[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. The temperature, at which this "melting" takes place (taum) increases with the rise of PEG concentration, but always remains below the melting temperature of the DNA secondary structure. The thermodynamic parameters, deltaH and deltaS, which characterize the "melting" of the microcrystalline regions in DNA compact particles, were calculated for each CD "melting" curve and were shown in increase, similarly to taum, with the rise of PEG concentration. These data indicate that the regularity of the internal structure of DNA compact particles depends not only on the structural characteristics of the initial DNA, but also on the solvent properties, in particular, on the PEG concentration.