Periodic conformational changes in rRNA: Monitoring the dynamics of translating ribosomes

In protein synthesis, a tRNA transits the ribosome via consecutive binding to the A (acceptor), P (peptidyl), and E (exit) site; these tRNA movements are catalyzed by elongation factor G (EF-G) and GTP. Site-specific Pb2+ cle avage was applied to trace tertiary alterations in tRNA and all rRNAs on pr e- and posttranslocational ribosomes. The cleavage pattern of deacylated tR NA and AcPhe-tRNA changed individually upon binding to the ribosome; howeve r, these different conformations were unaffected by translocation. On the o ther hand, translocation affects 23S rRNA structure. Significantly, the Pb2 + cleavage pattern near the peptidyl transferase center was different befor e and after translocation. This structural rearrangement emerged periodical ly during elongation, thus providing evidence for a dynamic and mobile role of 235 rRNA in translocation.