A small DNA restriction fragment with an apparent permanent dipole moment

The electric birefringence of two DNA restriction fragments, each containing 147 base-pairs, has been investigated. The decay of the birefringence was the same for the two fragments, with a relaxation time corresponding to the reorientation of fully extended, rod-like molecules. However, the birefringence saturation behavior of the two fragments was markedly different: one fragment oriented by the expected induced-dipole mechanism, while orientation of the other fragment followed the theoretical curve for permanent dipole orientation. This difference in behavior must be due to differences in the base-pair sequences of the two fragments.