The effects of Salmonella typhimurium on derepressed mutants of F-like factors

Abstract

SUMMARY: Derepressed mutants of F-like transfer factors, isolated by mutagenesis, were characterized as repressor-minus (i⁻) or operator-constitutive (o^c). Mutants of the i⁻ class are derepressed in K12 but repressed in Salmonella typhimurium. They are derepressed in S. typhimurium by a kanamycin resistance determinant carrying a locus der, described previously. Most o^c mutants of F-like factors are derepressed in both K 12 and S. typhimurium. However, one mutant of F-lac was o^c in K12 but was repressed in S. typhimurium. It was derepressed by der. Repression by S. typhimurium is different from that by fi⁺ factors, since der reverses the former but does not affect the latter. Possible interpretations of these findings are discussed.