DNA Damages Caused by Irradiation of Near-ultraviolet Light and Their Repair

Abstract

Most of the investigations of ultraviolet(UV)-radiation effects on organisms have been made with 254nm from a germicidal lamp. The specific DNA lesion, pyrimidine dimers, caused by UV irradiation have been shown to be toxic, mutagenic and carcinogenic. In contrast, knowledge of the biological effects of far UV(UV-C) radiation may not be relevant to the carcinogenic, mutagenic and lethal effects of UV in sunlight. Recently, since it has been indicated that the DNA lesions caused by mid-UV(280-320nm, UV-B) and nearUV(320-400nm, UV-A) is harmful to a wide variety of organisms, the studies of mid-UV and near-UV effects are considered to be important. The possible DNA damages caused by mid-UV and near-UV are summarized in the present review. In mid-UV range, both the pyrimidine dimers and other photoproducts such as 5-hydroxy-methyl cytosine may be responsible for the observed biological effects and they are repairable by excision repair systems or T4 endonuclease. Several DNA damages of near-UV are indicated to be DNA strand breaks dependent on pol⁺ and nur⁺ repair systems, DNA-protein cross-links and a small amount of pyrimidine dimers which are responsible to repair deficint mutants including human patients. In addition, other kinds of photodamages in tRNA carrying cytidine 13 and thiouridine 8 link than DNA damage are indicated to also interact to repair processes.