2026/01/27 by Chris Weekes, Lia Willerding, Sanjay Khadayate +9 · 1 voice
Biochemistry, Genetics and Molecular Biology · #DNA Repair Mechanisms #Microtubule and mitosis dynamics #Epigenetics and DNA Methylation
paper · pdf · doi:10.64898/2026.01.27.699880
SUMMARY During eukaryotic DNA replication initiation, inactive MCM2–7 double-hexamers assembled at replication origins must be converted into two active CMG helicases, yet how this transition is coupled to origin DNA unwinding in vivo remains unclear. Here, we identify a DNA-bound intermediate with an extended genomic footprint that forms during helicase activation. Genome-wide mapping of initial strand separation reveals that DNA unwinding initiates near the N-terminal interface of opposing MCM2–7 hexamers. At these sites, the origin DNA exhibits a conserved AT-rich/GC-rich/AT-rich sequence architecture on which the helicase complex is centred, consistent with a role in promoting DNA extrusion following double-hexamer separation. We further show that restricting hexamer rotation and splitting delays release of the Cdc45-loading factor Sld3, demonstrating that mechanical transitions during helicase activation are tightly coupled to complex disassembly. Finally, we provide in vivo evidence that single-stranded DNA is ejected through a specialised DNA exit gate at the Mcm2/5 interface during helicase activation, which is dispensable for ongoing DNA synthesis. Together, these findings establish a mechanistic framework for how replication origins are remodelled to initiate DNA replication and reveal key intermediates and DNA transactions during helicase activation.