We are interested in origin firing through S phase. We showed that this is controlled by gradients of kinase activities. Basal ATR and CHK1 kinase activities inhibit origin firing
in undamaged cells
and this limits origin firing and DNA replication to accommodate rate-limiting concentrations of dNTPs and key replication proteins. The cyclin-dependent kinase CDK1 induces origin firing through S phase and then when it’s activity spikes the onset of mitosis. ATR and CHK1 kinase activities increase in cells treated with agents that damage replication forks and this arrests origin firing and DNA replication - the S phase cell cycle checkpoint.
We are interested in mechanisms that coordinate DNA replication and transcription in T regulatory and CD8+ T cells cultured ex vivo. Naive mice contain about 200 CD8+ T cells for a given p:MHC I complex. These 200 cells expand 500,000-fold in a few days to generate 10^7 cells at the peak of the primary response. CD8+ T cells have evolved with unique mechanisms that facilitate rapid DNA replication and cell division.
We are interested in mechanisms that distinguish the DNA damage responses associated with normal DNA metabolism that remain localized at a
DNA double-strand break or damaged replication fork, and the cellular DNA damage response above some threshold of lesions that induces cell cycle checkpoints. ATM kinase activity is increased within seconds of exposure to 0.05 Gy ionizing radiation or following the induction of just two DNA double-strand breaks and this activity orchestrates DNA repair. More than 50% of ATM molecules are activated following exposure to 0.5 Gy ionizing radiation and this activity induces the G1 cell cycle checkpoint as well as DNA repair. Understanding the
mechanisms that distinguish
these DNA damage responses is important as the sequence of treatment with a DNA damaging chemotherapy and DNA damage response inhibitor will determine the damage induced by the combination.