The Deoxyribonuclease Induced after Infection of Escherichia coli by Bacteriophage T5

The major deoxyribonuclease induced by bacteriophage T5, as previously studied (Paul, A. V., and Lehman, I. R., J. Biol. Chem., 241, 3441 (1966)), has been purified 400-fold and has been shown to initiate hydrolysis specifically at the 5'-ends of either single or double stranded DNA. The products of hydrolysis are nucleoside 5'-monophosphates and acid-soluble 5'-phosphoryl-terminated oligonucleotides of varying lengths. The average length of the oligonucleotides is 3 residues. The purified exonuclease preparation is free from significant levels of endonuclease activity as measured on circular DNA substrates. The oligonucleotide products can therefore not be accounted for by endonucleolytic hydrolysis. The purified enzyme, in contrast to exonucleases like Escherichia coli exonuclease III, can degrade ultraviolet-irradiated DNA.