BRWD3 is a nuclear protein containing eight WD repeats and tandem bromodomains that participates in regulation of RNA polymerase II transcription. Mammalian studies connect its WD-repeat region to DDB1 binding and recruitment of transcriptional machinery to active promoters during early adipogenesis. The bromodomains are consistent with chromatin recognition, while the physiological histone-mark preferences and effector repertoire of the human protein remain incompletely resolved. Depletion of human BRWD3 alters cell morphology, and loss-of-function variants cause X-linked intellectual disability frequently accompanied by macrocephaly. The single Drosophila family homolog regulates histone deposition and KDM5 abundance; the conservation of its particular ubiquitin-ligase substrates among human BRWD3, BRWD1, and PHIP remains uncertain.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0005634 nucleus | IBA GO_REF:0000033 | ACCEPT | Summary: BRWD3 has a conserved nuclear localization. Reason: Exact GO:0005634/PTN000417686/descendant set joins the cached PTHR16266 IBD. The existing family member table identifies human BRWD3 Q6RI45 within PTHR16266, with PHIP Q8WWQ0 and BRWD1 Q9NSI6 as separate related members. No target-specific loss or exclusion evidence is present in the examined source records. Retain the curator-inferred nuclear localization; this is not a new direct localization experiment. Propagation Review Root cause: NO FAILURE CORE Sources checked: PANTHER:PTN000417686 SUPPORTS TRANSFER Exact term and descendant-source set match cached PAINT IBD. Full tree/MSA and each descendant experiment were not independently re-evaluated. Supporting Evidence: GO_REF:0000033 |
| GO:0006357 regulation of transcription by RNA polymerase II | IBA GO_REF:0000033 | ACCEPT | Summary: BRWD3 participates in conserved regulation of RNA polymerase II transcription. Reason: Exact GO:0006357/PTN000417686 IBD uses the same recorded MGI source and PHIP accession as the seed. The transfer asserts inherited Pol II transcription regulation rather than a pairwise human-PHIP equivalence. There is no examined evidence of a BRWD3-specific loss; retaining this broad conserved function is appropriate. Separately inspected mammalian experiments in PMID:34161765 show BRWD3-dependent DDB1 recruitment and immediate-early transcription in mouse 3T3-L1 cells. This supports the conserved regulatory role, with the species and construct limits kept explicit rather than being presented as a direct human transcription assay. Propagation Review Root cause: NO FAILURE CORE Sources checked: PANTHER:PTN000417686 SUPPORTS TRANSFER Exact GO:0006357 IBD source set verified; no donor-count objection, no inferred donor PMID or independently resolved MGI symbol. |
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Download this section (compressed HTML)Q: Which histone modifications are recognized quantitatively by full-length human BRWD3 in nucleosomes, and how do these preferences differ from BRWD1 and PHIP?
Q: Does the DDB1 recruitment mechanism established in mouse preadipocytes operate at endogenous human BRWD3 target loci, including neural cells affected by BRWD3 loss?
Q: Which of the five annotated human protein products retain the same chromatin-recognition and effector-recruitment functions?
Experiment: Compare purified full-length human BRWD3 and domain variants on matched modified and unmodified nucleosomes, then test DDB1 recruitment and nascent transcription after endogenous BRWD3 depletion and rescue in a defined human cell type. Include BRWD1/PHIP and isoform controls.
Hypothesis: Human BRWD3 combines histone recognition with DDB1 recruitment in a context-dependent manner.
Type: Biochemical binding and cellular separation-of-function rescue
What is not known — curated, literature-grounded statements of the open unknowns (the inverse of core functions).
Gap: Whether human BRWD3, BRWD1, or PHIP conserves the fly BRWD3-dependent degradation of KDM5-family demethylases remains unresolved.
OPEN BIOLOGY RESIDUAL_SUBGAP
What is known: Fly BRWD3 associates with KDM5 and promotes its ubiquitylation and turnover in embryos/S2-cell experiments. The paper explicitly withholds a conclusion about conservation in human proteins.
What would resolve it: Test endogenous human BRWD3 loss and rescue separately from BRWD1/PHIP, measure individual KDM5-family protein turnover and ubiquitylation, and reconstitute any supported substrate-recruitment reaction with defined components.
Provenance (the field's own admissions):
Gap: The histone-recognition and effector-recruitment activities of human BRWD3 are not yet resolved separately from the related PHIP and BRWD1 proteins in the inspected biochemical evidence.
OPEN BIOLOGY RESIDUAL_SUBGAP
What is known: GO:0140566 histone reader activity requires bringing a protein together with a histone form; it does not require a particular quantitative affinity or a specific histone mark. The H3K4-binding claim summarized in PMID:37722046 draws on human PHIP and fly-module assays, while the target-specific human BRWD3 peptide-array signals in PMID:22464331 were not inspected. Mouse BRWD3-dependent DDB1 promoter recruitment supports a conserved chromatin-adaptor mechanism, but the examined data do not independently resolve histone engagement by human BRWD3. GO:1990756 ubiquitin-like ligase-substrate adaptor activity requires bridging a ligase and its substrate; the inspected human CUL4-recruitment experiments concern PHIP, and the BRWD3-specific mammalian DDB1 transcription mechanism is CUL4-independent. These are limits on the present assignment, not evidence that human BRWD3 lacks either activity.
What would resolve it: Resolve human BRWD3 constructs and endogenous rescue separately from PHIP/BRWD1; directly measure nucleosome recognition and recruitment of DDB1 or a defined ligase-substrate pair.
Provenance (the field's own admissions):
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