An Endonuclease Induced after Infection of Escherichia coli with Bacteriophage T7

The deoxyribonuclease purified from Escherichia coli infected with bacteriophage T7 catalyzes an endonucleolytic cleavage of both single- and double-stranded DNA. During the hydrolysis of duplex DNA single-strand breaks are introduced. These interruptions can be repaired by incubation in the polynucleotide ligase reaction. Prolonged incubation of native DNA with the enzyme leads to fragmentation of the DNA, as measured by sedimentation analysis in neutral sucrose gradients. Hydrolysis of native DNA yields polynucleotides bearing 5'-phosphory1 and 3'-hydroxyl termini; the 5'-end groups are predominantly pyrimidine residues. Extensive hydrolysis of denatured T7, native T7, and native E. coli DNA yields products having average molecular weights of 6 x 103, 1 x 105, and 6 x 103, respectively.