Mathematical modelling of pirimidine photodimerization in polynucleotides

Three models of the interaction of UV radiation with one-chain pirimidine polynucleotide with a consideration of two possible types of contacts between closest bases (two types of initial dimers) and phenomenon of the excitation energy delocalization with/without the inclusion of the photodimers into the delocalization area are presented. The consideration of the two types of contacts and the inclusion of the photodimers into the delocalization area are made for the first time. In the frame of the models, which differ by the character of the excitation energy transfer to the photodimer, the dynamics of the photodimer accumulation in the polynucleotide under radiation and the dependence of the stationary concentration of the photodimers on the length of the delocalization were investigated for different types of the initial dimers without the heat equilibrium between initial dimers. It is shown that the inclusion of the photodimers into the delocalization area results in significant decrease of the equilibrium concentration of the photodimers. The consideration of the heat equilibrium between initial dimers does not break the effect. The proposed models with the energy transfer to the photodimer may describe the photoprocesses in the DNA of spores and some bacterium, which are highly resistant to the UV radiation.