AI Insight
This study investigates how eukaryotic DNA replication is initiated by reconstituting the yeast pre-Initiation Complex from purified proteins and resolving its structure using cryo-electron microscopy. The results reveal how firing factors (Cdc45, GINS, and Pol epsilon) assemble stepwise onto a double hexamer of MCM ATPases to form two symmetric CMGE helicases, and how ATP drives ejection of firing factors and maturation of the complex. Additionally, the protein Sld2 is shown to play multiple roles beyond GINS recruitment, including facilitating CMGE dimer separation and enabling lagging strand ejection from MCM, with implications for its human ortholog RECQL4.
Why it matters
Understanding the molecular mechanism of replication initiation is fundamental to explaining how genome duplication errors arise, with direct relevance to diseases such as cancer where replication control is disrupted. The conservation of this mechanism across eukaryotes, suggested by the link to RECQL4, may inform research into replication-associated genetic disorders in humans.
⚠️ Preprint – Noch nicht peer-reviewed
Dieser Artikel wurde noch nicht von unabhängigen Experten begutachtet. Die Ergebnisse sind vorläufig und sollten mit Vorsicht interpretiert werden.
When cells enter S phase, bidirectional DNA replication is initiated through the kinase-regulated recruitment of three activators (Cdc45, GINS and Pol epsilon) to a duplex DNA-loaded double hexamer of MCM ATPases. Together these proteins form two CMGE helicases that establish divergent replication forks as they become separated. To understand CMGE biogenesis, we reconstituted the pre-Initiation Complex with purified yeast proteins. The cryo-EM structure shows a set of firing factors caught in the act of assembling two symmetric CMGEs. We show how stepwise complex formation reshapes MCM in preparation for DNA opening and we explain how ATP promotes firing-factor ejection and CMGE maturation. While we find that Sld2 promotes GINS recruitment to MCM as expected, it also aids efficient separation of the CMGE dimer, and it is essential for lagging strand ejection from MCM. These findings have direct implications for our understanding of the metazoan Sld2 ortholog, RECQL4, pointing to a replication-fork establishment mechanism conserved across eukaryotes.
Source: Structure of the Pre-Initiation Complex Explains CMGE Biogenesis