Kinetics of renaturation of denatured DNA. II. Products of the reaction

The structure of renatured T4 DNA has been studied by CsCl density-gradient centrifugation. It has been found that the products of the reaction differ, depending on the method used for denaturation of the DNA. If denaturation is carried out without taking precautions to prevent chain degradation, for example, by heat, the DNA formed by renaturation shows approximately 70% recovery of the native structure as judged by its density. With long times of annealing, the DNA can recover the native density. This behavior is also observed with bacterial DNA samples. On the other hand, if precautions arc taken to prevent chain degradation during denaturation, two products appear as a result of renaturation. One of them is undistinguishable from native T4 DNA, whereas the second one consists of highly aggregated DNA which shows only a partial recovery of the native structure. With long times of annealing, this second species recovers the native density but retains its highly aggregated nature. At higher ionic-strengths, renaturation follows a different pattern and a single product is formed. The relevance of all these observations to the kinetic anomalies reported in the previous communication is discussed.