[Inactivating and mutagenic effects of long-wave UV-light in bacteria with various mechanism of repair].

UV-radiation of 254 nm wavelength produces in the genetic material (desoxyribonucleic acid, (DNA) of bacteria photochemical alterations (lesions) which can lead to cellular death or mutation induction. The biologically most important class of these lesions is the one of the pyrimidine dimers. Bacteria possess three groups of enzymatic mechanisms which can eliminate such lesions under certain circumstances: elimination in situ; removal from the nucleotide chain (prereplication repair); ignoring the lesion (postreplication repair). The biological effect and the importance of these so-called repair mechanisms is reviewed and the occurrence in other organisms is briefly discussed. On the one hand, organisms are exposed to UV-radiation of 254 nm wavelength only under artificial conditions; on the other hand, long-wave solar UV-radiation (between approximately 300 nm and visible light) which amounts to about three per cent of the total energy output, represents the most powerful radiation to which organisms can be exposed under natural conditions to any larger extent. As outlined in the second part of this review, this radiation also induces lesions which may act as substrate for the above mentioned repair mechanisms. With increasing wavelength, lesions may also occur in cellular components other than DNA. The complexity of biological responses arising thereby is discussed.