[The action of hyperthermia on DNA repair (author's transl)]

The time-course of DNA repair after gamma irradiation was measured in HeLa cells at various temperatures. Unscheduled DNA synthesis was estimated by incorporation of 3H-thymidine in presence of hydroxyurea. To detect the ligase reaction, the number of single strand breaks (SSB) was determined by centrifugation in alcaline sucrose as well as by hydroxylapatite chromatography after partial denaturation. In addition, the temperature dependence of DNA polymerase and DNase reaction in cell-free systems were measured. These data were compared with the reduction of colony-forming ability of the cells caused by gamma irradiation and following repair at various temperatures. All steps of repair proceed faster at 41--43 degrees than at 37 degrees but cells are most resistant to gamma irradiation at 37 degrees. We therefore assume that the DNA repair process at 42 degrees is faster but more error prone than at 37 degrees.