Survival of major DNA damage such as the long segments of single-stranded DNA resulting from collapse of a replication fork, requires the assembly of a multiprotein complex that recognizes the damaged DNA and signals to the cell cycle machinery to halt cell division until the damage has been repaired. Failure in this response can result in aneuploid cell division and the genomic instability that is a common feature of cancer.

This DNA Damage Checkpoint apparatus involves recognition of the dsDNA-ssDNA transition by the 9-1-1 complex, coating of ssDNA with Replication Protein A, and coupling of these via the BRCT-domain scaffold protein TopBP1/Rad4. Together with a connection to modified chromatin via the damage mediator 53BP1/Crb2, this results in activation of the PI3-kinase-like kinase ATR, which in turn activates the effector kinase CHK1, arresting the cell cycle. We are working to understand the structural basis for the assembly of the DNA Damage Checkpoint apparatus, which is regulated by multiple post-translational modifications.