[How do ribosome binding sites recognize the functional state of tRNA?]

The order of relative affinity of three different functional form of tRNA (aminoacyl-tRNA, peptidyl-tRNA and deacylated tRNAOH) was established for three sites of the ribosome. The affinity increases for A-site in consecutive order: tRNAOH less than AcPhe-tRNA less than aa-tRNA; for P-site with messenger RNA: AcPhe-tRNA less than aa-tRNA less than tRNAOH; without messenger RNA: aa-tRNA less than AcPhe-tRNA less than tRNAOH; for E-site: (AcPhe-tRNA, aa-tRNA) much less than much less than tRNAOH. The dependence of association constants versus magnesium concentration for all forms of tRNA conforms the equation: delta lg Ka/delta lg[Mg2+] = n. Number "n" varies in the range 1 to 8 depending on the site of adsorption the form of tRNA and the presence of mRNA. Such magnesium dependence of affinity of tRNAs shows that the electrostatic interactions play an important role in the recognition of functional forms of tRNA by ribosomal sites.