Hfr-mediated conjugative transfer of pBR322 vector carrying the chromosomal DNA of Escherichia coli.

Hybrid plasmids consisting of a non-mobilized plasmid, pBR322, and a segment of chromosomal DNA of Escherichia coli could be transferred from an Hfr donor to recipient cells by a bacterial mating. When the chromosomal DNA in the plasmid corresponded to the early transfer region of the Hfr, the frequency of the transfer was high. The recA function of both donor and recipient cells was required in the transfer. The physical association of the hybrid plasmid with the transferring Hfr chromosome through the homologous sequences may mediate the transfer of the non-mobilized plasmid. This phenomenon is useful for the determination of the chromosomal location of an unidentified fragment cloned in a non-mobilized plasmid.