cysB and cysE mutants of Escherichia coli K12 show increased resistance to novobiocin

Summary Mutations in the cysB and cysE genes of Escherichia coli K12 cause an increase in resistance to the gyrase inhibitor novobiocin but not to coumermycin, acriflavine and rifampicin. This unusual relationship was also observed among spontaneous novobiocin resistant (Nov^r) mutants: 10% of Nov^r mutants isolated on rich (LA) plates with novobiocin could not grow on minimal plates, and among those approximately half were cysB or cysE mutants. Further analyses demonstrated that cysB and cysE negative alleles neither interfere with transport of novobiocin nor affect DNA supercoiling.