Antimicrobial Susceptibility and SOS-Dependent Increase in Mutation Frequency Are Impacted by Escherichia coli Topoisomerase I C-Terminal Point Mutation

Topoisomerase functions are required in all organisms for many vital cellular processes, including transcription elongation. The C terminus domains (CTD) ofEscherichia coli topoisomerase I interact directly with RNA polymerase to remove transcription-driven negative supercoiling behind the RNA polymerase complex. This interaction prevents inhibition of transcription elongation from hypernegative supercoiling and R-loop accumulation. The physiological function of bacterial topoisomerase I in transcription is especially important for a rapid network response to an antibiotic challenge. In this study,Escherichia coli with atopA66 single nucleotide deletion mutation, which results in a frameshift in the TopA CTD, was shown to exhibit increased sensitivity to trimethoprim and quinolone antimicrobials. The topoisomerase I-RNA polymerase interaction and the SOS response to the antimicrobial agents were found to be significantly reduced by thistopA66 mutation. Consequently, the mutation frequency measured by rifampin selection following SOS induction was diminished in thetopA66 mutant. The increased antibiotic sensitivity for thetopA66 mutant can be reversed by the expression of recombinantE. coli topoisomerase I but not by the expression of recombinantMycobacterium tuberculosis topoisomerase I that has a nonhomologous CTD even though the recombinantM. tuberculosis topoisomerase I can restore most of the plasmid DNA linking number deficiency caused by thetopA66 mutation. Direct interactions ofE. coli topoisomerase I as part of transcription complexes are likely to be required for the rapid network response to an antibiotic challenge. Inhibitors of bacterial topoisomerase I functions and interactions may sensitize pathogens to antibiotic treatment and limit the mutagenic response.