DNA packaging in water solutions induced by polylysine and spermidine

The conformation properties of the DNA molecule complexed with polylysine (PLL) and spermidine (Spd) were studied by circular dichroism (CD), ultraviolet spectrophotometry, dynamic light scattering (DLS), viscosimetry, and dynamic birefringence. Experimental data suggest that when the concentration ratio of the monomer residues of polylysine and DNA (N/P) in moles is smaller than unity, the viscosity changes but slightly, whereas when N/P > 1, it abruptly drops to solvent viscosity. This is accompanied by changes in optical anisotropy and in the circular dichroism spectra of DNA. DLS data indicate that for N/P > 1, compact discrete particles are formed.