摘要：

The enzymatic degradation of DNA has been followed by a continuous titration method and simultaneously by light scattering or viscosity. The resulting data, which are in terms of the number of bonds broken per parent molecule and the molecular weight decay, are compared with the expected molecular weight decay, calculated on the basis of several simple models. The results indicate that the molecule is composed of two polynucleotide strands and that the enzyme cleaves phosphorusester linkages at random. The maximum number of contiguous hydrogen bonds which fail to keep two fragments united is estimated at 2 pairs at 25°. Non-coincident ester-bond breaks have little effect on the over-all molecular configuration. The intact double helix appears to be "free-draining" in character, as evidenced by the simple proportionality between intrinsic viscosity and molecular weight; this is in contrast to the impermeability of free polynucleotide chains. Finally, it appears that a double helix in which there are numerous interruptions in the polynucleotide chains is incompatible with the evidence.

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