The Deoxyribonucleases of Escherichia coli

There are a number of enzymes present in cell-free extracts of Escherichia coli which can degrade deoxyribonucleic acid (DNA) and smaller polynucleotides derived from it (l-3). One of these enzymes, although unable to hydrolyze high molecular-weight DNA at an appreciable rate, will rapidly hydrolyze DNA which has undergone some prior degradation; it is in this respect analogous to the classical phosphodiesterase of snake venom (4). The purpose of this report is to describe in detail the purification and properties of this enzyme which will be referred to as the Escherichia coli phosphodiesterase. This diesterase has been found to hydrolyze E. coli and calf thymus DNA’s to their constituent 5’-mononucleotides once these polymers have undergone some degradation as a result either of heating or limited treatment with pancreatic DNase. The E. coli phosphodiesterase is also capable of degrading appropriately pretreated bacteriophage DNA’s bearing glucosylated hydroxymethyl cytosine to their constituent mononucleotides. In this respect, it differs from the venom diesterase, which is unable to catalyze the cleavage of most of the linkages in which glucosylated hydroxymethyl cytosine is involved (5-7). In further contrast to the venom diesterase, the E. coli phosphodiesterase cannot hydrolyze either free dinucleotides or the 5’-terminal dinucleotide portion of a polydeoxynucleotide chain.