The inhibition of precursor incorporation into DNA by ionizing radiations in HeLa S3 cells is a time-dependent phenomenon, maximum inhibition being achieved 1-3 hours after irradiation with doses of 400-2000 rads. The shape of the dose-response curve for incorporation of14 C-thymidine over a short interval of time is therefore strongly dependent on the time at which incorporation is measured. The phenomenon may be further influenced by medium replacement following irradiation, which dampens the inhibition. The kinetics of depression are identical for random and synchronous populations in the S phase at the time of exposure. Pool changes do not seem to play an important role in the fluctuations observed. HeLa cells irradiated in S do not show a compensatory acceleration of DNA synthesis following the inhibition induced by x-rays: rather, they continue to make DNA at a slower rate, but for an extended time. When replication ceases the incorporation is at least as great as in the controls; in a significant n...
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Barbara G. Weiss (1971) studied this question.