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Molecular basis of the essential s phase function of the rad53 checkpoint kinase

Nicolas C Hoch1, Eric S-W Chen, Robert Buckland

  • 1St. Vincent's Institute of Medical Research, Fitzroy, Victoria, Australia.

Molecular and Cellular Biology
|June 12, 2013
PubMed

Insights

The essential yeast kinase Rad53 regulates DNA replication by controlling deoxynucleoside triphosphate (dNTP) levels and activating the Dun1 kinase. Ultralow catalytic activity is sufficient for normal replication if Dun1 activation is maintained.

Area of Science:

  • Molecular Biology
  • Cell Cycle Regulation
  • DNA Replication and Repair

Background:

  • The roles of essential kinases like Mec1/ATR and Rad53/Chk1 in DNA damage response are well-established.
  • Their requirement for DNA replication in unperturbed cells is less understood.
  • Understanding these roles is crucial for comprehending genome stability.

Purpose of the Study:

  • To elucidate the essential S phase function of the yeast kinase Rad53.
  • To investigate the specific mechanisms by which Rad53 regulates DNA replication.
  • To determine the contribution of Rad53's phosphorylation sites and catalytic activity to its essential functions.

Main Methods:

  • Genetic analysis of yeast mutants, including phosphosite mutants (rad53-4AQ) and kinase-deficient mutants (rad53-K227A).
  • Synthetic lethality assays to identify essential gene interactions.
  • Analysis of deoxynucleoside triphosphate (dNTP) levels and replication fork stability.
  • Investigation of downstream kinase activation, specifically Dun1.

Main Results:

  • The rad53-4AQ mutant, lacking N-terminal Mec1 phosphorylation sites, is synthetically lethal with rad9 deletion due to impaired Dun1 activation.
  • This impairment leads to reduced dNTP levels, replication fork stalling, and constitutive S phase checkpoint activation.
  • Kinase-deficient rad53-K227A is viable but becomes inviable with mutations preventing Dun1 binding, indicating the importance of Rad53-Dun1 interaction.
  • Minimal Rad53 catalytic activity suffices for replication if Dun1 activation is preserved.

Conclusions:

  • Rad53's essential S phase function relies on both regulating basal dNTP levels and its kinase activity for compensatory responses.
  • Targeting Rad53 for Dun1 activation is critical for maintaining replication fidelity.
  • These findings highlight a dual role for Rad53 in ensuring genome stability during DNA replication.

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