{"uniprot":"P0CJ89","gene":"DUX4L6","name":"Double homeobox protein 4-like protein 6","organism":"Homo sapiens (Human)","status":"dark","length":424,"sequence":"MALPTPSDSTLPAEARGRGRRRRLVWTPSQSEALRACFERNPYPGIATRERLAQAIGIPEPRVQIWFQNERSRQLRQHRRESRPWPGRRGPPEGRRKRTAVTGSQTALLLRAFEKDRFPGIAAREELARETGLPESRIQIWFQNRRARHPGQGGRAPAQAGGLCSAAPGGGHPAPSWVAFAHTGAWGTGLPAPHVPCAPGALPQGAFVSQAARAAPALQPSQAAPAEGVSQPAPARGDFAYAAPAPPDGALSHPQAPRWPPHPGKSREDRDPQRDGLPGPCAVAQPGPAQAGPQGQGVLAPPTSQGSPWWGWGRGPQVAGAAWEPQAGAAPPPQPAPPDASASARQGQMQGIPAPSQALQEPAPWSALPCGLLLDELLASPEFLQQAQPLLETEAPGELEASEEAASLEAPLSEEEYRALLEEL","function_summary":"A nuclear transcriptional regulator that uses tandem homeodomain DNA-binding modules to recognize cis-regulatory elements and activate RNA polymerase II–dependent transcription. By assembling with transcriptional coactivators and basal machinery, it stimulates gene programs that restrain proliferation and cell-cycle entry and can engage apoptotic pathways. Its activity centers in the nucleoplasm with transient excursions near nuclear and cytoplasmic interfaces that support assembly, trafficking, and regulation of transcriptional complexes.","plain_language":"DUX4L6 has barely been studied. The model's best guess: A nuclear transcriptional regulator that uses tandem homeodomain DNA-binding modules to recognize cis-regulatory elements and activate RNA polymerase II–dependent transcription. By assembling with transcriptional coactivators and basal machinery, it stimulates gene programs that restrain proliferation and cell-cycle entry and can engage apoptotic pathways.","uniprot_summary":"Binds to DNA.","go_terms":{"molecular_function":[{"id":"GO:0005515","label":"protein binding"},{"id":"GO:0001228","label":"DNA-binding transcription activator activity, RNA polymerase II-specific"},{"id":"GO:0000978","label":"RNA polymerase II cis-regulatory region sequence-specific DNA binding"}],"biological_process":[{"id":"GO:0008285","label":"negative regulation of cell population proliferation"},{"id":"GO:0006915","label":"apoptotic process"},{"id":"GO:0070317","label":"negative regulation of G0 to G1 transition"},{"id":"GO:0045944","label":"positive regulation of transcription by RNA polymerase II"}],"cellular_component":[{"id":"GO:0005829","label":"cytosol"},{"id":"GO:0005654","label":"nucleoplasm"},{"id":"GO:0005794","label":"Golgi apparatus"},{"id":"GO:0031965","label":"nuclear membrane"},{"id":"GO:0005730","label":"nucleolus"}]},"interpro":[{"id":"IPR009057","name":"Homeodomain-like superfamily","type":"homologous_superfamily","start":14,"end":86},{"id":"IPR009057","name":"Homeodomain-like superfamily","type":"homologous_superfamily","start":87,"end":154},{"id":"IPR001356","name":"Homeodomain","type":"domain","start":17,"end":81},{"id":"IPR001356","name":"Homeodomain","type":"domain","start":92,"end":156},{"id":"IPR051306","name":"Homeobox domain-containing regulator","type":"family","start":17,"end":380},{"id":"IPR000047","name":"Helix-turn-helix motif","type":"conserved_site","start":123,"end":148}],"reasoning":"I begin with the InterPro architecture. Two homeobox signatures dominate the N-terminal half of the protein: IPR001356 (Homeodomain, residues 17–81) and a second homeodomain call IPR001356 (Homeodomain, residues 92–156). These are embedded within broader homeodomain-like scaffolds: IPR009057 (Homeodomain-like superfamily, residues 14–86) at the N-terminal region and IPR009057 (Homeodomain-like superfamily, residues 87–154) overlapping the second homeodomain. This tandem arrangement of homeodomains is reinforced by IPR051306 (Homeobox domain-containing regulator family, residues 17–380), which extends far beyond the DNA-binding cores and signals a transcriptional regulator scaffold rather than an enzyme. A conserved DNA-recognition element, IPR000047 (Helix-turn-helix motif, residues 123–148), sits within the second homeodomain and provides the canonical recognition helix that inserts into the major groove of DNA. The ordered layout—tandem homeodomains bracketed by homeodomain-like superfamily envelopes and capped by an HTH recognition module—creates a high-specificity, high-affinity DNA-binding platform that targets cis-regulatory elements and recruits transcriptional machinery.\n\nThis architecture causes sequence-specific DNA binding and transcriptional activation. The paired homeodomains and HTH motif directly support GO:0000978 RNA polymerase II cis-regulatory region sequence-specific DNA binding and GO:0001228 DNA-binding transcription activator activity, RNA polymerase II-specific. The extended family region (IPR051306) and the absence of catalytic motifs imply that transcriptional output is tuned through protein–protein interfaces, consistent with GO:0005515 protein binding. Together, these features define a transcription factor that binds enhancers and promoters and stimulates RNA polymerase II-dependent transcription.\n\nFrom this molecular function, the biological processes follow. By activating Pol II transcription (GO:0045944 positive regulation of transcription by RNA polymerase II), the factor can drive programs that restrain proliferation and cell cycle entry, explaining GO:0008285 negative regulation of cell population proliferation and GO:0070317 negative regulation of G0 to G1 transition. Such repression can be coupled to cell-fate pathways; transcriptional control of pro-death modules and checkpoint pathways rationalizes GO:0006915 apoptotic process. The tandem homeodomains often integrate developmental and stress-responsive cues; here, their regulatory reach provides a mechanistic basis for coupling transcriptional activation to growth suppression and apoptosis.\n\nCellular localization is dictated by the DNA-centric mechanism. The homeodomain architecture and transcriptional role place the protein in the nucleus, specifically the GO:0005654 nucleoplasm where chromatin-bound transcription occurs. Dynamic shuttling and assembly of transcriptional complexes can transiently expose the factor to the GO:0005829 cytosol and GO:0031965 nuclear membrane during nuclear import/export and periphery-associated regulation. Association with ribonucleoprotein assembly and surveillance pathways can account for detection in the GO:0005730 nucleolus, and trafficking or quality-control routes may explain occasional residence near the GO:0005794 Golgi apparatus. The dominant steady-state, however, is nuclear.\n\nMechanistically, the tandem homeodomains bind specific cis-regulatory sequences and recruit coactivators and the basal transcriptional apparatus to stimulate Pol II initiation and elongation. I hypothesize that the protein assembles with Mediator and TFIID at enhancer–promoter hubs, engages histone acetyltransferases to open chromatin, and interfaces with cell-cycle regulators to enforce G0/G1 restraint. Likely partners include Mediator subunits and coactivators (e.g., EP300/CBP), core Pol II factors (e.g., TFIID/TAFs), SWI/SNF chromatin remodelers, and cell-cycle gatekeepers such as RB1/E2F complexes. Through these assemblies, the factor activates transcriptional programs that suppress proliferation and can tip the balance toward apoptosis when necessary.","category":"dark","control_evaluation":null,"validation_plan":null,"structure":{"source":"AlphaFold DB","pdb":"/structures/AF-P0CJ89.pdb","alphafold":"https://alphafold.ebi.ac.uk/entry/P0CJ89"},"links":{"uniprot":"https://www.uniprot.org/uniprotkb/P0CJ89/entry","atlas":"/p/P0CJ89"},"provenance":{"model":"BioReason-Pro (ESM3 esm3-sm-open-v1)","source_list":"Pharos Tdark","note":"AI prediction, not experimentally verified"}}