Abstract
(1) The work done by the research unit (representative: S. Matsumura, National Institute of Genetics, Misima, Japan) on mutagenic studies with higher and lower organisms is summarized.(2) RBE for mutations is discussed and compared with RBE for somatic damages. It is pointed out that the apparent RBE for mutagenicity reflects not only the efficiency of premutation induction, but also that of the depression of repair mechanisms.(3) Combining the above mentioned considerations with the results of other authors, it is concluded that there are mutagenic factors differing with genome complexity in addition to those common to all living things.(4) The increase in resistance to radiation-induced DNA damages with genome complexity is more remarkable for UV than for 32P or X-rays.(5) Models based on the evolutionary standpoints are proposed for the origin of the UV resistance.(6) Based on the evolutionary viewpoints, a repair-tolerance model is proposed for mutagenesis to account for the differential factors in mutagenesis mentioned; the differential factors are the reflection of the difference in the mechanisms of repairing and tolerating premutational DNA damages among different organisms.
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