Physical properties of endonuclease S1 digestion products of DNA renaturation intermediates

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Abstract
The growth of the weight‐average double‐strand length of renaturing sonicated DNA was investigated as a function of the degree of renaturation. Endonuclease S1 was used to digest single‐strand ends and gaps. The ratio of the average renatured length to the initial length was found to be 0.6 ± 0.1 early in the reaction and to approach 1.0 at infinite time, while the ratio of the average single‐strand length of native regions increased from 0.6 ± 0.1 to 0.8 ± 0.1 at infinite time. The ratio increases are nonlinear, with the greatest growth occuring around 50% renaturation. Relaxation times of double‐strand DNA were measured in low salt using alternating field electric birefringence and were found to increase to only 70% of the relaxation time of the initial DNA at infinite time. In the molecular‐weight range examined (150–320,000 daltons), relaxation times vary with the 2.3 ± 0.3 power of molecular weight.