a, EVN allows for only brief accommodation of the acceptor end of aa-tRNA in the PTC (I and II). With the proper combination of the donor and acceptor substrates, peptide bond is formed during a short visit of aa-tRNA in the PTC active site and nascent peptide is transferred to the A-site tRNA (III). Translocation may possibly proceed without the antibiotic displacement (IV) or may require temporal ejection of the drug molecule (IIIa), followed by new rounds of translation. b, When the ribosome translates the EVN arrest motif, peptide bond formation is not fast enough to transfer peptidyl-residue to the A-site tRNA during its brief excursion into the PTC active site (V, VI). With the weak codon-anticodon interactions in the A-site the incoming aa-tRNA is rejected after few futile attempts (VII) resulting in pronounced ribosome stalling.