Local de-condensation of double-stranded DNA in oppositely charged polyelectrolyte as induced by spermidine.

How polyamines such as spermidine cooperate with histone to condense and de-condense DNA during transcription has not been clarified. In this work, using the complex of DNA and poly(L-lysine) (PLL) at +/- ratio of 0.5 as a model of nucleosome, we monitored the de-condensation of DNA in the presence of spermidine. As revealed by the results from atomic force microscopy and time-resolved laser light scattering, spermidine was able to transform the spherical complex into a core-shelled structure, with the hard core being the DNA-PLL complex and the soft shell being DNA and spermidine. The soft shell evolved into a coiled DNA conformation with time. Such a local de-condensation process should be helpful in understanding the DNA transcription and cell division process in vivo.