EFFECT OF MILLIMETER RANGE ELECTROMAGNETIC WAVES ON COMPLEX-FORMATION OF ETHIDIUM BROMIDE AND HOECHST 33258 WITH DNA

In this work, the effect of millimeter range electromagnetic waves on the melting parameters of DNA complexes with ethidium bromide (EtBr) and Hoechst 33258 (H33258) has been studied. It has been shown that the millimeter wave irradiation of water-saline solutions of DNA complexes with ligands leads to significant changes in the water structure, which in turn results in relevant alteration of the thermodynamic characteristics of DNA–ligand complexes. It has also been shown that the irradiation of the water-saline solutions of DNA–H33258 complexes with millimeter waves of 64.5 GHz frequency results in the manifestation of the ligand specific interaction at the high ionic strengths, which is not observed in the absence of irradiation. With the millimeter wave irradiation, as a consequence of increasing of the degree of DNA hydration, the interaction mode of EtBr with DNA is non-specific to sequences, but the intercalation mode does not change.

ИЗУЧЕНИЕ СТРУКТУРЫ ДНК В ПЛЕНКАХ МЕТОДОМ ИК-ФУРЬЕ-СПЕКТРОСКОПИИ

The aqueous environment and ionic surrounding are the most important factors determining the conformation of DNA and its functioning in the cell. The specificity of the interaction between DNA and cations is especially pronounced with a decrease in water activity. In this work, we studied the B-A transition in high molecular weight DNA with a decrease of humidity in the film with different contents of Na+ ions using FTIR spectroscopy. The IR spectrum of DNA is not only very sensitive to the state of its secondary structure, but also allows us to estimate the amount of water bound to DNA. Upon dehydration of the DNA film, changes characteristic of the B-A transition were observed in the IR absorption spectrum. Using thermogravimetric analysis, it was shown that the degree of DNA hydration reaches the saturation level at a relative humidity of 60% and decreases slightly upon further drying. It has been established that with increasing Na+ concentration, the amount of water strongly bound to DNA decreases. Along with it, sodium ions destroy the hydration shell of DNA and are able to interact directly with phosphate groups.

Ultrahigh-resolution centrosymmetric crystal structure of Z-DNA reveals the massive presence of alternate conformations

The self-complementary d(CGCGCG) hexanucleotide was synthesized with both D-2′-deoxyribose (the natural enantiomer) and L-2′-deoxyribose, and the two enantiomers were mixed in racemic (1:1) proportions and crystallized, producing a new crystal form withC2/csymmetry that diffracted X-rays to 0.78 Å resolution. The structure was solved by direct, dual-space and molecular-replacement methods and was refined to anRfactor of 13.86%. The asymmetric unit of the crystal contains one Z-DNA duplex and three Mg2+sites. The crystal structure is comprised of both left-handed (D-form) and right-handed (L-form) Z-DNA duplexes and shows an unexpectedly high degree of structural disorder, which is manifested by the presence of alternate conformations along the DNA backbone chains as well as at four nucleobases (including one base pair) modelled in double conformations. The crystal packing of the presented D/L-DNA–Mg2+structure exhibits novel DNA hydration patterns and an unusual arrangement of the DNA helices in the unit cell. The paper describes the structure in detail, concentrating on the mode of disorder, and compares the crystal packing of the racemic d(CGCGCG)2duplex with those of other homochiral and heterochiral Z-DNA structures.