| Abstract: | Mutants of Escherichia coli K-12 re1A+-strain CP 78 resistant to fusidic acid (Fusr) were isolated and forms sensitive to high concentration of leucine (500 g/ml) were selected. When shifted down from nutrient broth to minimal medium M9 with supplemented glucose and required amino acids, these leucine-sensitive mutants continued RNA synthesis and demonstrated the prolonged lag-phase in contrast to the parent strain CP 78. Both properties are known to be characteristic of the Rel- strains. At the same time withdrawal of the required amino acids results in cessation of RNA synthesis in Fusr mutants, in the parent Rel+ strain. Thus, leucine-sensitive Fusr mutants show Rel- phenotype only upon amino acid starvation caused by shift down from nutrient broth to minimal medium. |
