The Deoxyribonucleases of Escherichia coli

Abstract

Abstract 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.