[Interactions of derivatives of short oligonucleotides with nucleic acids. VII. Effect of conformation changes in the duplex structure on on the specificity and efficacy of modification of target DNA by alkylating oligonucleotide derivatives].

The modification of a target DNA by alkylating oligonucleotide derivatives possessing various capacities for complex formation was studied. The binding properties of oligonucleotides were changed either by increasing their length (tetra-, octa-, and dodecamers) or by introducing a point substitution and/or an N-(2-hydroxyethylphenazinium) residue. It was found that conformational changes occurring in the structure of the target.reagent complex upon elevating the reaction temperature affect the efficiency and site-specificity of the alkylation. In the case of complete saturation of the target with the reagent, an increase in the hybridization ability of the reagent reduced the efficiency of the target modification. It was found that the modification by the tetranucleotide reagent (in the presence of an effector adjacent to the 3' end) occurs exclusively at an intracomplex target base. In the case of the dodecamer, which forms a stable, highly cooperative complex with the target, several bases of the target undergo alkylation, and an increase in temperature changes the site-specificity of alkylation. In this process, the redistribution of the target modification sites toward stronger nucleophilic centers enhances alkylation at temperatures near the melting temperature of the target.dodecanucleotide complex despite a decrease in the extent of target association.