We are interested in how
eukaryotic cells sense and respond to stress in the form of damage to
their genetic material. When cells incur DNA damage or under go DNA replication
interference, they arrest the cell cycle via cell cycle checkpoint pathways
and induce the transcription of genes involved in repair of the damage.
Failure to do this can result in genomic instability and cancer in humans.
To investigate how eukaryotic cells accomplish this task, we have isolated
mutations in genes that block the ability of yeast cells to sense DNA
damage and established a genetic pathway. We have found that sensors of
DNA damage and replication blocks activate a kinase cascade involving
the Mec1, Rad53, Dun1 and Chk1 protein kinases in yeast. Mec1 controls
the activation of Rad53, which controls activation of Dun1, and activation
of Chk1 which controls phosphorylation of the anaphase inhibitory protein
Pds1. Dun1 controls the phosphorylation and inhibition of a transcriptional
repressor, Crt1, that binds at multiple sites to the promoters of damage-inducible
genes. Phosphorylated Crt1 no longer binds to promoter DNA, allowing the
activation of the target genes. Crt1 also binds to its own promoter and
is induced in response to DNA damage, thereby participating in an auto-inhibitory
feedback loop that facilitates return to the repressed state.
|
