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Background  Accumulation of gyrase cleavage complex in  Escherichia coli  from the action of quinolone antibiotics induces an oxidative damage cell death pathway. The oxidative cell death pathway has also been shown to be involved in the lethality following accumulation of cleavage complex formed by bacterial topoisomerase I with mutations that result in defective DNA religation.    Methods  A high copy number plasmid clone spanning the  upp-purMN  region was isolated from screening of an  E. coli  genomic library and analyzed for conferring increased survival rates following accumulation of mutant topoisomerase I proteins as well as treatment with the gyrase inhibitor norfloxacin.    Results  Analysis of the intergenic region upstream of  purM  demonstrated a novel mechanism of resistance to the covalent protein-DNA cleavage complex through titration of the cellular transcription regulators FNR and PurR responsible for oxygen sensing and repression of purine nucleotide synthesis respectively. Addition of adenine to defined growth medium had similar protective effect for survival following accumulation of topoisomerase cleavage complex, suggesting that increase in purine level can protect against cell death.    Conclusions  Perturbation of the global regulator FNR and PurR functions as well as increase in purine nucleotide availability could affect the oxidative damage cell death pathway initiated by topoisomerase cleavage complex.

Resistance to topoisomerase cleavage complex induced lethality in Escherichia coli via titration of transcription regulators PurR and FNR