Effect of netropsin on plasmid DNA cleavage by BAL 31 nuclease

BAL 31 nuclease is known to possess two sorts of catalytic activities: one is a single‐strand‐specific endonuclease activity that converts negatively supercoiled UNA to the unit‐length linear form, the other being a quasi‐processive exonuclease activity that simultaneously degrades both 3'‐ and 5'‐termini of linear dúplex DNA. Netropsin, a bactericidal and antiviral compound, was found to enhance the former activity but inhibit the latter. Netropsin‐bound supercoiled plasmid DNA had a tendency to be fragmented by BAL 31 into several species of linear DNAs smaller than full‐length size. Size reduction of linear plasmid DNA by BAL 31 was significantly inhibited by netropsin binding.