CYTOCHROME-C BIOGENESIS IS INVOLVED IN THE TRANSPOSON TN5-MEDIATED BLEOMYCIN RESISTANCE AND THE ASSOCIATED FITNESS EFFECT IN ESCHERICHIA-COLI

The transposon Tn5 ble gene and the Escherichia coil alkylation-induci ble aidC locus are co-operatively involved in the resistance to the an ti-cancer drug and DNA-cleaving agent bleomycin and enhance fitness of bacteria in the absence of the drug. In this report, we demonstrate t hat the aidC locus is identical to nrfG, the last gene of the nrf oper on involved in the periplasmic formate-dependent nitrite reduction. In the presence of Sie, NrfG expression is specifically induced and rest ores both bleomycin resistance and its associated beneficial growth ef fect in an aidC(-) strain. In vitro DNA protection assays reveal that purified Sie prevents bleomycin-mediated DNA breakage, as do bleomycin -binding proteins. Similarities between haems of the cytochrome c biog enesis nrf pathway and iron bleomycin suggest a DNA repair-independent molecular mechanism for both bleomycin resistance and increased viabi lity. The Sie protein binds bleomycin and prevents DNA breakage. It al so induces the nrf locus that may assimilate bleomycin into haem for e xtracellular transport or inactivate bleomycin. Inactivation of potent DNA oxidants confers a better fitness to the bacterium carrying the t ransposon, suggesting a symbiotic relationship between host and transp oson.