLPRAERLRSTPQRSLRDSDGEDGKIDVLGEEEDEDEVEDEEEAASQQFLEQSLQPGLQVARWGGVALPREHIEGGGGPSDPSEFGTKFRAPPRSAAASEDARQPAKPPYSYIALITMAILQNPHKRLTLSGICAFISGRFPYYRRKFPAWQNSIRHNLSLNDCFVKIPREPGHPGKGNYWSLDPASQDMFDNGSFLRRRKRFKRHQLTPGAHLPHPFPLPAAHAALHNPRPGPLLGAPAPPQPVPGAYPNTAPGRRPYALLHPHPLRYLLLSAPVYAGAPKKAEGAALATPAPFPCCSPHLVLSLGRRARVWRRHREADASLSALRVLCKGSGERVQGLRRICPRPRGATATCSSDHQACCIPRPLPLCCKCPPPPLLGQFCSNSSSIRRRTAPTAALPPRARCWAGTCRPRRPC","function_summary":"A nuclear transcriptional regulator that uses a winged-helix DNA-binding core to anchor on chromatin and assemble regulatory complexes controlling RNA polymerase II output. By recruiting activating and repressing cofactors, it can both stimulate and dampen target gene transcription, thereby tuning developmental programs with roles in neuronal and myogenic pathways. Its mechanism centers on chromatin engagement via a forkhead fold, followed by multivalent interactions that switch between activation and repression depending on context.","plain_language":"FOXD4L3 has barely been studied. The model's best guess: A nuclear transcriptional regulator that uses a winged-helix DNA-binding core to anchor on chromatin and assemble regulatory complexes controlling RNA polymerase II output. By recruiting activating and repressing cofactors, it can both stimulate and dampen target gene transcription, thereby tuning developmental programs with roles in neuronal and myogenic pathways.","uniprot_summary":"Probable transcriptional regulator. May be involved in neural and myogenic development.","go_terms":{"molecular_function":[{"id":"GO:0005515","label":"protein binding"}],"biological_process":[{"id":"GO:0045944","label":"positive regulation of transcription by RNA polymerase II"},{"id":"GO:0000122","label":"negative regulation of transcription by RNA polymerase II"},{"id":"GO:0006366","label":"transcription by RNA polymerase II"}],"cellular_component":[{"id":"GO:0005634","label":"nucleus"}]},"interpro":[{"id":"IPR036388","name":"Winged helix-like DNA-binding domain superfamily","type":"homologous_superfamily","start":96,"end":203},{"id":"IPR036390","name":"Winged helix DNA-binding domain superfamily","type":"homologous_superfamily","start":107,"end":202},{"id":"IPR001766","name":"Fork head domain","type":"domain","start":106,"end":202},{"id":"IPR050211","name":"Forkhead box domain-containing protein","type":"family","start":49,"end":265},{"id":"IPR018122","name":"Fork head domain conserved site1","type":"conserved_site","start":108,"end":121},{"id":"IPR030456","name":"Fork head domain conserved site 2","type":"conserved_site","start":152,"end":158}],"reasoning":"I begin with the InterPro architecture. The core is a canonical winged-helix DNA-binding module: IPR001766 (Fork head domain, residues 106–202) sits centrally and is flanked by two overlapping superfamily signatures—IPR036388 (Winged helix-like DNA-binding domain superfamily, residues 96–203) and IPR036390 (Winged helix DNA-binding domain superfamily, residues 107–202)—which together define a helix-turn-helix fold that grips DNA via a recognition helix and β-strand “wings.” Two conserved motifs within this domain, IPR018122 (Fork head domain conserved site1, residues 108–121) and IPR030456 (Fork head domain conserved site 2, residues 152–158), mark residues that stabilize DNA contact and fold assembly. The broader family envelope IPR050211 (Forkhead box domain-containing protein, residues 49–265) extends N- and C-terminally beyond the core, indicating regulatory regions that tune transcriptional output. This ordered layout—an N-terminal regulatory segment feeding into a tightly conserved winged-helix DNA-binding core—causes sequence-specific chromatin engagement and assembly of transcriptional complexes.\n\nFrom this architecture, the molecular function resolves as a DNA-anchored regulator that operates primarily through multivalent protein binding. The winged-helix domain provides the physical basis for chromatin association, while the flanking family region supplies interaction surfaces for cofactors; this supports GO:0005515 protein binding as the operative molecular function at the single-protein level.\n\nAnchoring to DNA enables bidirectional transcriptional control. The same DNA-binding scaffold can recruit co-activators or co-repressors, explaining participation in both GO:0045944 positive regulation of transcription by RNA polymerase II and GO:0000122 negative regulation of transcription by RNA polymerase II. Its direct role in assembling and stabilizing pre-initiation and elongation assemblies places it within GO:0006366 transcription by RNA polymerase II. Developmentally, a forkhead transcriptional regulator that toggles activation and repression naturally modulates lineage programs; coupling this with its nuclear action yields a coherent model for controlling neuronal and myogenic gene networks.\n\nCellular location follows directly. A winged-helix transcriptional regulator with extended regulatory termini functions where chromatin resides—hence GO:0005634 nucleus. The absence of transmembrane segments and the presence of nuclear DNA-binding machinery reinforce a soluble nuclear residency.\n\nMechanistically, I hypothesize that the protein binds forkhead motifs at target enhancers and promoters, then recruits chromatin-modifying and transcriptional machinery to either open chromatin and stimulate Pol II or compact chromatin and dampen transcription. Likely partners include Mediator and TFIID for activation; histone acetyltransferases (e.g., EP300/CBP) and SWI/SNF remodelers for activation; and HDAC complexes and NCoR/SMRT for repression. In neural and myogenic contexts, it may cooperate with lineage-defining transcription factors to fine-tune gene-expression thresholds.","category":"dark","control_evaluation":null,"validation_plan":null,"structure":{"source":"AlphaFold DB","pdb":"/structures/AF-Q6VB84.pdb","alphafold":"https://alphafold.ebi.ac.uk/entry/Q6VB84"},"links":{"uniprot":"https://www.uniprot.org/uniprotkb/Q6VB84/entry","atlas":"/p/Q6VB84"},"provenance":{"model":"BioReason-Pro (ESM3 esm3-sm-open-v1)","source_list":"Pharos Tdark","note":"AI prediction, not experimentally verified"}}