Protection of foreign DNA against host-controlled restriction in bacterial cells. I. protection of F' plasmid DNA by preinfection with bacteriophages T3 or T7.

Foreign F'lac plasmid DNA which is introduced into potentially restricting E. coli recipient cells can be protected from restriction by preinfecting the recipient cells with UV-inactivated T3 or T7 bacteriophages which express the ocr gene function. The recipient cells survive and are able to replicate themselves as well as the newly acquired plasmid.