Detachment of segments from DNA double strands as detected by time resolved Rayleigh light scattering

Calf thymus DNA was irradiated oxygen saturated 0.01 N NaCl solution with 2 mus pulses of 15 MeV electrons. By monitoring the decrease of light scattering intensity after the pulse, two modes of decrease were detected: The fast decrease (tau 1/2 approximately 0.8 ms) is ascribed to the separation of DNA fragments produced by double strand breaks at positions directly opposite to each other. The slow decrease (tau 1/2 approximately 8 s) is attributed to the detachment of segments generated by single strand breaks at sites on the alternate strands being separated by about 10 nucleotide units.