Isolation of high-frequency recombining strains from Escherichia coli containing the V colicinogenic factor.

The isolation and characterization of high-frequency recombining strains from different Escherichia coli host cells containing either the F factor or the Col V factor are described. The strains (with one exception) formed from three of the V(+) parents showed the same origin and polarity of transfer (xyl-arg-pro-trp-his-mal). The Hfr strains formed from the one remaining V(+) and the F(+) host cells showed a greater variety in their points of origin. In addition, several Hfr strains isolated from V(+) parents lost the ability to produce colicin V. F(v) (+) segregants of these were isolated, and the F(v) factors appeared to retain their preferential site for Hfr formation, but they lacked other propertes controlled by the Col V factor. Chromosomal integration of episomes and its relation to the fertility of F(+) and V(+) strains are discussed. Production of colicin V appeared to be uninfluenced by the state of the Col V factor within the cell.