Bacteriophage T5-induced endonucleases that introduce site-specific single-chain interruptions in duplex DNA

Four site-specific endodeoxyribonucleases have been partially purified from extracts of bacteriophage T5-infected Escherichia coli by gel filtration and affinity chromatography on single- and double-stranded DNA. The enzymes were detected and characterized by agarose gel electrophoresis of alkali-denatured digestion products. None of the four is found in uninfected cells. In the presence of a divalent cation, all four endonucleases make ligase-repairable, single-chain interruptions at specific sites in the duplex DNA of several bacteriophages (lambda, T7, and T5) and a mammalian virus (adenovirus 2). These activities are not stimulated by ATP. None of the four is active on single-stranded DNA. The fragments produced by each enzyme from ligase-repaired T5 DNA do not correspond to those derived from mature T5 DNA. Each of the enzymes is able to cleave the intact strand of T5 DNA.