Cell Cycle Checkpoint

droppedImageThe DNA damage checkpoint pathway enforces cell cycle arrest to allow timely repair in response to DNA damage and replication stress. We are studying which factors in the cell are responsible for recognizing damage in distinct stages of the cell cycle, and how they start the checkpoint pathway by activation of the kinase activity of Mec1/ATR, the initiating protein kinase in this signal transduction pathway. Remarkably, different activators of Mec1/ATR are utilized during different parts of the cell cycle, the checkpoint clamp 9-1-1 being most active during G1, whereas the complex of 9-1-1 with the replication initiation factor Dpb11/TopBP1 functions most efficiently during G2/M. Emerging data in our lab indicate that the replication checkpoint that functions in S phase in response to stalling of replication forks, involves activation of Mec1/ATR by components of lagging strand replication machinery. Our biochemical studies of Mec1/ATR activation are closely interconnected with complementary genetic analyses.