Recovery from Sublethal X-Ray Damage in Surviving Yeast Cells

Since the introduction of single-cell culture techniques (1), the nature of radiation-induced damage leading to cell death has been studied extensively. In general, the X-ray survival curves of mammalian cells cultured in vitro have two characteristics: an initial shoulder, followed by an exponential fall (2). Such kinetics suggest that the cells have been damaged to varying amounts (3) and that a definite amount of damage must accumulate before a cell is killed. Thus, on the first part of the curve many cells have received sublethal damage, but when the curve becomes exponential all the cells have received the maximum amount of sublethal damage and cannot survive any further damage. Elkind and Sutton (3) performed experiments on cells of the Chinese hamster cultured in vitro to determine whether the sublethal damage was transmitted by the surviving cells to their progeny, or whether this damage was repaired prior to cell division. Using fractionated X-ray doses, they found that the damage caused by the first fraction of the dose was rapidly repaired by the surviving cells, and if such cells were then subjected to a second fraction they behaved as normal cells that had never been irradiated.