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Visualizing and Quantifying Endonuclease-Based Site-Specific DNA Damage

Visualizing and Quantifying Endonuclease-Based Site-Specific DNA Damage

Published on: August 21, 2021

DNA mismatch repair-induced double-strand breaks.

Anetta Nowosielska¹, M G Marinus

¹Department of Biochemistry and Molecular Pharmacology, University of Massachusetts Medical School, 364 Plantation Street, Worcester, MA 01605, USA.

|September 11, 2007

Summary

This summary is machine-generated.

Escherichia coli dam mutants exhibit sensitivity to DNA damaging agents like cisplatin and MNNG. Mismatch repair (MMR) influences double-strand break formation, with replication-dependent and independent mechanisms contributing to cytotoxicity.

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Analysis of DNA Double-strand Break (DSB) Repair in Mammalian Cells

Analysis of DNA Double-strand Break (DSB) Repair in Mammalian Cells

Published on: September 8, 2010

Area of Science:

Molecular Biology
Genetics
DNA Repair

Background:

Escherichia coli dam mutants show increased sensitivity to cytotoxic agents such as cisplatin and N-methyl-N'-nitro-N-nitrosoguanidine (MNNG).
Mismatch repair (MMR) deficiency confers tolerance to these agents.
Previous studies indicated MMR-mediated double-strand breaks (DSBs) in dam recB(Ts) cells treated with cisplatin.

Purpose of the Study:

To investigate the mechanisms of double-strand break (DSB) formation in Escherichia coli dam mutants exposed to DNA damaging agents.
To elucidate the roles of DNA replication and mismatch repair (MMR) in DSB formation and cytotoxicity.

Main Methods:

Pulse field gel electrophoresis (PFGE) to detect double-strand breaks (DSBs).
Treatment of dam mutants (dam recB(Ts) and dam recB(Ts) ada ogt) with cisplatin and MNNG.
Analysis of DSB formation in relation to DNA replication and MMR status.

Main Results:

The majority of cisplatin-induced DSBs in dam recB(Ts) cells require DNA replication, suggesting replication fork collapse at MMR-processed nicks/gaps.
MNNG induced dose- and MMR-dependent DSBs in dam recB(Ts) ada ogt cells, independent of DNA replication.
Two distinct mechanisms for DSB formation were proposed: replication-independent (overlapping repair tracts) and replication-dependent (replication fork collapse at O(6)-methylguanine undergoing MMR futile cycling).
Fast-growing cells with more replication origins showed increased sensitivity to MNNG, supporting the role of replication-dependent DSBs in cytotoxicity.

Conclusions:

DNA damaging agents induce DSBs through distinct replication-dependent and replication-independent pathways in Escherichia coli.
Replication fork collapse at MMR-processed lesions contributes significantly to MNNG-induced cytotoxicity.
The interplay between DNA replication, MMR, and DNA damage dictates the cytotoxic outcome.