Figure 2.

Biphasic Dose Response to DNA Damage. In response to DNA damage, cells reduce replication in a biphasic manner. In wild-type controls, initial reduction in DNA synthesis in response to low doses of ionizing radiation (IR) is steep (solid line) whereas declines in response to higher doses of IR is more shallow (dashed line). ATM checkpoint-kinase deficient cells do not display the initial steep reduction in synthesis in response to low doses of IR but do display similar response to wild-type controls at higher doses. Comparison between ATM and wild-type controls suggests that the shallow portion of the does-response curve may be checkpoint independent in nature. Figure adapted from [27].