The three-dimensional structure of supercoiled deoxyribonucleic acid in solution. Evidence obtained from the angular...

1. The size and shape of superhelical double-stranded circular DNA from bacteriophage ØX174 were investigated by light-scattering. The molecular weight of the DNA is 3.17x10(6) and the root-mean-square radius is 103.5nm. 2. The light-scattering envelopes of various theoretical three-dimensional models for such DNA molecules were calculated by repetitive computational techniques, and the results were compared with the experimental findings. 3. It is concluded that the structure of supercoiled DNA containing -12 superhelical turns in buffer of I0.2 corresponds best to one of the more compact models for superhelix structure such as the branched model, and the commonly employed straight interwound superhelix model is incompatible with the experimental results, at the superhelix density found.