Repair-induced Changes in Yeast Radiosensitivity

Potentially lethal X-ray or ultraviolet damage in the diploid yeast, Saccharomyces cerevisiae, can be reversed if the irradiated cells are incubated in distilled water or buffer for a number of hours prior to plating. This phenomenon is called liquid-holding recovery. We found that the liquid-holding procedure served not only to restore the viability of the irradiated cells, but also to alter their sensitivity to further doses of radiation. Specifically, the ultraviolet sensitivity of cells which had undergone liquid-holding recovery was markedly decreased, whereas their X-ray sensitivity appeared to be slightly increased. These sensitivity changes were qualitatively the same irrespective of whether the initial radiation exposure was to X rays or ultraviolet light. (In contrast, the radiation sensitivity of cells which had undergone maximal photoreactivation was essentially the same as that of untreated controls.) It is suggested that these changes in radiosensitivity are the result of structural alterations induced in the cell's deoxyribonucleic acid by the execution of at least the initial steps of a deoxyribonucleic acid repair process during the liquid-holding period.