Mutual orientation of tRNAs and interactions between the codon-anticodon duplexes within the ribosome: a stereochemical analysis.

Analysis of the available data demonstrated that a codon in the i(th) codon-anticodon duplex should interact with the wobble pair of the i - 1(th) duplex. This interduplex interaction should take place throughout the ribosomal elongation cycle in order to prevent unprogrammed frameshifting. An experimentally observed flexibility of tRNA allows to conserve the interduplex interaction at different mutual orientations of tRNAs, including conventional R and S. Moreover, the tRNA flexibility allows novel mutual orientations of tRNAs in which tRNA molecules, as in conventional R and S orientations, also form the codon-anticodon duplexes, and the CCA-ends are located adjacently. The R and S orientations do not offer any advantages over the novel orientations. Therefore, besides the conventional R and S orientations, the novel orientations should also be considered, i.e. the interpretations of the available experimental data on the mutual orientations of tRNAs should be reconsidered. All mutual orientations of tRNAs that are compatible with the available experimental data are given.