[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; 8.4, 6.0, 4.5, 3.4 A. Low-angle reflections at 84 and 42 A are present also in X-ray patterns of compact particles, formed from DNA molecules with altered secondary structures. These two reflections are believed to be the results of an ordering of DNA molecules within the compact particles. The main features of this ordering appear in the first approximation to be independent on DNA secondary structure. The CD spectra of all types of compact particles, mentioned above, were also studied. It has been shown that the intense negative band (lambda approximately 270 nm) in a CD spectrum appeared only in the case of compact particles, formed from native DNA molecules. The nature of the revealed correlation between the 35 A reflection and the CD negative band is discussed. Data presented in the paper allow one to suppose that the 35 A reflection in X-ray patterns and the CD negative band result from specific interactions between double-stranded DNA fragments spatially brought together in compact particles. Such type of interaction is believed to be characteristic only of native DNA molecules.