Dynamics of superhelical DNA studied by photon correlation spectroscopy

摘要: Abstract We have conducted photon correlation spectroscopy (PCS) studies on the plasmid pUC8 (2717 bp) in order to elucidate internal dynamics of this superhelical DNA. confirm that first-order autocorrelation function scattered light from solutions can be separated into two distinct exponential decay components, as first shown by Lewis et al. (R. Lewis, J.H. Huang and P. Pecora, Macromolecules 18 (1985) 944). A thorough analysis dependence scattering vector K rates amplitudes components enables us assign slowly relaxing part center-of-mass diffusion DNA, while faster component corresponds rotational, bending twisting motions superhelix. For larger values formally expressed terms an ‘internal coefficient’ Di, whose value 2.0–2.5×10−11 m2 s−1 is approximately equal translational coefficient predicted for a stiff DNA piece persistence length, 65 nm. Comparison our measured Di those recent theory circular worm-like coils (K. Soda, 17 (1984) 2365) shows are than theoretical values. One reasons discrepancy could does not take account torsional motions, which contribute significantly (J.C. Thomas, S.A. Allison, C.J. Appelof J.M. Schurr, Biophys. Chem. 12 (1980) 177). At low values, fast relaxation rate no longer proportional K2, but reaches constant approaches zero. This behavior, seen linearized interpreted rotational flexible rod-like molecule (T. Maeda S. Fujime, 2381) supports interwound structure with average end-to-end distance 220