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

Abstract

ABSTRACTTopoisomerase functions are required in all organisms for many vital cellular processes, including transcription elongation. The C terminus domains (CTD) ofEscherichia colitopoisomerase 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 coliwith atopA66single 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 thistopA66mutation. Consequently, the mutation frequency measured by rifampin selection following SOS induction was diminished in thetopA66mutant. The increased antibiotic sensitivity for thetopA66mutant can be reversed by the expression of recombinantE. colitopoisomerase I but not by the expression of recombinantMycobacterium tuberculosistopoisomerase I that has a nonhomologous CTD even though the recombinantM. tuberculosistopoisomerase I can restore most of the plasmid DNA linking number deficiency caused by thetopA66mutation. Direct interactions ofE. colitopoisomerase 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.