Stalled ribosome rescue factors exert different roles depending on types of antibiotics in Escherichia coli

Escherichia coli possesses three stalled-ribosome rescue factors, tmRNA·SmpB (primary factor), ArfA (alternative factor to tmRNA·SmpB), and ArfB. Here, we examined the susceptibility of rescue factor-deficient strains from E. coli SE15 to various ribosome-targeting antibiotics. Aminoglycosides specifically decreased the growth of the Δ ssrA (tmRNA gene) strain, in which the levels of reactive oxygen species were elevated. The decrease in growth of Δ ssrA could not be complemented by plasmid-borne expression of arfA , arfB , or ssrA AA to DD mutant gene possessing a proteolysis-resistant tag sequence. These results highlight the significance of tmRNA·SmpB-mediated proteolysis during growth under aminoglycoside stress. In contrast, tetracyclines or amphenicols decreased the growth of the Δ arfA strain despite the presence of tmRNA·SmpB. Quantitative RT-PCR revealed that tetracyclines and amphenicols, but not aminoglycosides, considerably induced mRNA expression of arfA . These findings indicate that tmRNA·SmpB, and ArfA exert differing functions during stalled-ribosome rescue depending on the type of ribosome-targeting antibiotic.