A role for the spindle assembly checkpoint in the DNA damage response.

Spontaneous DNA damage poses a continuous threat to genomic integrity. If unchecked, genotoxic insults result in genomic instability, a hallmark of cancer cells. In eukaryotic cells a DNA Damage Response (DDR) detects and responds to genotoxic stress, acting as an anti-cancer barrier in humans.

Three Different Pathways Prevent Chromosome Segregation in the Presence of DNA Damage or Replication Stress in Budding Yeast.

A surveillance mechanism, the S phase checkpoint, blocks progression into mitosis in response to DNA damage and replication stress. Segregation of damaged or incompletely replicated chromosomes results in genomic instability. In humans, the S phase checkpoint has been shown to constitute an anti-cancer barrier.

G1 cyclin driven DNA replication.

The mitotic cell cycle is driven by Cyclin-Dependent Kinases (CDK). CDK activation requires the binding of activatory subunits termed cyclins. Different waves of cyclins are expressed during the cell cycle, enabling CDKs to trigger phase specific events.

A Dbf4 mutant contributes to bypassing the Rad53-mediated block of origins of replication in response to genotoxic stress.

An intra-S phase checkpoint slows the rate of DNA replication in response to DNA damage and replication fork blocks in eukaryotic cells. In the budding yeast Saccharomyces cerevisiae, such down-regulation is achieved through the Rad53 kinase-dependent block of origins of replication. We have identified the Rad53 phosphorylation sites on Dbf4, the activator subunit of the essential S phase Dbf4-dependent kinase, and generated a non-phosphorylatable Dbf4 mutant (dbf4(7A)).

Cyclin regulation by the s phase checkpoint.

In eukaryotic cells a surveillance mechanism, the S phase checkpoint, detects and responds to DNA damage and replication stress, protecting DNA replication and arresting cell cycle progression. We show here that the S phase cyclins Clb5 and Clb6 are regulated in response to genotoxic stress in the budding yeast Saccharomyces cerevisiae. Clb5 and Clb6 are responsible for the activation of the specific Cdc28 cyclin-dependent kinase activity that drives the onset and progression of the S phase.