Stability of nucleic acid under the effect of UV radiation.

Nucleic acids (combined with protein molecules) are essential constituents of the living systems playing an important role in the early evolution of life as well. A specific feature of these molecules has been found and directly confirmed recently: under the influence of short-wavelength UV radiation bipyrimidine photoproducts (cyclobutane dimers and 6-4 bipyrimidines) are induced and the reversion of them can be provoked by the same photons. However, reversion is preferred by the shorter wavelengths. With increasing ratio of the longer wavelength components of the radiation (using artificial UV sources and solar light on the Earth's surface) the impact of the reversible photoproducts in the harmful biological effect decreases and other photoproducts are dominant. Assuming the photoinduced reactions (dimerisation and reversion) are statistical events, during the irradiation the chance for a number of nucleoprotein molecules to survive the radiation damage can be reality. The theoretical and experimental basis of these assumptions will be discussed in the case of bacteriophage T7 nucleoprotein.