[Genetic control of F' factor production. III. Isolation of a mutant strain of Escherichia coli with reduced frequency and altered specificity of F' plasmid production].

Isolation and properties of the mutant of HfrH with altered frequency and specificity, of F'-plasmid formation are described. This mutant, designated fpf-5, showed significant reduction in the total yield of transconjugants selected for proximal markers in the cross with the F- recA- recipient. The crosses between the fpf-5 mutant donor and recA-nalA- recipient were sterile. The fpf-5 mutation resulted in the marked changes of the frequency of recombination exchanges involving definite chromosomal regions. The mutation reduced the frequency of the recA-independent recombination in the chromosomal fragment flanked by the leu and proA, sharply decreased the frequency of the recA-dependent and completely blocked recA-independent recombination in the chromosomal regions bordered by the genes proA and gal. Moreover the fpf-5 mutation affected the process of conjugative F'-plasmid formation suggesting effect of the mutation on recombinational exchange between the chromosome and integrated F-plasmid. The data obtained confirmed our earlier conclusion about fundamental role of the Hfr donor cell in the determination of the frequency and specificity of recombination leading to the F'-plasmid formation, and showed that the recombination events initiating F'-formation process occur in the Hfr donor cell.