SUB-CHROMOSOMAL DNA-SYNTHESIS IN X-IRRADIATED V-79 CELLS

The effect of X radiation on DNA replication in Chinese hamster V-79 cells has been investigated by DNA fiber autoradiography. The only effect observed at the replicon level is a reduction in the frequency of initiation events. The dose-response for this reduction is multiphasic indicating that some initiation events are much more radioresistant than others. When the data obtained from DNA fiber autoradiography are compared to kinetic data for thymidine incorporation, it is evident that at least for V-79 cells, the effects of X radiation on thymidine uptake into acid-precipitable material can be entirely accounted for by alterations in the frequency of initiation of replicon clusters.