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Title | A dual role for the chromatin reader ORCA/LRWD1 in targeting the origin recognition complex to chromatin. |
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Journal, issue, pages | EMBO J, Vol. 42, Issue 18, Page e114654, Year 2023 |
Publish date | Sep 18, 2023 |
Authors | Sumon Sahu / Babatunde E Ekundayo / Ashish Kumar / Franziska Bleichert / |
PubMed Abstract | Eukaryotic cells use chromatin marks to regulate the initiation of DNA replication. The origin recognition complex (ORC)-associated protein ORCA plays a critical role in heterochromatin replication ...Eukaryotic cells use chromatin marks to regulate the initiation of DNA replication. The origin recognition complex (ORC)-associated protein ORCA plays a critical role in heterochromatin replication in mammalian cells by recruiting the initiator ORC, but the underlying mechanisms remain unclear. Here, we report crystal and cryo-electron microscopy structures of ORCA in complex with ORC's Orc2 subunit and nucleosomes, establishing that ORCA orchestrates ternary complex assembly by simultaneously recognizing a highly conserved peptide sequence in Orc2, nucleosomal DNA, and repressive histone trimethylation marks through an aromatic cage. Unexpectedly, binding of ORCA to nucleosomes prevents chromatin array compaction in a manner that relies on H4K20 trimethylation, a histone modification critical for heterochromatin replication. We further show that ORCA is necessary and sufficient to specifically recruit ORC into chromatin condensates marked by H4K20 trimethylation, providing a paradigm for studying replication initiation in specific chromatin contexts. Collectively, our findings support a model in which ORCA not only serves as a platform for ORC recruitment to nucleosomes bearing specific histone marks but also helps establish a local chromatin environment conducive to subsequent MCM2-7 loading. |
External links | EMBO J / PubMed:37551430 / PubMed Central |
Methods | EM (single particle) / X-ray diffraction |
Resolution | 1.8 - 2.9 Å |
Structure data | EMDB-40522, PDB-8siy: PDB-8siu: |
Chemicals | ChemComp-SO4: ChemComp-HOH: |
Source |
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Keywords | PROTEIN BINDING / chromatin binding / ORC binding / REPLICATION / nucleosome |