Regions of tRNA important for binding to the ribosomal A and P sites.

Studies on the enzymatic inhibition of phenylalanyl-tRNAPhe and formylmethionyl-tRNAFMet binding to the ribosomes by defined tRNA fragments indicate that beside the anticodon the following regions of tRNA are important for ribosomal A-site interaction: the TppsipCp sequence, the CpCpA end, and hU loop. In contrast, binding to the ribosomal P site is not inhibited by the fragments of uncharged yeast tRNAPhe containing the hU or the TpsiC loop of the molecule. Comparative studies on the inhibitory effect of the oligonucleotides TppsipCpGp and UpUpCpGp indicate that the presence of the minor bases in TpsiC loop is not an essential prerequisite for the binding of tRNA to the ribosomal A site. Furthermore, evidence is presented that shows that the binding of the TppsipCpGp oligonucleotide to the ribosomes influences the ribosomal P site and increases there the efficiency of the codon-anticodon interaction. It is suggested that the TppsipCpGp binds to the ribosomal A site and competes there with the TpsiC loop of the aminoacyl-tRNA for the same binding site. A model for the interaction between tRNA and the ribosomal A site is proposed that involves partial unfolding of hU and TpsiC loops of the tRNA and, therefore, suggests the dynamic involvement of tRNA in protein synthesis.