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

Abstract

Studies on the enzymatic inhibition of phenylalanyl-tRNAPhe [from yeast] and formylmethionyl-tRNAFMet [from Escherichia coli] binding to the ribosomes [of E. coli] by defined tRNA fragments indicate that beside the anticodon the following regions of tRNA are important for ribosomal A-site interaction: the Tp.PSI.pCp sequence, the CpCpA end and hU loop. In contrast, binding to the ribosomal P site is not inhibited by uncharged yeast tRNAPhe fragments containing the hU or the T.PSI.C loop of the molecule. Comparative studies on the inhibitory effect of the oligonucleotides Tp.PSI.pCpGp and UpUpCpGp indicate that the presence of the minor bases in T.PSI.C loop is not an essential prerequisite for the binding of tRNA to the ribosomal A site. Furthermore, the binding of the Tp.PSI.pCpGp oligonucleotide to the ribosomes influences the ribosomal P site and increases the efficiency of the codon-anticodon interaction. The Tp.PSI.pCpGp probably binds to the ribomal A site and competes with the T.PSI.C 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 T.PSI.C loops of the tRNA and, therefore, suggests the dynamic involvement of tRNA in protein synthesis.