DNA single-strand rejoining in two pairs of cell-lines showing the same and different sensitivities to X-rays

SummaryThe numbers of single-strand breaks and their rates of rejoining have been compared in two Yoshida cell-lines showing similar sensitivity to X-rays (D0 85 rads, n = 2·5) and two L5178Y cell-lines showing differential sensitivity; the sensitive cell-line having a D0 value of 55 rads, n = 2·5, and the resistant line a D0 value of 160 rads and n = 3·0. After doses of 5 or 10 krads, no differences in the numbers of single-strand breaks produced or in their rates of rejoining were observed when measured by the alkaline sucrose gradient technique. The findings confirm that single-strand breaks in themselves are not lethal events, since similar numbers are produced and virtually all are rejoined in the cell-lines studied. However, a deficiency in some of the processes involved in repair replication could be the cause of their differential sensitivity by allowing damage to be fixed.