A CONFORMATIONAL SWITCH IN ESCHERICHIA-COLI 16S RIBOSOMAL-RNA DURING DECODING OF MESSENGER-RNA

Direct evidence is presented for a conformational switch in 16S riboso mal RNA (rRNA) that affects tRNA binding to the ribosome and decoding oi messenger RNA (mRNA). These data support the hypothesis that dynami c changes in rRNA structure occur during translation. The switch invol ves two alternating base-paired arrangements apparently facilitated by ribosomal proteins S5 and S12, and produces significant changes in th e rRNA structure, Chemical probing shows reciprocal enhancements or pr otections at sites in 16S rRNA that are at or very near sites that wer e previously crosslinked to mRNA. These data indicate that the switch affects codon-anticodon arrangement acid proper selection of tRNA at t he ribosomal A site, and that the switch is a fundamental mechanism in all ribosomes.