Mitotic CDK Promotes Replisome Disassembly, Fork Breakage, and Complex DNA Rearrangements

Area of Science:

• Molecular Biology
• Genetics
• Cell Biology

Background:

• DNA replication errors contribute to human diseases like cancer.
• Entering mitosis before DNA replication completion is a known trigger for these errors.

Purpose of the Study:

• To investigate the molecular mechanisms by which mitosis affects DNA replication.
• To identify how unreplicated DNA is handled during mitotic entry.

Main Methods:

• Utilized Xenopus egg extracts to model early cell division.
• Employed biochemical assays to track protein modifications and interactions.
• Observed cellular events in C. elegans early embryos.

Main Results:

• Mitotic CDK (Cyclin B1-CDK1) induces ubiquitylation of the CMG (CDC45/MCM2-7/GINS) helicase on its MCM7 subunit.
• TRAIP, an E3 ubiquitin ligase, mediates CMG ubiquitylation.
• The CDC48/p97 ATPase extracts ubiquitylated CMG from chromatin.
• CMG removal at stalled forks leads to breakage and DNA rearrangements, including deletions and insertions.

Conclusions:

• Identified a novel mitotic pathway for replisome disassembly.
• Demonstrated that CMG unloading during mitosis can cause replication fork collapse.
• This process contributes to chromosomal instability and tumorigenesis.