Superhelical DNA studied by solution scattering and computer models.
We present here recent results on the structure of superhelical DNA and its changes with salt concentration between 0.01 and 1.5 M NaCl. Scattering curves of two different superhelical DNAs were determined by static light scattering. The measured radii of gyration do not change significantly with salt concentration. Small-angle neutron scattering, together with calculations from a Monte Carlo model, allows to determine the superhelix diameter. Measured and simulated scattering curves agreed almost quantitatively. Experimentally we find that the diameter decreases from 16.0 +/- 0.9 nm at 10 mM to 9.0 +/- 0.7 nm at 100 mM NaCl. The superhelix diameter from the simulated conformations decreased from 18.0 +/- 1.5 nm at 10 mM to 9.4 +/- 1.5 nm at 100 mM NaCl. At higher salt concentrations up to 1.5 M NaCl, the diameter stays constant at 9 nm.
Langowski
J
J
Deutsches Krebsforschungszentrum, Division Biophysics of Macromolecules (H0500), Heidelberg, Germany. joerg.langowski@dkfz-heidelberg.de
Hammermann
M
M
Klenin
K
K
May
R
R
Tóth
K
K
D003198:Computer Simulation; D004278:DNA, Superhelical / Q000737:chemistry*; D004926:Escherichia coli; D008027:Light; D009010:Monte Carlo Method; D009502:Neutrons; D010957:Plasmids; D012542:Scattering, Radiation; D012965:Sodium Chloride; D012996:Solutions
D004278:DNA, Superhelical; D012996:Solutions; D012965:Sodium Chloride