[Ultrasonic cleavage of DNA in complexes with Ag(I), Cu(II), Hg(II)].

We investigated a phenomenon of ultrasonic cleavage of DNA complexed with transition metal cations Ag(I), Cu(II) and Hg(II). We found the statistically significant dependence of relative intensity of cleavage on cation type and concentration. Each cation may cause two different types of distortion in the DNA double-helix depending on whether it binds to major or minor DNA groove. The intensity of ultrasonic cleavage decreases if cation binds to the major DNA groove; the intensity of cleavage increases if cation binds to the minor DNA groove and disturbs the hydrogen bonds of complementary base pairs or it intercalates between bases. Both types of DNA distortion can affect the intensity of N-S interconversion of deoxyribose.

[Cleavage of DNA fragments induced by UV nanosecond laser excitation at 193 nm].

The cleavage of dsDNA fragments in aqueous solution after irradiation with UV laser pulses at 193 nm has been studied. Samples were investigated using polyacrylamide gel electrophoresis. The intensity of damage of particular phosphodiester bond after hot alkali treatment was shown to depend on the base pair sequence. It was established that the probability of cleavage is twice higher for sites of DNA containing two or more successively running guanine residues. A possible mechanism of damage to the DNA molecule connected with the migration of holes along the helix is discussed.

[Heterogeneity of double-stranded DNA local structure and dynamics: ultrasound studies].

A method for studying the local inhomogeneities of DNA and its dynamics is proposed. The method is based on the combination of two procedures, splitting the DNA molecules by ultrasound and analysis of DNA fragments obtained by gel electrophoresis. The frequency of cleavage of internucleotide bonds was found to depend on the type of nucleotides forming the bond and on their nearest neighbors. Estimates of cleavage frequencies in each of 16 dinucleotides showed that, in the 5'-d(CpG)-3', 5'-d(CpA)-3', and 5'-d(CpT)-3' dimers, the cleavage occurs considerably more frequently than in the rest, and the frequency of cleavage depends on the nearest neighbors. It was shown that the double-helix cleavage can occur with shifts by several nucleotides. Physical prerequisites were considered that can lead to this pattern of sequence - specific cleavage.