Mutants suppressing novobiocin hypersensitivity of a mukB null mutation

The mukB gene is essential for the partitioning of sister chromosomes in Escherichia coli. A mukB null mutant is hypersensitive to the DNA gyrase inhibitor novobiocin. In this work, we isolated mutants suppressing the novobiocin hypersensitivity of the mukB null mutation. All suppressor mutations are localized in or near the gyrB gene, and the four tested clones have an amino acid substitution in the DNA gyrase beta subunit. We found that in the mukB mutant, the process of sister chromosome segregation is strikingly hypersensitive to novobiocin; however, the effect of novobiocin on growth, which was measured by culture turbidity, is the same as that of the wild-type strain.