Repressor-minus and operator-constitutive de-repressed mutants of F-like R factors: their effect on chromosomal transfer by HfrC

Abstract

Certaindrdmutants offi⁺R factors, when carried by strain HfrC, allowed polarized transfer of the Hfr chromosome to occur at the normal rate. These mutants were independently shown to be repressor-sensitive and so owed their de-repression to failure to produce represser (i⁻). With otherdrdmutants, independently shown to be repressor-insensitive (0^c), the rate of polarized chromosome transfer was as low as with the wild type and only R pili were produced by the HfrC⁺bacteria. These R factors, therefore, continued to produce repressor and the donor behaviour of an Hfr strain depends on functioning of the integrated F.