- EMDB-19186: Cryo-EM structure of the MCM double hexamer loaded onto dsDNA. -
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Basic information
Entry
Database: EMDB / ID: EMD-19186
Title
Cryo-EM structure of the MCM double hexamer loaded onto dsDNA.
Map data
Relion Refine3D map
Sample
Complex: MCM-double hexamer loaded onto double-stranded DNA
Protein or peptide: x 6 types
DNA: x 2 types
Ligand: x 4 types
Keywords
MCM helicase / DNA replication / REPLICATION
Function / homology
Function and homology information
MCM core complex / Assembly of the pre-replicative complex / Switching of origins to a post-replicative state / MCM complex binding / nuclear DNA replication / premeiotic DNA replication / replication fork protection complex / pre-replicative complex assembly involved in nuclear cell cycle DNA replication / mitotic DNA replication / Activation of the pre-replicative complex ...MCM core complex / Assembly of the pre-replicative complex / Switching of origins to a post-replicative state / MCM complex binding / nuclear DNA replication / premeiotic DNA replication / replication fork protection complex / pre-replicative complex assembly involved in nuclear cell cycle DNA replication / mitotic DNA replication / Activation of the pre-replicative complex / CMG complex / nuclear pre-replicative complex / Activation of ATR in response to replication stress / DNA replication preinitiation complex / MCM complex / double-strand break repair via break-induced replication / mitotic DNA replication initiation / single-stranded DNA helicase activity / regulation of DNA-templated DNA replication initiation / silent mating-type cassette heterochromatin formation / DNA strand elongation involved in DNA replication / nuclear replication fork / DNA replication origin binding / DNA replication initiation / subtelomeric heterochromatin formation / DNA helicase activity / transcription elongation by RNA polymerase II / helicase activity / heterochromatin formation / single-stranded DNA binding / DNA helicase / chromosome, telomeric region / DNA replication / DNA damage response / chromatin binding / ATP hydrolysis activity / zinc ion binding / nucleoplasm / ATP binding / nucleus / cytoplasm Similarity search - Function
Journal: Nat Struct Mol Biol / Year: 2025 Title: Cell cycle regulation has shaped replication origins in budding yeast. Authors: Chew Theng Lim / Thomas C R Miller / Kang Wei Tan / Saurabh Talele / Anne Early / Philip East / Humberto Sánchez / Nynke H Dekker / Alessandro Costa / John F X Diffley / Abstract: Eukaryotic DNA replication initiates from genomic loci known as origins. At budding yeast origins like ARS1, a double hexamer (DH) of the MCM replicative helicase is assembled by origin recognition ...Eukaryotic DNA replication initiates from genomic loci known as origins. At budding yeast origins like ARS1, a double hexamer (DH) of the MCM replicative helicase is assembled by origin recognition complex (ORC), Cdc6 and Cdt1 by sequential hexamer loading from two opposed ORC binding sites. Cyclin-dependent kinase (CDK) inhibits DH assembly, which prevents re-replication by restricting helicase loading to the G1 phase. Here, we show that an intrinsically disordered region (IDR) in the Orc2 subunit promotes interaction between ORC and the first loaded, closed-ring MCM hexamer (the MCM-ORC (MO) intermediate). CDK-dependent phosphorylation of this IDR blocks MO formation and DH assembly. We show that MO stabilizes ORC at lower-affinity binding sites required for second hexamer loading. Origins comprising two high-affinity ORC sites can assemble DH efficiently without MO by independently loading single hexamers. Strikingly, these origins escape CDK inhibition in vitro and in vivo. Our work reveals mechanistic plasticity in MCM loading with implications for understanding how CDK regulation has shaped yeast origin evolution and how natural, strong origins might escape cell cycle regulation. We also identify key steps common to loading pathways, with implications for understanding how MCM is loaded in other eukaryotes.
Cryogen name: ETHANE / Chamber humidity: 100 % / Chamber temperature: 283 K / Instrument: FEI VITROBOT MARK IV
Details
Complete biochemical reaction containing the MCM helicase in complex with Cdt1, the helicase loader (the origin recognition complex), the co-factor Cdc6, an origin or replication (DNA) flanked by nucleosomes, the regulatory kinase CDK and an inhibitor of CDK (Sic1). The sample was incubated with ATP yielding a range of structural intermediates in the MCM loading pathway.
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Electron microscopy
Microscope
FEI TITAN KRIOS
Specialist optics
Energy filter - Slit width: 20 eV
Image recording
Film or detector model: GATAN K2 SUMMIT (4k x 4k) / Detector mode: COUNTING / Digitization - Frames/image: 1-40 / Number real images: 24506 / Average electron dose: 51.2 e/Å2
Electron beam
Acceleration voltage: 300 kV / Electron source: FIELD EMISSION GUN
Number selected: 178188 Details: MCM-DH particles after first 2D classification from a dataset containing multiple molecular species (e.g. ORC, MCM-SH, MCM-DH)
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