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Updated: Apr 26, 2026
Author Spotlight: Investigating the Motion Dynamics of the Eukaryotic Replisome Components at the Single-Molecule Level
Published on: July 26, 2024
Multiple functions for Mcm2-7 ATPase motifs during replication initiation
Sukhyun Kang1, Megan D Warner1, Stephen P Bell1
1Howard Hughes Medical Institute, Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
Abstract:
The Mcm2-7 replicative helicase is central to all steps of eukaryotic DNA replication. The hexameric ring of Mcm subunits forms six essential ATPases whose contributions to replication initiation remain unclear. Mcm2-7 complexes containing ATPase-motif mutations showed Mcm2-7 ATP binding and hydrolysis are required for helicase loading. Loading-defective Mcm2-7 mutant complexes were defective in initial Mcm2-7 recruitment or Cdt1 release. Comparison with Cdc6 ATPase mutants showed that Cdc6 ATP hydrolysis is not required for helicase loading but instead drives removal of Mcm2-7 complexes that cannot complete loading. A subset of Mcm2-7 ATPase-site mutants completed helicase loading but could not initiate replication. Individual mutants were defective in distinct events during helicase activation, including maintenance of DNA association, recruitment of the GINS helicase activator, and DNA unwinding. Consistent with its heterohexameric structure, our findings show that the six Mcm2-7 ATPase active sites are specialized for different functions during helicase loading and activation.
Insights
The Mcm2-7 helicase
Area of Science:
- Molecular Biology
- Cell Biology
- Biochemistry
Background:
- The Mcm2-7 complex is a crucial replicative helicase in eukaryotes.
- Its six ATPase sites' roles in DNA replication initiation are not fully understood.
Purpose of the Study:
- To investigate the specific functions of the Mcm2-7 ATPase active sites during DNA replication.
- To elucidate the roles of Mcm2-7 and Cdc6 ATPases in helicase loading and activation.
Main Methods:
- Utilized ATPase-motif mutations in Mcm2-7 complexes.
- Compared Mcm2-7 mutants with Cdc6 ATPase mutants.
- Assessed helicase loading, recruitment, Cdt1 release, and activation events.
Main Results:
- Mcm2-7 ATP binding and hydrolysis are essential for helicase loading.
- Cdc6 ATP hydrolysis is not required for loading but removes incompletely loaded complexes.
- Mcm2-7 mutants showed defects in replication initiation, DNA association, GINS recruitment, and unwinding.
Conclusions:
- The six Mcm2-7 ATPase active sites are specialized for distinct functions in helicase loading and activation.
- This specialization is consistent with the heterohexameric structure of the Mcm2-7 complex.
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