Construction in vitro of “Phage-plasmid” chimerae: a new tool to analyse the mechanism of plasmid maintenance

In this paper, we report the construction in vitro of chimerae between lambdoid replacement vectors (Murray et al., 1977) and the miniF Apr plasmid: pSC138 (Timmis et al., 1975). λF recombinants were shown to be chimerae between the λ and the F replicons. By genetical tests, we have demonstrated that both λ and F replication mechanisms are functional: the λF recombinant behaves as a non defective plaque forming phage on λ sensitive bacteria and establishes itself as a stable plasmid on recA F- homoimmune bacteria. In the extra-chromosomal state, the λF recombinant apparently retains the controlled autonomous replication and the FI incompatibility characteristics of the F plasmid. The potential experimental uses of these phages are discussed.