Protection patterns of tRNAs do not change during ribosomal translocation.

The translocation reaction of two tRNAs on the ribosome during elongation of the nascent peptide chain is one of the most puzzling reactions of protein biosynthesis. We show here that the ribosomal contact patterns of the two tRNAs at A and P sites, although strikingly different from each other, hardly change during the translocation reaction to the P and E sites, respectively. The results imply that the ribosomal micro-environment of the tRNAs remains the same before and after translocation and thus suggest that a movable ribosomal domain exists that tightly binds two tRNAs and carries them together with the mRNA during the translocation reaction from the A-P region to the P-E region. These findings lead to a new explanation for the translocation reaction.