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. We comment on the biological implications to detect, by spectroscopic measurements, such an unusual structure involved in the stability, protection and replication maintenance along the human telomeric G-rich strand.