M. Hammermann et al., SALT EFFECTS ON THE STRUCTURE AND INTERNAL DYNAMICS OF SUPERHELICAL DNAS STUDIED BY LIGHT-SCATTERING AND BROWNIAN DYNAMICS, Biophysical journal, 73(5), 1997, pp. 2674-2687
Using laser light scattering, we have measured the static and dynamic
structure factor of two different superhelical DNAs, p1868 (1868 bp) a
nd simian virus 40 (SV40) (5243 bp), in dilute aqueous solution at sal
t concentrations between 1 mM and 3 M NaCl. For both DNA molecules, Br
ownian dynamics (ED) simulations were also performed, using a previous
ly described model. A Fourier mode decomposition procedure was used to
compute theoretical light scattering autocorrelation functions (ACFs)
from the ED trajectories. Both measured and computed autocorrelation
functions were then subjected to the same multiexponential decompositi
on procedure, Simulated and measured relaxation times as a function of
scattering angle were in very good agreement. Similarly, computed and
measured static structure factors and radii of gyration agreed within
experimental error. One main result of this study is that the amplitu
des of the fast-relaxing component in the ACF show a peak at 1 M salt
concentration. This nonmonotonic behavior might be caused by an initia
l increase in the amplitudes of internal motions due to diminishing lo
ng-range electrostatic repulsions, followed by a decrease at higher sa
lt concentration due to a compaction of the structure.