X-ray sensitivity and DNA synthesis in synchronous populations of HeLa cells.

Inhibition with either 5-fluorodeoxyuridine or deoxyadenosine for specified periods during the division cycle of the HeLa S3 cell shows that the mid-interphase peak in sensitivity occurs just before DNA replication begins. Sensitivity subsequently decreases only after synthesis of DNA is resumed. One interpretation of the relation between fluctuations in sensitivity and in DNA synthesis is that the lethal radiation damage to these cells occurs in DNA.