Properties of the clot assay, an easy quantitative assay of DNA endonucleases

A systematic examination of the properties of the clot assay, a highly sensitive and simple method to detect DNase activities, is presented. It is shown that it is both quantitative and specific for monitoring the double-strand cleavage of DNA produced by specific and nonspecific endonucleases. Its simplicity and ease of quantification, which exceeds that of other methods of similar sensitivity, indicates that the clot assay can be advantageous in monitoring the activity of both types of endonucleases, especially if carried out in parallel with other more informative assays on the mechanism of action of the enzymes. As an example of its use, it is shown that pancreatic DNase I is capable, in the absence of external metal addition, of a limited attack on DNA containing bound divalent cations.