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The Deoxyribonucleases of Escherichia coli

VII. A DEOXYRIBONUCLEASE INDUCED BY INFECTION WITH PHAGE T5

From the ¹ From the Department of Biochemistry, Stanford University School of Medicine, Palo Alto, California 94304

The increase in deoxyribonuclease activity after infection of Escherichia coli with bacteriophage T5 has been shown to be due to the synthesis of a DNase different from those known to be present in the host cell. During the course of T5 infection the enzyme appears at about the same time as the phage-induced deoxycytidylate kinase and DNA polymerase and only after most of the cellular DNA has been rendered acid-soluble.

Purification of the T5-induced DNase resulted in a preparation that is at least 80% pure, as judged by gel electrophoresis. The following properties of the purified enzyme have been established.

1. It has a pH optimum of 9.3 and requires Mg⁺⁺ or Mn⁺⁺ for maximal activity.

2. It can degrade either native or heat-denatured DNA.

3. Its mode of attack appears to be both endonucleolytic and exonucleolytic, yielding a mixture of small oligonucleotides with an average chain length of 4 to 5 and mono-nucleotides terminated with a 5'-phosphoryl group.

4. The proportion of mononucleotides produced from native E. coli DNA is about 4 times greater than that produced from heat-denatured DNA.

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