Replicative Form II DNA of ϕX174; Resistance to Exonucleolytic Cleavage by E. coli DNA Polymerase

The progeny replicative form II DNA isolated from E. coli cells infected with ϕX174 is resistant to the exonucleolytic activity associated with E. coli DNA polymerase. A limited endonucleolytic cleavage with micrococcal endonuclease renders the replicative form II molecule susceptible to the exonucleolytic activity associated with the E. coli DNA polymerase.