Radiation sensitivities are not related to the sizes of DNA supercoiled domains in L5178Y-R and L5178Y-S cells

Survival of murine lymphoblasts L5178Y-R and L5178Y-S irradiated with 60Co gamma radiation was determined. The parameters of the survival curves were D0 = 1.18 Gy, n 1.56 and D0 = 0.55 Gy, n = 1.00 for L5178Y-R and L5178Y-S cells respectively. The sizes of DNA supercoiled domains were estimated using sedimentation of nucleoids from cells irradiated with doses from 1 to 7 Gy. These sizes were 2.44 x 109 and 5.13 x 108 Da for L5178Y-R cells and 1.30 x 109 and 4.07 x 108 Da for L5178Y-S cells. Hence, higher radiosensitivity of L5178Y-S cells was not compatible with the larger size of the DNA supercoiled domains, as suggested by Filippovich et al. (1982). The authors did not find any simple relation between sizes of DNA supercoiled domains and the susceptibility of L5178Y sublines to ionizing radiation. (author)