Unusual salt-induced behaviour of guanine-rich natural DNA evidenced by dynamic light scattering.

The appearance of the slow mode, revealed by dynamic light scattering (DLS) measurements in Micrococcus luteus DNA with high GC content, and the effect of guanine sequences on changes of DNA physical state and conformational transitions were investigated. We used two different spectroscopic approaches: DLS, to evidence the relatively slowly diffusing particles arising at high salt concentration, ascribable to the formation of large unspecific molecular aggregates, and circular dichroism spectroscopy, to identify these entities. Our results bring us to conclude that a peculiar, unconventional, structural transition, due to the presence of long guanine stretches, in a well-defined experimental condition, can occur.

Light scattering study of natural DNAs over a wide range of molecular weights: Evidence for compaction of the large molecules.

This work reports light scattering measurements on DNA in aqueous solutions (100mM NaCl, 1mM EDTA and 10mM Tris-HCl buffer, pH 7.8) over a wide range of molecular weights (10(2)-10(5) base pairs) and shows that, in the above standard solvent, shorter chains (<10(4) base pairs) behave as a "wormlike chain" and their diffusion coefficients as obtained by dynamic light scattering measurements, confirm the prediction of standard wormlike model, whilst longer chains (>10(4) base pairs) behave in a different manner. Dynamic and static light scattering and SEM analysis indicate that DNA molecules 10(5) base pairs long, condense into compact structures in our solvent conditions.