The rotational dynamics of short DNA fragments with or without intrinsic cu
rvature were studied using time-resolved phase fluorimetry of intercalated
ethidium with detection of the anisotropy. Parameters determined were the s
pinning diffusion coefficient of the DNA fragments about the long axis and
the zero-time ethidium fluorescence anisotropy. We find a significant decre
ase in the spinning diffusion coefficient for all curved fragments compared
to the straight controls. This decrease is likewise evident in rotational
diffusion coefficients computed from DNA structures obtained by a curvature
prediction program for these sequences. Using: a hinged-cylinder model, we
can identify the change in rotational diffusion coefficient with a permane
nt bend of 13-16 degrees per helix turn for the sequences studied. Moreover
, for some of the curved fragments an increased flexibility has to be assum
ed in addition to the permanent bend in order to explain the data.