The role of structural water in the formation of nucleotide mispairs.

The results of NMR investigation of the double-helical nucleic acid fragments containing A.C, C.U, m6G.U and m6G.G mispairs can be explained on the assumption that the bases in such pairs being in usual tautomeric forms are linked via water bridges. A computer analysis of intermolecular interactions in the systems containing two bases and one or two water molecules shows that these pairs correspond to the energy minima. The formation of pairs with water bridges can be considered an intermediate step in mutagenesis caused by some spontaneous errors arising during nucleic acid biosynthesis as well in mutagenesis induced by alkylating agents.