DNA fusion product of phage P2 with plasmid pBR322: a new phasmid.

The chromosome of the temperate bacteriophage P2 and that of the plasmid pBR322 have been joined in vitro after treatment with restriction endonuclease EcoRI. The fusion product - a phasmid - can behave as a plasmid, as a phage and as a prophage. It can replicate its DNA under the control of either the specific replication mechanism of the parent phage in a polA mutant or that of the parent plasmid in a rep mutant. Several interesting interactions between the two replication modes are indicated. In particular, phage particles may be produced even when the phage mode of DNA replication is blocked, and this throws new light on the involvement of the early gene A in the regulation of late gene expression in phage P2.