Sublethal damage, potentially lethal damage and lethal damage produced by ionizing radiations

It is thought that expression of sublethal damage (SLD) would never occur. SLD produced by the first exposure to ionizing radiations would be completely repaired 12 hr later, and there are no interactive abilities of SLDs that are produced by the first and second exposures. There is some evidence that SLD is a manifestation of lesions in DNA or DNA degradation and that the repair of SLD is the repair of DNA degradation. Potentially lethal damage (PLD) is recognized as cell damage that occurs depending on physical and chemical conditions after irradiation. Two types of PLD, slow-type PLD (s-PLD) and fast- type PLD (f-PLD), were seen when the cells were incubated in growth medium with phosphate-buffered saline after irradiation. Both types of PLD exhibited independent repair processes with individual genes involved in PLD repair. In addition, the repair processes of SLD and PLD have proved to be different. The previous observations have suggested that s-PLD is break at chromosome levels involved in double strand breaks of DNA; and that f-PLD is damage at the DNA-nucleoid matrix membrane. The more recently available data have supported the hypothesis that lethal damage is a manifestation of double strand breaks of DNA, indicating that different genetic mechanisms at G1 and S phases are responsible for the repair of double-strand breaks. (Namekawa, K.)