A method is described for the preparation of transforming DNA from 1 ml. samples of pneumococcal cultures of low density (e.g. about 10 bacteria). It seemed likely that the precipitation of very small amounts of transforming DNA from lysates of dilute pneumococcus cultures might result in loss of DNA unless a suitable co-precipitant was added. With high dilutions of transforming DNA, it was confirmed that such a loss was obtained. This loss was largely prevented by the addition of sodium hyaluronate in the presence of citrate. Dextran was not as efficient as hyaluronate as a co-precipitant.


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