Abstract
We are irradiated with cosmic rays at about 280 uSv a year as natural background on the earth. It has been calculated on trial that the irradiation dose by cosmic rays presumably increase to be about 40 mSv when we stay in space station for 6 months, which is higher than 50 mSv a year, the dose limit for radiation workers. Radiation produces a wide range of different types of damages of DNA and induces mutation. Mutation is the result of error in the process of repair and replication of DNA. Mechanism of mutation induction has been studied in detail in Escherichia coli. Genes such as uvrA, B and C, and umuC/D express in the cells inducing SOS response, resulting in enhancement of repair capacity and of mutagenesis. Although enhancement of the capacity of DNA repair is observed in UV- or radiation-irradiated mammalian cells, it dose not presumably associate enhancement of mutagenesis. Mechanism of mutation induction in mammalian cells may be different from that in bacterial cells. Base substitution mutations are predominantly detected in plasmid or phage DNA replcating in E. coli. GC to AT transition is most frequent base substitution. Large deletion of DNA fragment in addition to base substitution and frameshift are observed in irradiated mammalian cell. Further studies should be performed on radiation-induced mutagenesis at molecular level.
