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Single-strand DNA breaks cause replisome disassembly
Kyle B Vrtis1, James M Dewar1, Gheorghe Chistol1
1Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Blavatnik Institute, Boston, MA 02115, USA.
Molecular Cell
|January 23, 2021
Summary
DNA nicks, abundant in cells, unexpectedly cause replication fork collapse by creating double-strand breaks. The CMG helicase (CDC45-MCM2-7-GINS) disassembles upon encountering these breaks, highlighting nicks as uniquely dangerous DNA lesions.
Area of Science:
- Molecular Biology
- Genetics
- Cell Biology
Background:
- DNA damage impedes replication and threatens genome stability.
- The CMG helicase (CDC45-MCM2-7-GINS) stalls at DNA adducts but usually resumes replication.
- The impact of single-strand breaks (nicks) on replication is poorly understood.
Purpose of the Study:
- To investigate how the CMG helicase responds to DNA nicks during replication.
- To determine the consequences of CMG encountering nicks on leading and lagging strands.
Main Methods:
- Utilized Xenopus egg extracts for in vitro replication studies.
- Examined CMG helicase behavior upon encountering DNA nicks.
Main Results:
- CMG collision with a leading strand nick creates a double-strand break (DSB), causing CMG to run off the break.
- CMG encountering a lagging strand nick leads to translocation beyond the break, ubiquitylation, and removal from chromatin.
- Nicks invariably cause replisome disassembly, unlike other DNA adducts.
Conclusions:
- DNA nicks are uniquely dangerous lesions that lead to replication fork collapse.
- The CMG helicase is removed from chromatin upon encountering nicks, preventing its storage on double-stranded DNA during replication stress resolution.
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