Recognition of cognate transfer RNA by the 30S ribosomal subunit

Crystal structures of the 30S ribosomal subunit in complex with messenger R NA and cognate transfer RNA in the A site, both in the presence and absence of the antibiotic paromomycin, have been solved at between 3.1 and 3.3 ang stroms resolution. Cognate transfer RNA (tRNA) binding induces global domai n movements of the 30S subunit and changes in the conformation of the unive rsally conserved and essential bases A1492, A1493, and G530 of 16S RNA. The se bases interact intimately with the minor groove of the first two base pa irs between the codon and anticodon, thus sensing Watson-Crick base-pairing geometry and discriminating against near-cognate tRNA, The third, or "wobb le," position of the codon is free to accommodate certain noncanonical base pairs. By partially inducing these structural changes, paromomycin facilit ates binding of near-cognate tRNAs.