Bleomycin-treated DNA is specifically cleaved only by endonuclease IV in E. coli

We have isolated an endonuclease from E. coli active on bleomycin-treated DNA. Purification on DEAE-cellulose separated this activity in strains lacking endonuclease I, endonuclease III or exonuclease III. After DEAE chromatography, the enzyme was active in the absence of divalent cations and was not inhibited by tRNA or harmane. In addition, this enzyme was stable at 45 degrees C for 20 min. These properties are consistent with this activity being endonuclease IV. This was supported by our finding no activity in a strain lacking endonuclease IV.