Protection patterns of tRNAs do not change during ribosomal translocation

The translocation reaction of two tRNAs on the ribosome during elongation o f the nascent peptide chain is one of the most puzzling reactions of protei n biosynthesis. We show here that the ribosomal contact patterns of the two tRNAs at A and P sites, although strikingly different from each other, har dly change during the translocation reaction to the P and E sites, respecti vely, The results imply that the ribosomal micro-environment of the tRNAs r emains the same before and after translocation and thus suggest that a mova ble ribosomal do main exists that tightly binds two tRNAs and carries them together with the mRNA during the translocation reaction from the A-P regio n to the P-E region. These findings lead to a new explanation for the trans location reaction.