The effects of enzymatic attack and of shear during the isolation and deproteinization of DNA have been investigated. Different methods of disaggregating DNA have been studied, and conditions under which reaggregation can occur are discussed. It was found that shaking with chloroform-octanol does not degrade DNA from the seven sources studied; that light scattering yields valid weight-average molecular weights for these samples; and that, when disaggregated, the molecular weights of these samples are in the range 1.2-2.4 million and the length-to-mass ratios are high.

Synchronized cells of a normal human lymphocytic cell line contain little swiven enzyme activity in G0 and G1 and high activity in Sphase. The level of activity in different growth phase appears to be related to the fraction of the population engaged in DNA replication. No endogenous inhibitor or activator of swiven activity could be demonstrated. The evidence implies that the enzyme may be present only during S phase; it is therefore a possible control factor for replication.

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