Polyamines accelerate codon recognition by transfer RNAs on the ribosome.

The selection of aminoacyl-tRNAs by the ribosome is a fundamental step in the elongation cycle of protein synthesis. tRNA selection is a multistep process that ensures only correct aminoacyl-tRNAs are accepted while incorrect aminoacyl-tRNAs are rejected. A key step in tRNA selection is the formation of base pairs between the anticodon of the aminoacyl-tRNA and the mRNA codon in the A site, called "codon recognition". Here, we report the development of a new, fluorescence-based, kinetic assay for monitoring codon recognition by the ribosome. Using this assay, we show that codon recognition is a second-order binding step under optimal conditions. Additionally, we show that at low Mg(2+) concentrations, the polyamines spermine and spermidine stimulate codon recognition by the ribosome without a loss of fidelity. Polyamines may accelerate codon recognition by altering the structure and dynamics of the anticodon arm of the aminoacyl-tRNA.