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Updated: Mar 15, 2026
Author Spotlight: Investigating the Motion Dynamics of the Eukaryotic Replisome Components at the Single-Molecule Level
Published on: July 26, 2024
GINS complex protein Sld5 recruits SIK1 to activate MCM helicase during DNA replication
Kiranmai Joshi1, Varun Jayeshkumar Shah2, Subbareddy Maddika1
1Laboratory of Cell Death & Cell Survival, Centre for DNA Fingerprinting and Diagnostics (CDFD), Nampally, Hyderabad 500001, India.
Abstract:
In eukaryotes, proper loading and activation of MCM helicase at chromosomal origins plays a central role in DNA replication. Activation of MCM helicase requires its association with CDC45-GINS complex, but the mechanism of how this complex activates MCM helicase is poorly understood. Here we identified SIK1 (salt-inducible kinase 1), an AMPK related protein kinase, as a molecular link that connects GINS complex with MCM helicase activity. We demonstrated that Sld5 a component of GINS complex interacts with SIK1 and recruits it to the sites of DNA replication at the onset of S phase. Depletion of SIK1 leads to defective DNA replication. Further, we showed that SIK1 phosphorylates MCM2 at five conserved residues at its N-terminus, which is essential for the activation of MCM helicase. Collectively, our results suggest SIK1 as a novel integral component of CMG replicative helicase during eukaryotic DNA replication.
Insights
Salt-inducible kinase 1 (SIK1) links the GINS complex to MCM helicase, phosphorylating MCM2 to activate DNA replication. SIK1 is crucial for CMG helicase function in eukaryotes.
Area of Science:
- Molecular Biology
- Cell Biology
- Biochemistry
Background:
- DNA replication initiation requires MCM helicase loading and activation at origins.
- MCM helicase activation depends on the CDC45-GINS complex, but the mechanism remains unclear.
Purpose of the Study:
- To identify novel factors involved in MCM helicase activation.
- To elucidate the mechanism by which the CDC45-GINS complex activates MCM helicase.
Main Methods:
- Yeast two-hybrid screening to identify interacting proteins.
- Immunoprecipitation and Western blotting to confirm interactions.
- RNA interference (RNAi) to deplete SIK1.
- In vitro kinase assays and site-directed mutagenesis to study phosphorylation.
Main Results:
- SIK1 (salt-inducible kinase 1) was identified as a protein interacting with Sld5, a GINS complex component.
- SIK1 is recruited to replication sites at the start of S phase.
- SIK1 depletion causes defective DNA replication.
- SIK1 phosphorylates MCM2 at five N-terminal residues, which is essential for MCM helicase activation.
Conclusions:
- SIK1 acts as a molecular link between the GINS complex and MCM helicase.
- SIK1-mediated phosphorylation of MCM2 is critical for activating the MCM helicase.
- SIK1 is a novel, integral component of the CMG (CDC45-MCM-GINS) replicative helicase in eukaryotes.
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