Dark Recovery Phenomena in Yeast: I. Comparative Effects with Various Inactivating Agents

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Abstract
If X-irradiated diploid cells of Saccharomyces cerevisiae are stored for 3-5 days in the dark in distilled water or phosphate buffer at 30 [degree]C, their viability as determined by plating is much greater than if they are plated im -mediately after irradiation. A similar storage effect is observed after treatment with ultraviolet light or nitrogen mustard, but not after heat inactivation or acridine-sensitized photoinactivation. Control experiments demonstrate that the recovery does not arise from postirradiation cell multiplication in the storage medium. This process is characterized by a constant dose-modifying factor which varies for the different inactivating agents. Following exposure to UV, the dark recovery is partially additive to photoreactivation. Ploidies higher than diploid also exhibit recovery; on the other hand, haploid yeast does not recover from X-ray inactivation and displays only slight recovery from UV or HN2 inactivation.