[The possible role of rare tautomers of DNA bases in mutagenesis: study of the effect of hydration on tautomeric equilibrium by the Monte-Carlo method].

Monte Carlo simulation of hydration of keto and enol tautomers of 9-methylguanine (G) and 1-methyluracil (U) has been performed in relation to a possible role of tautomer transitions of DNA bases in mutagenesis. The comparison of the simulation results with published experimental data and results of quantum mechanical computations leads us to conclusion about difference in the origins of keto-form prevalence in water solutions of G and U. Such a reason for uracil (thymine) is a greater intrinsic stability of keto tautomer while the more preferable hydration of keto form of G is the reason of its predominance. As a consequence, during biosynthesis less hydrophylic environment (as compared to water solution) can be a reason for guanine transition into enol form and can result in mispair formation. Such a mutation mechanism is of a minor probability through thymine (uracil) tautomerization.