Isolation and Characterization of Enzymes with Nicking Action from Phage T4-infected Escherichia coli

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Abstract
From phage T4-infected cells of Escherichia coli B, two enzymes, A and B, with nicking action were isolated. Both enzymes introduced single strand breaks (nicks) in native DNA of Bacillus subtilis, but yielded no significant amount of acid-soluble materials. The nicks were repaired by treatment with polynucleotide ligase isolated from the same organisms. The repair was demonstrated by the sedimentation analysis in the alkaline sucrose density gradient and the transformation technique. Enzyme A is most active at pH 6.0 and gives a limited number of nicks per DNA strand. The sites that enzyme A preferentially attacks seem to be determined by special base sequences extending over G. G and G. A bonds. Enzyme B is most active at pH 9.0. The question whether or not these enzymes deserve to be called nicking enzymes is discussed.

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