DNA-strand scission and loss of viability after x irradiation of normal and sensitized bacterial cells.

Abstract

Irradiation of Escherichia coli induced a decrease in sedimentation rate of alkali-denatured and native DNA, attributable to single- and double-strand scission, respectively. Singlestrand scissions were repaired during reincubation of the irradiated cells, whereas double-strand scissions were not. BUdR increased the yield of double-strand scissions to the same extent (threefold) as it increased radiation lethality. It is concluded that double-strand scissions in DNA are the radiochemical lesions principally responsible for the lethal effect of ionizing radiation in E. coli. However, single-strand scissions are probably important in radiosensitive mutants lacking the repair system, and perhaps also in ceUs grown under conditions in which repair is inhibited.