Abstract
We demonstrate that fluorescence correlation spectroscopy (FCS) can be employed to follow the conformational changes of DNA molecules induced by the addition of a cationic condensing compound (spermine). In our experiments the plasmid pHβAPr-1-neo (10 kbp; contour length 3.4 m) was labeled with propidium iodide (PrIo) and then titrated with spermine to induce its condensation. When spermine was applied at concentrations above 5 M (spermine/DNAphosphate =0.375), the diffusion time of the labeled plasmid dropped from 15 ms down to 3 ms (its diffusion coefficient, D, increased from 1.010 exp 12 square m/s to 6.010 exp 12 square m/s). The application of spermine was also accompanied by decreasing count rate and particle number, reflecting the dyes dissociation. The data presented show that FCS may become a valuable tool in studying supramolecular aggregate formation, especially when association is followed by a change in the hydrodynamic size of the resulting complex.
Copyright © 2002 by Walter de Gruyter GmbH & Co. KG
