Tautomeric Transitions in DNA

We study the tautomeric transitions in base pairs of DNA considering elastic properties of DNA as classical and tunneling of protons as quantum, and show that the dynamics of the transitions admits of soliton like solutions whose shape and size strongly depend on the structure of the double helix. In particular, we have found that the set of discrete breathers can be drastically modified by the interplay of the torsional and elastic constants. Our results may have a bearing upon substitution mutagenesis within the framework of Watson-Crick's approach, and in this respect the breather soliton could describe conformations corresponding to point mutations. The numerical simulation of soliton dynamics suggests that an initial distribution of base pairs with low probability of mutation per pair but of a sufficiently large number of base pairs involved, could move and gather around a site so as to form a set of base pairs with high probability of mutation, for a period of time approximately 1 µsec. We suggest that the irradiation of DNA at frequencies of the proton tunneling, that is in infra-red region, could cause mutations.