[Thermodynamic and spectral study of DNA-prospidin complex].

By the methods of heat denaturation and luminescence the interaction between an antitumor drug prospidine and DNA in aqueous solutions at two ionic strengths (0.1 and 0.001 M NaCl) and at various prospidine concentrations was studied.

[Use of the method of fast atom bombardment mass spectrometry for identification of products of the interaction of thiophosphamide with DNA].

Products of interaction between DNA and an antitumour drug N, N', N''-triethylenethiophosphoramide (thiotepa) have been observed for the first time by the fast atom bombardment mass spectrometry. The sites of alkylation are detected as N7 (Gua) and N3 (Ade), and yields of the products are evaluated.

[Compact form of synthetic polynucleotides. Relationship between secondary structure and circular dichroism spectra].

The formation of compact particles from synthetic double- and triplestranded polynucleotides in water-salt solutions, containing poly(ethylene glycol) (PEG) has been investigated. CD spectra of compact particles are characterized by intense bands (positive or negative) in the region of 270 nm, compact particles being divided into two families--psi- and psi+--according to the CD band sign. The amplitude of the CD band at 270 nm increases with the increase of CPEG.

[Compact form of DNA in solution. XII. Double-stranded polyribonucleotide compacting in the presence of polyethylene glycol].

Double-stranded polyribonucleotides (a replicative form of phage f2 RNA--dsRNA and poly(A) poly(U), can adopt a compact from in solutions, containing NaCl and poly(ethylene glycol) (PEG). According to electron-microscopic observations dsRNA compact particles have the form of disks or doughnuts 200--400 A in diameter. X-ray diffraction patterns from dense slurries of dsRNA compact particles show a reflection at a spacing of 35 A, which is indicative of the existance of ordered regions in compact particles.

[DNA compact form in solution. XI. Melting of the DNA compact state, formed in water-salt solutions, containing poly(ethylene glycol)].

Temperature dependences of absorption and CD spectra of DNA compact particles, formed in water-salt solutions in the presence of poly(ethylene glycol) (PEG), have been compared. It has been shown that the disappearance of a specific negative CD band, characteristic of the DNA compact form, occures prior to the destruction of the DNA secondary structure and is not connected with changes of the number or the size of compact particles. The disappearance of this band is believed to reflect the destruction of ordered structure of microcrystalline regions in DNA compact particles.

[DNA compact form. 8. X-ray diffraction study of DNA compact particles, formed in solutions containing polyethylene glycol].

A comparative X-ray study of DNA compact particles, formed in PEG-containing solution from native DNA and from DNA molecules with altered secondary structure was carried out. Low-angle reflections, present in X-ray patterns of compact particles (in powder form) from native DNA, correspond to spacings of 84, 42 and 35 A, while wide-angle reflections correspond to spacings of 12.8; 8.

[DNA compact form. VI. Changes of DNA secondary structure under conditions preceding its compaction in a solution].

Optical and thermochemical properties of E. coli DNA molecules are compared in solutions containing poly(ethyleneglycol) (PEG) in concentrations at which compactization is not yet observed. It is shown that under conditions preceding DNA compactization (CPEG less than 60 mg/ml) changes in CD spectra occur which suggest that the secondary structure of some DNA fragments is altered.

[The compact form of DNA in solution. IV. The effect of secondary structure defectiveness on the arrangement of double-chained DNA molecules into compact particles].

Influence of pH on absorbance and CD-spectra of DNA in PEG-containing water-salt solutions has been studied. The changes in the spectra appeared due to disturbance of the DNA secondary structure upon acidification of the medium proir to or after DNA compactization. If acidification preceeds DNA compactization an intense negative band in the CD spectrum inherent to the compact particles is observed at pH values 7-4.