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Regulation of DNA replication fork progression through damaged DNA by the Mec1/Rad53 checkpoint

J A Tercero1, J F Diffley

  • 1Imperial Cancer Research Fund, Clare Hall Laboratories, South Mimms EN6 3LD, UK.

Nature
|August 3, 2001
PubMed

Insights

Checkpoint kinases Mec1 and Rad53 protect Saccharomyces cerevisiae from DNA damage. Preventing replication fork collapse is key to cell viability during DNA alkylation.

Area of Science:

  • Molecular Biology
  • Cell Biology
  • Genetics

Background:

  • Checkpoint kinases Mec1 and Rad53 are crucial for maintaining cell viability in Saccharomyces cerevisiae when facing DNA damage or replication stress.
  • These proteins are believed to function by halting cell cycle progression, thereby allowing time for DNA repair.
  • Mec1 and Rad53 also slow S phase progression in response to DNA alkylation, but the precise mechanism and its significance remain unclear.

Purpose of the Study:

  • To investigate the role of Mec1 and Rad53 in regulating DNA replication fork progression during exposure to the DNA-alkylating agent methyl methanesulphonate (MMS).
  • To elucidate the mechanism by which Mec1 and Rad53 protect cells from DNA alkylation-induced cytotoxicity.

Main Methods:

  • Utilized Saccharomyces cerevisiae as a model organism.
  • Applied methyl methanesulphonate (MMS) to induce DNA damage and replication stress.
  • Compared DNA replication fork progression and cell viability in wild-type and checkpoint-deficient (mec1, rad53) yeast strains.

Main Results:

  • MMS significantly reduced DNA replication fork progression, but this effect did not require Mec1 or Rad53.
  • Checkpoint mutants exhibited accelerated S phase due to aberrant initiation events.
  • Replication forks in checkpoint mutants collapsed irreversibly at high rates in the presence of MMS.
  • Cytotoxicity of MMS in checkpoint mutants was observed specifically when cells entered S phase with DNA damage.

Conclusions:

  • The primary role of Mec1 and Rad53 in response to DNA alkylation is not to slow replication forks but to prevent inappropriate initiation events.
  • Preventing damage-induced DNA replication fork catastrophe is a critical mechanism by which these checkpoints maintain cell viability.
  • Checkpoint integrity is essential for preventing irreversible replication fork collapse and subsequent cell death when cells encounter DNA damage during S phase.

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