DNA polymerase α and β activities during the cell cycle and their role in heat radiosensitization in Chinese hamster ovary cells

The levels of DNA polymerase α and β activities were measured during the cell cycle using a total cell homogenate technique. The results indicate a decrease in the levels of both enzyme activities during the G1 phase and a gradual increase as cells enter the S phase. The recovery of DNA polymerase activities was measured after heating for 10 min at 45.5°C during the G1 phase (1.5 hr after mitotic release) or S phase (8-9 hr after mitotic release). This treatment reduced the levels of DNA polymerase β activity to 20-30% and DNA polymerase α activity to 40-50% of their control activity for both G1 and S phase. The activity of DNA polymerase β recovered fully during 20-25 hr after heating for both G1 phase or S phase cells. There was no recovery of the activity of DNA polymerase α during this time. Survival was measured when cells were irradiated (4 Gy) at various times after hyperthermia (10 min at 45.5°C), and for both G1 and S phase the interaction between heat and X rays disappeared by 20-25 hr after heating and the same increase was observed for the recovery of DNA polymerase β activity. Furthermore, treatment with cycloheximide inhibited protein synthesis and prevented recovery from heat damage assayed in terms of both cell survival and β polymerase activity. These results, in addition to experiments with heat protection by glycerol or thermotolerance induced with sodium arsenite or fractionated heat doses, suggest that β polymerase may be an important enzyme involved in repairing X-ray-induced damage that can result in cell lethality.