Metabolic Repair of Premutational Damage in Paramecium

The problems of experimental analysis of the post-irradiation processes leading to mutation are considered in some detail. In particular, methods for separating the effects of various modifiers on the rate of these processes from the effects on the time available for them to occur are discussed. Data are presented for recessive lethal mutations in Paramecium to show that all metabolic inhibitors tried (caffeine, iodoacetate, chloramphenicol and streptomycin) decrease the rate of loss of premutational damage and decrease mutation only because they increase the time available for loss. The results are shown to fit the hypothesis of metabolic repair of radiation-induced lesions of the chromosomes.