Interactions between de-repressed F-like R factors and wild type Colicin B factors: superinfection immunity and represser susceptibility

F-like R factors are related to ColB-K77, but not to ColB-K98 or ColB-K166, by the criterion of superinfection immunity. Tests of de-repressed mutant R factors for susceptibility to repression by ColB-K98, known to produce represser for F, showed that these could be either repressor-sensitive or insensitive. The former were independently shown not to produce repressor, which was thus, presumably the reason for their de-repressed state.