Study of DNA-spermine interactions by use of small-angle and wide-angle X-ray scattering and circular dichroism

Abstract

Circular dichroism measurements with DNA-spermine complexes at 0.075 M NaCl and at 0.15 M NaCl reveal'+4' (type I) and -W (type II) CD spectra respectively. From small-angle X-ray scattering studles it could be shown that type I has a long-range order, short-range order supramolecular structure, while type II is of long-range disorder, short-range disorder structure. The secondary structure of the DNA in both types of condensates is B-like as concluded from wide-angle X-ray scattering diagrams of the condensates and from a comparison with the wide-angle X-ray curves of DNA and RNA in solution.

DNA mesophases induced by spermidine: structural properties and biological implications

“…Solutions of DNA and spermidine remain isotropic in the presence of a high concentration of monovalent salt. A dilution of the solution induces the aggregation of DNA by lowering the NaCl concentration, as reported previously (Damaschun et al, 1978;Becker et al, 1979). These data were used to follow under the microscope the formation of the birefringent aggregates, when drops of distilled water were added to a solution of DNA and spermidine.…”

“…In extremely dilute solution (less than 1 to about 10 Ag/ml), a monomolecular collapse (when only one molecule is involved) or the formation of microaggregates can occur, and polyamine-DNA complexes form either tores (Gosule and Schellman, 1976;Chattoraj et al, 1978;Baeza et al, 1987) or spheres (Chattoraj et al, 1978). In dilute solutions (about 1 mg/ml), the aggregates are large enough to sediment in a pellet (Damaschun et al, 1978).…”

Condensed states of nucleic acids. III. Ψ(+) and Ψ(−) Conformational transitions of DNA induced by ethanol and salt

“…The glucosylation of this DNA prevents it from adopting A-form ge0rnetry.~3,~~ Thus, as in the case of *(-) DNA,1° the compacted @(+) state appears to form directly from B-DNA helices A hich retain the major features of their secondary structure. 26 The contrasting x-ray-scattering result found for DNA precipitates formed at 80% (w/w) ethanol, namely the presence of predominantly A-form helices,53,54 does not conflict with the view that \k(+) condensation occurs without significant secondary structural changes in the DNA; it simply means that whatever the supramolecular arrangement of the \k( +) state, According to Lang, the maximally condensed state of ethanol-dehydrated DNA consists of third-order super coil^,^^,^^ whereas Eickbush and Moudrianaki@ assigned to it a folded-fiber conformation. We tend to favor the second model, since that fits better with the earlier interpretations of PEO-induced *( -) state, as well as with the work on DNA crystals grown from ethanolic s o l~t i o n .~~-~~ Lerman has shown by freeze-fracture etching these crystals that the helices are arranged parallel to each other, perpendicular to the broad surface of the ~r y s t a l .~~,~~ Thus, we conclude that the most compact aggregates observed in solution (or more properly, perhaps, suspension) contain locally parallel helical molecules which may fold back upon themselves at those surfaces which are perpendicular to the general direction of the helix axes.…”

Calculation of scattering curves for macromolecules in solution and comparison with results of methods using effective atomic scattering factors

“…The scattering curve of randomly oriented molecules in solution contains information on conformational parameters, e.g. on the rise per base pair, the turn angle between neighbouring base pairs, the distance r of the atoms from the helix axis and the number of coherent scattering base pairs as discussed for doublehelical nucleic acids by Langridge et al (1960), Bram & Beeman (1971), Bram (1971), Ninio, Luzzati & Yaniv (1972), Maniatis, Venable & Lerman (1974), Damaschun, Damaschun, Becker, Buder, Misselwitz & Zirwer (1978), Mfiller, Damaschun, Welfle & Bielka (1981), Becker, Misselwitz, Damaschun, Damaschun & Zirwer (1979). Whereas for a shape determination of the molecules from small-angle X-ray scattering the influence of the solvent need not be taken into account, the solvent, in general, changes the scattering curve of the molecule at larger angles.…”