An Exonuclease Induced by Bacteriophage λ

λ exonuclease exhibits a much greater rate of attack on native deoxyribonucleic acid than on denatured DNA, the difference in rate being 350-fold for T7 phage DNA. The attack is exclusively exonucleolytic, and the only acid-soluble products are deoxyribonucleoside 5‘-monophosphates. In contrast to the known Escherichia coli exonucleases, its initial site of attack is at the 5‘ termini of a DNA molecule, with a strong preference for termini bearing a phosphoryl residue as compared with those bearing a free hydroxyl group.