Contacts of elongation factor G with the small ribosomal subunit: Cross-linking approach

Translocation, the movement of mRNA-tRNA in the ribosome by one codon, is catalyzed by the elongation factor G (EF-G). Based on the ribosomal [1, 2] and EF-G [3] structures obtained, it is possible to study the molecular mechanism of translocation. The EF-G structure is similar to the structure of EF-Tu · aminoacyl-tRNA complex [4–6], which is responsible for the delivery of new aa-tRNA to the ribosome. The acceptor-stem of tRNA corresponds to the domain IV of EF-G. These data allow several hypotheses on the EFG role in translocation to be proposed. EF-G can directly interact with mRNA · tRNA complex in the Asite of the ribosome, thereby driving translocation, or the domain IV of EF-G may induce a change of the overall architecture of the ribosome, which, in turn, drives the rearrangement of the ribosome, leading to translocation [7, 8]. Chemical footprinting of EF-G on rRNA [5] shows that protections of several residues in the helix 34 of 16S rRNA depend on the EF-G binding to the ribosome. However, all these data do not allow us to suggest the existence of direct contacts between EF-G and the 30S ribosomal subunit.