Isolation of High-Frequency Recombining Strains from Escherichia coli Containing the V Colicinogenic Factor

The isolation and characterization of high-frequency recombining strains from differentEscherichia 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. Fv + segregants of these were isolated, and the Fv 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.