The action of colicin E2 on supercoiled lambda DNA.II. Experiments in vitro

An in vitro system has been developed to test whether colicin E2 possesses DNase activity. Purified colicin E2 preparations introduced one single-strand scission in supercoiled lambda phage DNA. Glycerol gradient fractionation of colicin E2 supports the association of in vitro action with in vivo cell-killing activity. Colicin E2 preparations also attacked superhelical SV40 DNA yielding open circles and fragments and single-stranded fd DNA molecules causing one or more endonucleolytic breaks. The possible role of contaminating nucleases in the activity of colicin E2 preparations is discussed.