Ribosomal Protein S12 and Aminoglycoside Antibiotics Modulate A-site mRNA Cleavage and Transfer-Messenger RNA Activity in Escherichia coli*

Translational pausing in Escherichia coli can lead to mRNA cleavage within the ribosomal A-site. A-site mRNA cleavage is thought to facilitate transfer-messenger RNA (tmRNA)!SmpB-mediated recycling of stalled ribosome complexes. Here, we demonstrate that the aminoglycosides paromomycin and strep-tomycin inhibitA-site cleavage of stop codons during inefficient translation termination. Aminoglycosides also induced stop codon read-through, suggesting that these antibiotics alleviate ribosome pausing during termination. Streptomycin did not inhibit A-site cleavage in rpsL mutants, which express strepto-mycin-resistant variants of ribosomal protein S12. However, rpsL strains exhibited reducedA-sitemRNAcleavage compared with rpsL! cells. Additionally, tmRNA!SmpB-mediated SsrA peptide tagging was significantly reduced in several rpsL strains but could be fully restored in a subset of mutants when treate