Affinage

ORC4

Origin recognition complex subunit 4 · UniProt O43929

Length
436 aa
Mass
50.4 kDa
Annotated
2026-06-10
19 papers in source corpus 17 papers cited in narrative 17 extracted findings
Cross-family judge vs UniProt: Affinage preferred faithfulness: 7/7 claims corpus-supported (100%)

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

ORC4 is a core subunit of the six-member origin recognition complex (ORC) that licenses DNA replication, co-purifying with ORC1, ORC2, and ORC5 in an intact six-subunit complex whose subunits share a common evolutionary origin with ORC1 and Cdc6 (PMID:9829972). It carries a C-terminal AAA+ ATPase module, and within this domain a hydrophobic IL(4) motif in the initiator-specific motif (ISM) mediates contacts with neighboring subunits ORC1, ORC2, and ORC5 and is also the docking site for Hsp70/DnaK chaperones; mutation of this motif disrupts the ORC4–ORC2 interaction and causes lethal or thermosensitive replication-defective phenotypes (PMID:20732327, PMID:17107343). ORC4 is the subunit that confers site-specific origin recognition: it binds tightly and specifically to AT-rich clusters at replication origins, and its presence is required for the rest of the complex to bind origin DNA strongly (PMID:11689699). Human ORC4 additionally recognizes non-canonical DNA, preferring triplex over duplex or single-stranded DNA and promoting T·A·T triplex formation in an ATP-binding-dependent manner, directing ORC toward origin sequences prone to adopting such structures (PMID:18652488, PMID:19690980). Beyond replication licensing, ORC4 has a distinct structural role in chromatin elimination: it oligomerizes into a cage-like sphere surrounding the chromosomes destined for elimination during murine polar body extrusion and during erythroid enucleation, and this activity is required for both processes (PMID:25502171, PMID:28230328, PMID:32972244). Conditional deletion of Orc4 in mouse oogenesis confirms its dual requirement, severely impairing polar body extrusion and abolishing zygotic DNA synthesis (PMID:34977916). Germline mutations in ORC4 cause Meier-Gorlin syndrome, an autosomal recessive disorder of growth and skeletal development, with the pathogenicity of disease alleles validated in yeast and metazoan models (PMID:21358631, PMID:31818869).

Mechanistic history

Synthesis pass · year-by-year structured walk · 9 steps
  1. 1998 High

    Established that ORC4 is a bona fide subunit of an intact, evolutionarily conserved six-member origin recognition complex rather than a loosely associated factor.

    Evidence Single-step immunoaffinity purification of ORC from Xenopus egg extract with protein microsequencing and human cDNA cloning

    PMID:9829972

    Open questions at the time
    • Did not define which subunit interfaces ORC4 occupies
    • No structural model of the assembled complex
  2. 2001 High

    Defined ORC4 as the subunit conferring site-specific origin recognition, answering how the complex achieves sequence specificity at replication origins.

    Evidence Reconstitution of purified S. pombe Orc proteins individually and in combination with DNA binding and cell-cycle chromatin fractionation

    PMID:11689699

    Open questions at the time
    • Mechanism shown in fission yeast via AT-hook motifs absent from human ORC4
    • Did not establish how human ORC4 lacking AT-hooks achieves specificity
  3. 2010 High

    Mapped the molecular interface ORC4 uses to contact partner subunits and chaperones, linking subunit assembly to a specific structural motif and viability.

    Evidence 3D electron microscopy of an Orc4p–DnaK complex with site-directed mutagenesis and allelic substitution in yeast

    PMID:20732327

    Open questions at the time
    • Demonstrated in S. cerevisiae; ISM interactions not directly mapped in human ORC4
    • Functional consequence of Hsp70 contacts for ORC assembly in vivo not fully resolved
  4. 2009 Medium

    Showed human ORC4 directly recognizes non-canonical DNA structures, addressing how metazoan origins lacking defined consensus sequences are selected.

    Evidence In vitro DNA binding assays with purified human ORC4 on triplex, duplex, and single-stranded substrates, plus ATP-binding mutant analysis of triplex formation

    PMID:18652488 PMID:19690980

    Open questions at the time
    • Triplex/duplex preference shown in vitro; physiological relevance at chromosomal origins not demonstrated
    • No genome-wide map of ORC4-bound non-canonical structures in human cells
  5. 2011 High

    Connected ORC4's replication function to human disease by identifying causative germline mutations, establishing clinical importance.

    Evidence Marker-assisted mapping, coding exon sequencing across families, and yeast functional complementation of the equivalent missense mutation

    PMID:21358631

    Open questions at the time
    • Tissue-specificity of the growth/skeletal phenotype from a ubiquitous replication factor unexplained
    • Validation relied on yeast surrogate rather than human cells
  6. 2019 High

    Demonstrated that the Meier-Gorlin allele acts through impaired DNA replication in a metazoan, settling the mechanistic basis of the disease phenotype.

    Evidence CRISPR/Cas9 knock-in of the MGS mutation at the endogenous Drosophila Orc4 locus with genetic epistasis and BrdU/DNA-content readouts

    PMID:31818869

    Open questions at the time
    • Tissue-specific basis of replication defect not fully resolved
    • Did not test the non-replicative chromatin-elimination role
  7. 2017 Medium

    Revealed a replication-independent structural role for ORC4: oligomerization into a cage around chromosomes destined for elimination, required for polar body extrusion.

    Evidence Immunolocalization across meiotic stages plus peptide-mediated blockade of ORC4 protein-protein interactions and forced pseudo-polar body extrusion in mouse oocytes

    PMID:25502171 PMID:28230328

    Open questions at the time
    • Molecular architecture of the ORC4 cage unknown
    • Whether other ORC subunits or chaperones participate not established
  8. 2020 Medium

    Generalized the chromatin-elimination role beyond meiosis by showing ORC4 is required for erythroid enucleation, indicating a conserved cage function.

    Evidence Immunofluorescence and siRNA knockdown with enucleation phenotype in Vacuolin-1-induced MEL cells

    PMID:32972244

    Open questions at the time
    • Single knockdown method without rescue
    • Mechanism of cage assembly during enucleation undefined
  9. 2022 High

    Provided definitive in vivo genetic confirmation that ORC4 is independently required for both polar body extrusion and zygotic DNA replication.

    Evidence ZP3-Cre conditional knockout of Orc4 exon 7 in mice with BrdU incorporation and oocyte maturation readouts

    PMID:34977916

    Open questions at the time
    • Does not separate the structural cage function from the replication function molecularly
    • Whether the two roles use the same or distinct ORC4 domains unresolved

Open questions

Synthesis pass · forward-looking unresolved questions
  • How a single subunit physically partitions between licensing replication within the hexameric ORC and forming an oligomeric cage during chromatin elimination remains mechanistically undefined.
  • No structure of the ORC4 chromatin-elimination cage
  • Domain requirements distinguishing replication versus cage roles not mapped
  • Human cage function shown only by analogy from mouse and MEL cells

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0003677 DNA binding 4 GO:0005198 structural molecule activity 3 GO:0140657 ATP-dependent activity 1
Localization
GO:0005694 chromosome 3 GO:0005634 nucleus 2
Pathway
R-HSA-69306 DNA Replication 3 R-HSA-1643685 Disease 2 R-HSA-1640170 Cell Cycle 1
Partners
HSP70/DNAKORC1ORC2ORC3ORC5ORC6
Complex memberships
origin recognition complex (ORC)

Evidence

Reading pass · 17 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
1997 Human ORC4 (HsORC4) is a 45-kDa subunit of the human origin recognition complex containing a putative nucleotide triphosphate binding motif; it is co-immunoprecipitated with HsORC2 from cell extracts, placing it as a component of the human ORC. Co-immunoprecipitation from human cell extracts; cDNA cloning and sequence analysis The Journal of biological chemistry Medium 9353276
1998 Human ORC4 protein (43-kDa subunit) co-purifies with Xenopus and human ORC (Orc1p, Orc2p, Orc5p, and other subunits) in a six-subunit complex; sequence analysis reveals ORC4 is structurally related to ORC1 and Cdc6p, suggesting a shared evolutionary origin among ORC subunits. Single-step immunoaffinity purification of ORC from Xenopus egg extract; protein microsequencing; cDNA cloning of human ORC4 The Journal of biological chemistry High 9829972
1999 The S. pombe Orc4p homologue (Orp4p) contains nine AT-hook motifs in its N-terminal domain that mediate binding to the minor groove of AT-tracts in the S. pombe replication origin ars1; the C-terminal domain shares homology with human/frog/yeast Orc4 proteins including conserved ATP-binding motifs. DNA binding assays with purified Orp4p and isolated N-terminal domain; sequence analysis of AT-hook motifs Proceedings of the National Academy of Sciences of the United States of America Medium 10077566
2001 In S. pombe, Orc4p alone binds tightly and specifically to clusters of A or T residues within replication origins required for origin activity; a complex of Orc1/2/3/5/6 (ORC-5) binds weakly and non-specifically to DNA alone, but strong ORC-5 binding requires presence of Orc4p, demonstrating that Orc4p determines site-specific ORC binding to replication origins. DNA binding assays with purified S. pombe Orc proteins reconstituted individually and in combination; chromatin fractionation across cell cycle phases Molecular and cellular biology High 11689699
2001 The C-terminal AAA+ domain of S. cerevisiae Orc4p shares structural elements (winged-helix domain, leucine-zipper dimerization motif) with bacterial replication initiator RepA; ScOrc4p interacts with Hsp70 family chaperones (DnaK in E. coli; Ssa/Ssb in yeast) both in vitro and in vivo, suggesting chaperones regulate ORC assembly. Sequence similarity analysis; biochemical and spectroscopic characterization; co-immunoprecipitation of Orc4p with Hsp70 chaperones in vitro and in vivo Proceedings of the National Academy of Sciences of the United States of America Medium 11296251
2007 S. cerevisiae Orc4p interacts preferentially with Orc5p via its C-terminal region (interacting with the N-terminal region of Orc5p); ATP binding to Orc5p (Walker A motif) is required for efficient interaction with Orc4p; over-production of Orc4p suppresses proteasome-mediated degradation of ORC caused by an Orc5p Walker A mutation. Yeast two-hybrid analysis; co-immunoprecipitation; proteasome inhibitor experiments; genetic suppression assays The Biochemical journal Medium 17107343
2008 Human ORC4 stimulates formation of inter- and intramolecular T·A·T DNA triplexes and novel homoadenine duplexes held together by Hoogsteen hydrogen bonds; this activity requires ATP binding by ORC4, as an ATP-binding mutant was inactive. In vitro DNA binding and structure formation assays with purified human ORC4; 7-deaza-dAMP substrate characterization; thermal stability measurements; ATP-binding mutant analysis Biochemistry Medium 18652488
2009 Human ORC4 binds DNA in a manner dependent on DNA length and structure, preferring triplex DNA over duplex or single-stranded DNA; this binding preference may direct ORC to origin sequences prone to adopting non-canonical structures. In vitro DNA binding assays with purified HsOrc4 on triplex, duplex, and ssDNA substrates of varying lengths Molecular biology reports Medium 19690980
2010 In S. cerevisiae Orc4p, a hydrophobic IL(4) sequence within the initiator specific motif (ISM) of the AAA+ domain is the primary binding target for DnaK/Hsp70 chaperones; mutation of IL(4) selectively disrupts Orc4p interaction with Orc2p; allelic substitution of individual IL(4) residues causes lethal (I184A) or thermosensitive (L185A, L186A) replication-defective phenotypes; Orc4p also interacts with Orc1p and Orc5p. 3D electron microscopy reconstruction of Orc4p–DnaK complex; pairwise co-expression in E. coli; site-directed mutagenesis; allelic substitution in yeast; in vivo and in vitro binding assays Journal of molecular biology High 20732327
2011 Germline mutations in ORC4 cause Meier-Gorlin syndrome (autosomal recessive; hallmarks: small stature, small ears, absent/small patellae); the equivalent yeast missense mutation was shown to be pathogenic in functional assays of cell growth, linking ORC4's replication function to the disease phenotype. Marker-assisted mapping; coding exon sequencing; yeast functional complementation assay Nature genetics High 21358631
2015 Human ORC4 binds topologically closed ori-β DHFR origin DNA and reversibly modifies its non-canonical bubble-like structure within the AT-rich region, using the energy of supercoiled DNA, suggesting ORC4 actively remodels DNA structure at replication origins. In vitro plasmid binding and topology assays with purified HsOrc4 on ori-β DHFR plasmid Cellular & molecular biology letters Low 26124052
2015 During murine female meiosis, ORC4 (but not ORC1, 3, 5, or 6) forms a sphere-like structure surrounding the chromosomes destined for polar body extrusion in both meiotic divisions; in zygotic G1, ORC4 is restricted to polar body nuclei and absent from pronuclei, transitioning to chromosomes at zygotic anaphase. Immunofluorescence microscopy of mouse oocytes and zygotes at defined meiotic and mitotic stages Journal of cellular biochemistry Medium 25502171
2017 ORC4 oligomerization is required to form the ORC4 cage around polar body chromosomes and is necessary for polar body extrusion (PBE) in murine oogenesis; peptides blocking ORC4 protein-protein interactions prevented cage formation and inhibited PBE, resulting in retention of two pronuclei in the oocyte. Additionally, forced extrusion of sperm chromatin as a pseudo-polar body resulted in that chromatin becoming enclosed in an ORC4 cage. Peptide injection into metaphase II oocytes; live imaging; immunofluorescence; forced pseudo-polar body extrusion assay Journal of cellular biochemistry Medium 28230328
2019 A Drosophila model carrying the Meier-Gorlin syndrome Orc4 mutation (engineered at the endogenous locus by Cas9) shows tissue-specific DNA replication defects and female sterility; genetic analysis classifies the allele as a hypomorph, and phenotypic analyses support disrupted DNA replication as the underlying cause of tissue-specific developmental defects. CRISPR/Cas9 knock-in of MGS mutation at endogenous Orc4 locus; genetic analysis; BrdU incorporation/DNA content analysis Genetics High 31818869
2020 ORC4 surrounds nuclei of MEL cells undergoing Vacuolin-1-induced enucleation, and siRNA-mediated knockdown of ORC4 prevents MEL cell enucleation, demonstrating a functional role for ORC4 in chromatin elimination analogous to its role in polar body extrusion. Immunofluorescence of MEL cells during enucleation; siRNA knockdown with enucleation phenotype readout Systems biology in reproductive medicine Medium 32972244
2021 In Candida albicans, Orc4 is constitutively localized to all centromeres genome-wide and is required for cell viability and CENPA stability; Orc4-bound early-replicating regions interact preferentially with each other in nuclear space, and Orc4, together with the helicase Mcm2 and CENPA chaperone Scm3, maintains centromeric chromatin stability and CENPA recruitment during late anaphase/telophase. Genome-wide ChIP-seq of Orc4; Hi-C; replication timing analysis; conditional depletion with viability and CENPA immunofluorescence readout; polymer chromosome modeling Genome research Medium 33514624
2022 Conditional deletion of Orc4 (exon 7) during oogenesis severely reduces polar body extrusion (~48% of oocytes arrested before anaphase I, only 25% forming normal first polar bodies) and abolishes zygotic DNA synthesis (Orc4-depleted MII oocytes arrested at two-cell stage without DNA synthesis), confirming ORC4 is required for both polar body extrusion and zygotic DNA replication. ZP3-Cre conditional knockout of Orc4 exon 7 in mice; BrdU incorporation; immunofluorescence; in vitro oocyte maturation assays Biology of reproduction High 34977916

Source papers

Stage 0 corpus · 19 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
1999 The fission yeast homologue of Orc4p binds to replication origin DNA via multiple AT-hooks. Proceedings of the National Academy of Sciences of the United States of America 182 10077566
2011 Mutations in origin recognition complex gene ORC4 cause Meier-Gorlin syndrome. Nature genetics 140 21358631
2001 Site-specific DNA binding of the Schizosaccharomyces pombe origin recognition complex is determined by the Orc4 subunit. Molecular and cellular biology 86 11689699
1998 The Orc4p and Orc5p subunits of the Xenopus and human origin recognition complex are related to Orc1p and Cdc6p. The Journal of biological chemistry 83 9829972
1997 Identification of HsORC4, a member of the human origin of replication recognition complex. The Journal of biological chemistry 68 9353276
2001 Similarities between the DNA replication initiators of Gram-negative bacteria plasmids (RepA) and eukaryotes (Orc4p)/archaea (Cdc6p). Proceedings of the National Academy of Sciences of the United States of America 31 11296251
2005 Spotted-dick, a zinc-finger protein of Drosophila required for expression of Orc4 and S phase. The EMBO journal 17 16369566
2009 Novel ORC4L gene mutation in B-cell lymphoproliferative disorders. The American journal of the medical sciences 13 20010161
2015 ORC4 surrounds extruded chromatin in female meiosis. Journal of cellular biochemistry 12 25502171
2010 Structural analysis of the interactions between hsp70 chaperones and the yeast DNA replication protein Orc4p. Journal of molecular biology 11 20732327
2009 Human initiation protein Orc4 prefers triple stranded DNA. Molecular biology reports 11 19690980
2021 Orc4 spatiotemporally stabilizes centromeric chromatin. Genome research 9 33514624
2019 Tissue-Specific DNA Replication Defects in Drosophila melanogaster Caused by a Meier-Gorlin Syndrome Mutation in Orc4. Genetics 6 31818869
2007 Mechanism for the degradation of origin recognition complex containing Orc5p with a defective Walker A motif and its suppression by over-production of Orc4p in yeast cells. The Biochemical journal 6 17107343
2022 Deletion of Orc4 during oogenesis severely reduces polar body extrusion and blocks zygotic DNA replication†. Biology of reproduction 5 34977916
2017 Higher Order Oligomerization of the Licensing ORC4 Protein Is Required for Polar Body Extrusion in Murine Meiosis. Journal of cellular biochemistry 5 28230328
2020 The role of ORC4 in enucleation of Murine Erythroleukemia (MEL) cells is similar to that in oocyte polar body extrusion. Systems biology in reproductive medicine 4 32972244
2008 Formation of noncanonical DNA structures mediated by human ORC4, a protein component of the origin recognition complex. Biochemistry 2 18652488
2015 HsOrc4-Dependent Dna Remodeling of the ori-β Dhfr Replicator. Cellular & molecular biology letters 1 26124052

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