Measurement of local DNA reorganization on the picosecond and nanosecond time scales

Picosecond and nanosecond dynamics in the interior of DNA are observed for the first time as a dynamic Stokes shift in the fluorescence of a specially designed base-pair analogue. A recently synthesized coumarin C-riboside ha s been incorporated into an oligonucleotide in place of a normal purine pyr imidine base pair. The dynamic Stokes shift of this probe occurs with compo nents near 300 ps and 13 ns. These times are too long for solvent relaxatio n or simple vibrational motion of the DNA framework. They imply that the in terior of DNA is a unique dynamic environment unlike either a fluid or a mo lecular crystal.